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■ SIMON SAYS Handheld Electronic Game Using Arduino

■ THE CLASSROOM The ATmega328P IC

■ PCBEASY How To Etch A PCB: Part 1

■ WHAT THE TECH Finger On The Pulse: Build Your Own Heartbeat Sensor

■ KEYLESS ENTRY RFID Access Control with Attendance Recording

■ WIRELESS SWITCHING Multi-zone WiFi Controlled Switch Using ESP8266

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Being part of the maker family generally means at some point or another you’ve encountered an ATmega328P. This humble microcontroller is cheap, robust, and easy to program, the backbone of many maker projects.

Generally speaking, the main reason we’ve heard of the ATmega328P is from using an Arduino, a development board centred around the Mega series of microcontrollers, specifically the Uno and Nano, which use different packages of the ATmega328P.

THE ATMEGA328P IC

The ATmega328P is the brains of many Maker projects. We take a look at this versatile chip, different ways to program it, and how to use one standalone.

DEAN CORVADIYODE Staff Writer


THE CLASSROOM


We’ve used the ATmega328P in its bare form in previous articles, however, let’s spend time just focusing on the ATmega328P, as you may learn something different from the Mega series in its wild form, outside its usual Arduino habitat.

But why use the ATmega328P on its own and not just stick to the development board? Simply put, we can significantly reduce the size of our projects. Once we’ve uploaded our code to the microcontroller, all the additional connections and components on the development board may not be necessary, such as the USB connector, or female pin headers. Thus, we can implement the microcontroller only with its necessary components to a breadboard or custom designed printed circuit board.

THE ATMEGA328P

Briefly summarising, the ATmega328P is an 8-bit microcontroller that operates on a RISC architecture. 8-bit means the processor uses an 8-bit register, which can handle 2^8 or 256 data values, which seems low for today’s standards, however, the higher the bit count and processing speed, the more power consumption the processor uses, hence, why microcontrollers are a favourable choice for low-power solutions.

The ATmega328P has many peripheral and special features that can be found in its 294-page datasheet(!). We can’t possibly list them all, otherwise, our article will become a datasheet also. Instead, we will focus on some key aspects that you may not have known about the ATmega328P.

1234567891011121314

2827262524232221201918171615

PC5 (ADC5/SCL/PCINT13)PC4 (ADC4/SDA/PCINT12)PC3 (ADC3/PCINT11)PC2 (ADC2/PCINT10)PC1 (ADC1/PCINT9)PC0 (ADC0/PCINT8)GNDAREFAVCCPB5 (SCK/PCINT5)PB4 (MISO/PCINT4)PB3 (MOSI/OC2A/PCINT3)PB2 (SS/OC1B/PCINT2)PB1 (OC1A/PCINT1)

(PCINT14/RESET) PC6(PCINT16/RXD) PD0(PCINT17/TXD) PD1(PCINT18/TXD) PD2

(PCINT19/OC2B/INT1) PD3(PCINT20/XCK/T0) PD4

VCCGND

(PCINT6/XTAL1/TOSC1) PB6(PCINT7/XTAL2/TOSC2) PB7

(PCINT21/OC0B/T1) PD5(PCINT22/OC0A/AIN0) PD6

(PCINT23/AIN1) PD7(PCINT0/CLKO/ICP1) PB0

ATm

ega3

28P

It is also the IC used on the Arduino Uno board. This PDIP package is really good for prototyping due to its breadboard compatibility. If the final solution of your project needs to be compact, the ATmega328P-MM is a 4 x 4mm surface-mount package to optimise your PCB space, however, these can be near impossible to solder by hand.

It is also the IC used on the Arduino Uno board. This PDIP package is really good for prototyping, due to its breadboard compatibility, but if the final solution of your project need to be compact, the ATmega328P-MM is a 4 x 4mm surface-mount package, optimising PCB space for other components.

APPLICATION AND PROGRAMMING METHODS

There are many methods to program your ATmega328P, and different ways to use an ATmega328P in a circuit depending on your application.

Over the following pages, we will describe four different projects that you can easily build and test for yourself.

We will explore four different programming methods so you can choose the best programmer for your projects. This includes using an Arduino Uno, an FTDI breakout board, and an In-Circuit Serial Programmer (ICSP).

We will also cover when to use the ATmega328P's internal oscillator or when you need to apply an external crystal oscillator.

LET'S GET HANDS-ON

To get started, you will need to get the parts that are common to all four builds, and the additional parts for the build you intend to make. ››

PARTS REQUIRED FOR ALL FOUR PROJECTS: JAYCAR ALTRONICS CORE ELECTRONICS1 x 16MHz Crystal (Not required for Build 4) RQ5296 V1289A COM-00536

2 x 22pF Capacitors* (Not required for Build 4) RC5316 R2814 CE05189

1 x LED* ZD0150 Z0800 CE05104

1 x 330Ω Resistor* RR2762 R0040 PRT-14490

* Quantity shown, may be sold in packs. You’ll also need a breadboard and prototyping hardware.

ZZ8727 ATMEGA328P MCU IC with Arduino Uno Bootloader MAGE CREDIT: jaycar.com.au


THE CLASSROOM


››For this example, we will transfer the ATmega328P IC on your Arduino Uno onto a breadboard to work stand-alone (We just use the Uno for power). First, let’s load the simple blink program onto the Uno.

With your Arduino Uno connected to your computer via USB, go to Tools › Board and ensure Arduino / Genuino Uno is selected.

Go to Tools › Port and select the port your Uno is plugged into, then select File › Examples › 01.Basics › Blink and upload to the Arduino Uno. We should now see the built-in LED on the Arduino Uno blinking every second.

Disconnect your Arduino Uno from USB so that it is powered off. Then, very carefully remove the ATmega328P from the Arduino Uno, and place it into a breadboard.

If you do not have access to an IC removal tool, an easy way to carefully remove the ATmega328P from the Arduino socket is by using a very thin flat-head screwdriver, and gently pry both ends back and forth until its removed, ensuring no pins are bent.

To operate this ATmega328P, we need a source of power. We also need

a 16MHz external crystal oscillator and two 22pF ceramic capacitors. Microcontrollers use an oscillation signal to generate a clock signal, which determines the speed the microcontroller operates its processes. This means the microcontroller conducts an operation every time there is a state change in the clock signal. Arduino uses an external crystal oscillator for this, meaning it operates at a processing speed of 16MHz. The ATmega328P actually contains its own internal oscillators, however, they are inferior to the external crystal in terms of stability. The capacitors used with the external crystal are there to resonate with the crystals inductance, meaning the crystal will resonate on its fundamental frequency.

To operate the blink program, we need an LED and 330Ω resistor, which will limit the current to the LED to avoid it burning out, and prevent too much current draw from the ATmega328P, as the maximum current draw per pin is 40mA.

Follow the schematic and Fritzing to wire your circuit. Use the Arduino as the source of power, as it contains a 5V regulated output. You will need to connect it to an available USB port on your computer or USB power source, or use a DC power supply. You should now see the LED blinking on your breadboard. Success!

Build 1:

Using an Arduino Uno Board

+5V

330D

19

7 20

PB1/PWMPB0AREF

PB2/PWMPB3/MOSI/PWM

PB4/MISOPB5/SCK

PC1/ADC1PC0/ADC0

PC2/ADC2PC3/ADC3

PC4/ADC4/SDAPC5/ADC5/SCL

PD0/RXPD1/TX

PD2/INT0PD3/INT1/PWM

PD4/XCK/TOPD5/PWMPD6/PWM

PD7

RESET/PC6

9XTAL1/PB610XTAL2/PB7

VCC

AVCC

22pF

22pF

8

GND

GND

GND

IC1ATmega328P

16MHz

16MHz

22

pF 2

p

ATmega328P

ADDITIONAL PARTS FOR BUILD 1: JAYCAR ALTRONICS CORE ELECTRONICS1 x Arduino Uno or Compatible XC4410 Z6280 A000066

1 x USB A-B Lead WC7906 P1911C FIT0056


THE CLASSROOM


In our first example, we used the Arduino to upload code to the ATmega328P. However, this isn’t the only option for using Arduino to upload code to the microcontroller.

This example uses an FTDI (Future Technology Devices International) board to communicate to the microcontroller via USB.

We can purchase the ATmega328P with Arduino bootloader pre-installed. A bootloader is a section of memory allocated in the microcontroller that runs prior to the main code, allowing the microcontroller to understand the main code, which in our case is the Arduino language. If you plan on using Arduino for the main code, this is an easy solution as we don’t have to upload the Arduino bootloader onto the ATmega328P ourselves.

Note: There are other bootloaders available also, such as optiboot, which is a simpler version that frees up 1.5k bytes of memory used in Arduino bootloader.

Following the schematic and Fritzing, connect the ATmega328P with bootloader and FTDI board.

We have selected an FTDI board that uses an Atmel ATmega8u2 with Arduino firmware loaded, meaning to an Arduino IDE, it appears as an Arduino Uno. Search for the board using the previous steps and upload the blink sketch to the ATmega328P.

It works! ››

Build 2:

Using an FTDI Board

+5V

19

7 20

PB1/PWMPB0AREF

PB2/PWMPB3/MOSI/PWM

PB4/MISOPB5/SCK

PC1/ADC1PC0/ADC0

PC2/ADC2PC3/ADC3


PD0/RXPD1/TX


PD4/XCK/TOPD5/PWM

DTRTXDRXIVCCNCGND

PD1

PD6/PWMPD7

RESET/PC6


VCC

AVCC

22pF

22pF

100nF

8

GND GND

+5V

GND

GND

IC1ATmega328P

16MHz

PD1

330D

5V

3.3V

DTR

TXD

RXI

VCC

GND

2p

F

16MHz

22

pF 2

p

ATmega328P

0.1

ADDITIONAL PARTS FOR BUILD 2: JAYCAR ALTRONICS CORE ELECTRONICS1 x ATmega328P with Arduino Bootloader^ ZZ8727 Z5126 DFR0081

1 x USB A to Micro B Lead WC7757 P1897A FIT0265

1 x 100nF Capacitor RG5125 R2736B CE05188

1 x FTDI board XC4594 Z6225 DFR0164

DFR0164 FTDI breakout boardIMAGE CREDIT: core-electronics.com.au

* Quantity shown, may be sold in packs. You’ll also need a breadboard and prototyping hardware. ^ The Jaycar ZZ8727 includes the 16MHz crystal.


THE CLASSROOM


››Now, let’s burn the Arduino bootloader to a fresh ATmega328P that currently has no bootloader on it. To do this, we will use what is called an In-Circuit Serial Programmer (ICSP).

Following the schematic and Fritzing, connect the ICSP to the breadboard. The ICSP tries to program at a clock speed of 375kHz, too fast for a brand new ATmega328P. Our ICSP has a jumper connector for “slow-clock”, which slows the programming speed to 8kHz.

Connect the “slow-clock” jumper, followed by connecting the USB of the ICSP to the computer.

Windows users will need to install a driver for the ICSP located on the manufacturer’s website. Mac and Linux users do not need to install drivers.

On the Arduino IDE, locate Tools › Programmer › USBasp.

To upload the Arduino bootloader, select Tools › Burn Bootloader. Once the bootloader has been installed, we can upload the blink sketch to the microcontroller by selecting Sketch › Upload Using Programmer. Once again you should have a blinking LED!

Build 3:

Using an In-Circuit Serial Programmer (ICSP)

+5V

191817

7 20

PB1/PWMPB0AREF

PB2/PWMPB3/MOSI/PWM

PB4/MISOPB5/SCK

PC1/ADC1PC0/ADC0

PC2/ADC2PC3/ADC3


PD0/RXPD1/TX


PD4/XCK/TOPD5/PWM

GNDMOSIVOUTRSTSCKMISO

PD6/PWMPD7

RESET/PC6


VCC

AVCC

22pF

22pF

8

GND GND

+5V GND

GND

IC1ATmega328P

16MHz

SCK

SCK

330D

1

MOSIMISO

MOSI

MISO 5V3.3V

VOUTMISO

SCK

RST GND

MOSI

USBASP

2p

F16MHz

22

pF 2

p

ATmega328P

ADDITIONAL PARTS FOR BUILD 3: JAYCAR ALTRONICS CORE ELECTRONICS1 x ATmega328P^ ZZ8727 Z5125 002-556-ATMEGA328P-PU


1 x USBasp ICSP XC4627 Z6540 CE04564* Quantity shown, may be sold in packs. You’ll also need a breadboard and prototyping hardware. ^ The Jaycar ZZ8727 includes the 16MHz crystal.

CE04564 USBasp ICSP Programmer.IMAGE CREDIT: core-electronics.com.au


THE CLASSROOM


Let’s move away from Arduino now and use the ATmega328P in its bare form, and program using compilers other than Arduino, such as C++ and C.

The manufacturer of the ATmega328P, Atmel, offer programming of the microcontroller using their software, Atmel Studio. This software is free to download, with the latest revision being Atmel Studio 7, however, it only operates on Windows and is a large program, intended for the professional market.

Using this software, we can use the full potential of the ATmega328P. This includes operating a clock speed from as low as 1MHz up to a maximum of 20MHz and an operating voltage from as low as 1.8 volts up to 5.5 volts. We can select the internal crystal using Atmel Studio, AVRfuses, and other options. ››

Build 4:

ATmega328P Programmed Using C

+3.3V

191817

7 20

PB1/PWMPB0AREF

PB2/PWMPB3/MOSI/PWM

PB4/MISOPB5/SCK

PC1/ADC1PC0/ADC0

PC2/ADC2PC3/ADC3


PD0/RXPD1/TX


PD4/XCK/TOPD5/PWM

GNDMOSIVOUTRSTSCKMISO

PD6/PWMPD7

RESET/PC6

XTAL1/PB6XTAL2/PB7

VCC

AVCC

8

GND GND

IC1ATmega328P

SCK

SCK

MOSIMISO

MOSI

MISO

330Ω

+3.3V

VOUTMISO

SCKRST GND

MOSI

ATmega328P

3.3V

ADDITIONAL PARTS FOR BUILD 4: JAYCAR ALTRONICS CORE ELECTRONICS1 x ATmega328P ZZ8727 Z5125 002-556-ATMEGA328P-PU


1 x ICSP (eg. Atmel-ICE or similar. See text.) Element 14: 2407172

* Quantity shown, may be sold in packs. You’ll also need a breadboard and prototyping hardware. ^ The Jaycar ZZ8727 includes the 16MHz crystal.

2407172 ATMEL-ICE Basic Debugger. IMAGE CREDIT: element14.com


THE CLASSROOM


››Programming using Atmel Studio involves an ICSP programmer. We used the Atmel-ICE programmer as this is supported in Atmel Studio and by AVRdude, however, the USBasp is compatible with Atmel Studio 7 (It’s just a very tedious process that could be an article in itself).

Follow the schematic and Fritzing, and connect the ICSP programmer you intend you use.

Download the Atmel Studio hex code from the DIYODE website, and upload it to the ATmega328P by selecting Build › Build Solution, followed by Tools › Device Programming › Tool (ICSP Programmer) › Device (ATmega328P) › Interface (ISP).

Then, read the Device Signature, followed by Memories › Flash › Program.

You should once again see a blinking LED!

This code operates off a 1MHz clock signal and can operate from a 3.3V source. But why? Well as mentioned earlier, operating off a slower clock signal and operating voltage can reduce the power consumption of the device.

Operating a green 10mm LED off an ATmega328P running at 16MHz, powered by 5 volts with Arduino bootloader, resulted in a measured 16mA during active state and 22mA when LED illuminated.

Using the same LED off an ATmega328P running at 1MHz on 3.3 volts using Atmel Studio C code resulted in a measured 1.3mA during active state and 3mA when the LED illuminated. That’s 110mW compared to 10mW, a 100mW power saving! All the while doing the exact same functionality.

We can also operate with a faster clock speed of 20MHz. This is helpful with faster data transfer speeds between communication protocols. Although we sacrifice a higher power consumption, we can transfer the data faster, meaning a higher power consumption is achieved for a shorter duration. Better than a lower power consumption for a longer duration, as processing is slower and could result in the same overall power consumption.

IN SUMMARY

If low power consumption is the highest priority for your application, then the last method would be your best solution. If you are prototyping a quick solution with minimal code and multiple microcontrollers then the third solution would be the best solution, as ICSP can program multiple devices at once and Arduino bootloader is easy to program. ■

WANT MORE?For the code, or to discuss this edition of The Classroom, visit: https://diyode.io/036scgs


THE CLASSROOM


KEYLESS ENTRY RFID Access Control with Attendance Recording


PROJECT

Grant access to multiple users to a room or system using RFID technology, and record the date and time on when they enter.

JOHANN WYSSDIYODE Staff Technical Writer


BUILD TIME: 3 HOURS (+ 3D PRINTING TIME) DIFFICULTY RATING: INTERMEDIATE

We see RFID (Radio Frequency Identification) technology used in many parts of our life these days, from ticketing systems on public transport to gaining entry to our workplaces. Gymnasiums, for example, use the technology to grant access to members at any time of day or night, and record the member’s attendance without any staff at the gym at the time. RFID tags are in our passports, the DVDs we rent from the local kiosk, in the books we borrow from the library, and much more. Consider also the tag stuck to your car’s windscreen that beeps when you pass under a toll point.

Using RFID technology for gaining access to a room or building means there’s no need for physical keys that can be lost, stolen and copied, which could mean replacing your locks in some circumstances. It also means you know specifically who is entering based on their unique RFID number, and with the right systems in place, you can record the date and time of them entering.

This brings us to our project, which makers can build using commonly available RFID tags and readers.

THE BROAD OVERVIEW

For this project, we are building an RFID ingress control system that will give you the ability to control an electronic door lock and record the time and details of the person who used it.

The project uses an RFID reader module, various RFID tags, key-fobs and wafer cards, an RTC (Real Time Clock) module for timing purposes, and an SD Card Module to store the data. All managed by an Arduino Uno microcontroller, with information displayed on an LCD screen.

In our application, we will trigger an electronic door lock, however, you could just use the system for attendance purposes or to trigger other devices.

HOW IT WORKS

RFID TECHNOLOGY

RFID technology is an exciting field that was developed in the 1980s as a replacement for the humble barcode. The benefits of the technology are that you don’t need a line-of-sight to read the information as a barcode does. This means your products zipping down a production line don’t all need to be sorted in a way that the barcode is in a position ready to be scanned. This technology became a revolution in the manufacturing industry and is now widely being used across many industries.

Other RFID applications include:

• Small RFID chip implanted in pets to help identify the owner if it escapes.

• Passport and driver's license to provide rapid data verification as well as making it very difficult to make fraudulent copies.

• Retail stores use the technology as a means of detecting and preventing theft of their merchandise.

• Video game add-ons, such as Skylanders™ to identify which character you’re playing with.

Whilst we use RFID in our everyday lives, for the most part, most of us know very little about how it works.

There are two types of RFID tags:

• Passive, powered via the RFID reader.

• Active, with the RFID chip powered by a small battery.

Both technologies are essentially the same, however, the active with its battery gives the chip significantly more range. Passive RFID cards, like the ones we are using for this project, have a maximum transit / receive distance of about 10 metres, whereas the RFID chip in your car’s toll reader has a maximum read distance of up to 100 metres.

With that said, the maximum transmit distance relies on various factors including the transmit power. For this project, we found that the combination of this reader and the supplied RFID cards the maximum transmit / receive distance was about 50mm.

To get into how the RFID system works, we need to take a look at the tags themselves. To do this, we decided to open up one of the supplied RFID tags.

The electronics inside are little more than a coil of wire, and a small IC hidden under a blob of epoxy. ››


PROJECT


››When a tag is brought close to the reader, the reader's coil is inductively coupled to the coil on the RFID tag. This coupling allows a small amount of energy to be wirelessly transferred from the powered reader into the coil of the RFID chip to power the small IC. Naturally, for inductive coupling to work, the RFID reader must transmit a constantly changing / pulsating DC i.e. an AC signal called the carrier wave. For the RFID module and cards, we are using this carrier wave that has a frequency of 13.56MHz, that’s 13.5 million cycles per second!

As you can see in the image shown here, there is a coil around the perimeter of the lower section of the RFID reader’s circuit board. This coil allows a small amount of energy to transfer from the reader into the RFID card to power it.

Interestingly, the RFID chip on the card does not actually transmit anything in the traditional sense. Instead, the data is transferred via a process called load modulation or task manipulation. The IC on the RFID card turns a load attached to the coil on and off in sequence to the data stored on the card.

This switching of the load causes the coil on the RFID card to consume more current. This causes the voltage on the RFID reader’s coil to sag when the load on the card is active. By reading the voltage at the antenna / coil of the RFID reader, we can detect the highs and lows, and therefore, create a data stream of ones and zeroes.

This data stream is then decrypted if needed, and can be processed as normal. The cards we are using have a maximum data storage of 1Kb, which means quite a significant amount of data can be stored on the card itself. However, for this project, we are simply going to use the unique identifier (UID) for each card to differentiate it from other cards.

Note: It is possible to change the UID on a card, so using the RFID UID is not a secure method. Therefore, you should avoid using such technology as the only means of protecting anything valuable.

1...

0...

1... 1...

0...Data

13.56MHz Load Modulation BehaviourReceiver

Reader FX

Carrier13.56MHz

Reader

We will write a program that reads the RFID UID of a card. If the UID matches the UIDs stored in the program, it will display a welcome message on an LCD and record the action onto an SD card. After this, it pulls a digital pin high, which can be used as a signal to control a device such as a solenoid or electronic door strike, such as this one from Jaycar.

RIGHT ►LA5077 Door Strike from Jaycar.

Keep in mind that the signal from our project isn’t adequate to trigger a solenoid or door strike directly, so we need to use a relay or other means to control such large loads. There are many ways to do this, ranging from transistors to relays, with arguably the most convenient being a relay.

When using a relay module, the signal wire is galvanically isolated from the connecting circuitry by the use of an integrated optocoupler. A transistor is also used to allow sufficient current through a relay coil to actuate it. When pulled high, the signal wire allows current to flow into the optocoupler input, which allows current to flow from VCC and through the output of the optocoupler. This current then flows into a transistor which allows current to flow from VCC through the coil of the relay and through the transistor to ground. The current flowing through the relay coil causes it to magnetise the relay wiper, pulling the wiper of the relay from the Normally Closed (NC) position to the Normally Open (NO) position. This allows current to flow from the Common (COM) pin into the normally open (NO) pin.

How you connect the hardware to this will depend on your specific system, however, most door locks will require a high pulse to activate them as they want the door to remain locked in the event of a power outage. As such, they should be connected to the normally open connection of the relay.

R11K

U1

817C

123

R2 510Ω Q1

D1 5

K1

4

RY-VCC

J1GND

3 2 1

VCC Signal

NC

NOCOM

No Voltage

NC

NOCOM

Voltage Applied5V


PROJECT


The Prototype:ELECTRONICS

Use the Fritzing diagram and connection guides shown here to wire up your prototype circuit.

Note: You will notice that the modules share the same pins on the Arduino Uno. For the prototype, you can overcome this by using a breadboard.

REALTIME CLOCK

The Realtime Clock uses the I2C protocol, and as such, shares the same pins as the LCD backpack. ››

REALTIME CLOCK ARDUINO UNOGND GNDVCC 5VSDA Analog 4SCL Analog 5DS N/C

PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 x Arduino Uno or Compatible XC4410 Z6240 CE05629

1 x RFID Module with RFID Card or Tag XC4506 Z6356 CE07140

1 x SD Card Module XC4386 Z6353 CE05113

1 x Realtime Clock Module XC4450 - CE07141

1 x 1602 LCD Screen QP5521 Z7002A DRF0063

1 x I2C Backpack for LCDs XC3706 - 018-LCD1602-I2c

1 x Relay Module XC4419 Z6325 CE05137

1 x SD Card (Formatted to FAT16 or FAT32) XC4989 D0328 CE04628

You’ll also need a breadboard and prototyping hardware.


PROJECT



PROJECT


››SD CARD MODULE

The SD card module uses the SPI communication protocol.

RC522 RFID MODULE

Like the SD card module, the RFID module also uses the SPI communication protocol.

Note: The RFID module’s VCC requires 3.3V. Powering it to 5V will damage the module. The data pins, however, can support 5V.

LCD SCREEN

The LCD utilises the I2C backpack, which must first be soldered onto the back of the 1602 LCD (see notes below). This backpack reduces the number of pins for the LCD from 16 down to 4.

LCD BACKPACK

The I2C LCD backpack needs to be soldered to the 1602 LCD. For this project, we opted to solder the backpack directly to the LCD using the supplied male header. Ideally, you would join these

SD CARD MODULE ARDUINO UNOGND GND

+3.3V 3.3V+5V N/C

CS (Chip Select) Digital Pin 8MOSI (Master Out Slave In) Digital Pin 11

SCK (Serial Clock) Digital Pin 13MISO (Master In Slave Out) Digital Pin 12

GND GND

RFID MODULE ARDUINO UNOVCC 5VRST Digital Pin 9GND GND

MISO (Master In Slave Out) Digital Pin 12MOSI (Master Out Slave In) Digital Pin 11

SCK (Serial Clock) Digital Pin 13NSS (Active Low Slave Select) Digital Pin 10

IRQ (Interrupt) N/C

LCD BACKPACK ARDUINO UNOGND GNDVCC 5VSDA Analog 4SCL Analog 5

together by using a female header on the LCD so that the two modules can be separated. In our application, however, this would mean the faceplate would have to be 9mm thicker, which we figured would make the project way too bulky.

It is important to note, if you do solder the backpack directly to the module, the backpack may foul against the LCD’s metal frame and potentially cause a short circuit.

To overcome this, we used a piece of cardboard to act as a spacer between the Backpack and the LCD module, ensuring that when we solder the backpack into position that there is sufficient clearance. This cardboard can be removed after soldering if desired.

Before we move on, it’s important to double-check the address of your I2C LCD backpack. To do this, we use the I2C scanner program that you can find on the Arduino playground here: https://playground.arduino.cc/Main/I2cScanner/

With the I2C LCD connected to the Arduino, run this sketch and it will display the address of your LCD on the serial monitor. You will need to record this address as it will need to be added to this line of the main program.

You simply replace the text ‘address here’ with the hex value provided by the I2C scanner sketch. In most cases, the I2C backpack will have the address 0x26, and as such, we have left the main code as this. ››

LiquidCrystal_I2C lcd =

LiquidCrystal_I2C(address here, 16, 2);

LiquidCrystal_I2C lcd =

LiquidCrystal_I2C(0x26, 16, 2);


PROJECT

https://playground.arduino.cc/Main/I2cScanner/


››None the less, it’s easier to identify the address now than troubleshooting later with the circuit constructed. It will save you lots of time if the address is different on your module.

THE CODE

INSTALLING THE LIBRARIES

This sketch uses several libraries generously provided by various members of the Arduino community for us to use. In order for the code to successfully compile and upload to the Arduino Uno, you will need to install them. To do so, simply search for and install them directly from the Arduino Integrated Development Environment (IDE).

Select Tools > Manage Libraries or press Ctrl+Shift+I.

Use the filter in the search section to find the necessary libraries, and select Install for each one.

The SPI.h library is now part of the standard Arduino lineup and won’t need to be manually installed. If you get an error related to this library, we recommend you upgrade to a newer version of the Arduino IDE.

THE CODE

The code is too long to include in its entirety in the magazine. It is available to download from our website, and we will simply explain the main functions here. We have attempted to make the code as portable as possible to enable makers to easily modify certain parameters to suit their application.

Our code uses five different RFID cards, along with five arbitrary names. Naturally, these values will need to be changed to suit your application. The first value you will need to change is the value stored in the constant called CARDS.

#define CARDS 5

This defines how many cards you will be using, change the 5 to the number you will have installed.

The string named 'building' allows you to name the building that this RFID device is controlling ingress too.

This string can be a maximum of 16 characters so that it fits on the 16-character display. To centre the name on the screen you can change the value stored in:

To do this, you simply do a little math: (16 − characters in building name) / 2.

If the building name has 6 characters like DIYODE does its ((16 – 6)/2) which is 5.

This should be a whole number so if you get a fraction you will need to simply round up or down. However, the code will do this for you.

You can now store the unique card IDs for each of the cards you intend to use in the following two-dimensional array.

byte UID[CARDS][4] = {

Note: When storing the unique IDs, you can ignore the leading zeros of a number.

String building = (“DIYODE”);

#define pos 5

{171, 38, 239, 26},

{105, 54, 171, 213},

{194, 96, 17, 28},

{78, 67, 68, 209},

{138, 14, 113, 151}

};


PROJECT


If you don’t know what the UID is for a card you can use the READNUID example from the RFID / MFRC522 library. This example will scan an RFID card and display the unique ID via the serial monitor.

This will allow you to discover and record the UID of each card you intend to use. Simply add the decimal value to the array. You will need to keep track of the RFID cards, so you may want to consider writing on or otherwise marking the card in a way so that you know its position in the array. This will make it much easier when assigning a name to that position.

With the UID identified and recorded for each of the cards you intend to use you can now assign them to a person, and thus record the names in the program by changing the names array.

In order to fit the name on the LCD screen, the names must be 16 characters or less. The position of the name directly correlates with the position of the UID. Therefore, the first element of the names array is matched with the first 4 elements of the UID array.

POSITION UID NAME

0 171 38 239 26 Jane White

1 105 54 171 213 Jack Black

2 194 96 17 28 Peter Grey

3 78 67 68 209 Sally Green

4 38 14 113 151 Max Power

These are the only values that you are likely to need to change to customise the project for your specific needs.

String names[(CARDS)] = {

“Barry White”,

“Jack Black”,

“Peter Gray”,

“Sally Green”,

“Max Power”

};

All in all, the code itself is fairly straightforward and written completely in functions. The first function readCard() was derived from the READNUID example code provided with the MFRC522 library. We modified this example to make it more useful for our desired project.

This function reads the UID and stores each 3-digit number into an array of 4 elements while omitting the leading zeroes.

From there, we enter the compare function to compare the elements in each array, looking for a match. If a match is found, we enter the displayUID() function and display a welcome message on the LCD. We also initiate a timer used to later clear the display back to the default.

After the displayUID function, we enter the write data function which writes the date, time, unique card number and personnel name to the SD card.

The code then enters the unlock function which pulls a digital pin high for the duration of a timer. This duration is by default set to 2000mS and can be adjusted if needed by changing the variable delayTime.

This means the door will remain unlocked and welcome message will be displayed for 2 seconds after a known card is detected. After this time, the digital pin is pulled low and the LCD returns to the default setting.

The SD card records the date and time of the unlock as well as the unique ID and name of the person who owns the card.

Likewise, the data is also sent serially for situations where the device is attached to a computer for real-time monitoring. The output will look similar to this screenshot. ››


PROJECT


NO MORE

LEMONSSUBSCRIBE TODAY: diyodemag.com/036subs

http://diyodemag.com/036subs

The Main Build:››To turn our prototype into something more permanent, we designed two 3D printed enclosures so we could mount the LCD and RFID reader in one location and the SD card, Realtime clock and Arduino in another area. This way, the LCD and reader can be on one side of a wall and the sensitive electronics can be on the other side, protected in an enclosure. ››

ADDITIONAL PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 × Pack of 100mm Cable Ties HP1196 H4031A FIT0343

1 × Female Pin Header Strip HM3230 P5390 PRT-00115

1 × Male Pin Header Strip HM3211 P5430 POLOLU-965

Heatshrink Tubing WH5520 W0882 ADA1649


PROJECT


LCD-I2C-CONVERTER

RTC-EEPROM-BATTERY

CARD-SD-ADAPTER

D0D1D2*D3D4*D5*D6D7D8*D9

*D10*D11D12D13

A0A1A2A3A4A5VINRESET

5VAREFGN

DGN

DGN

D

3.3V

IOREF

SDASCL

VCCM

ISOM

OSISCKRESETGN

D

GND

J1.4

SCLJ1.3

SDAJ1.2

VCCJ1.1

VSS J2.1VDD J2.2VEE J2.3RS J2.4R/W J2.5

DB0 J2.7DB1 J2.8DB2 J2.9DB3 J2.10DB4 J2.11DB5 J2.12DB6 J2.13DB7 J2.14LED.A J2.15LED.K J2.16

EN J2.6

GND.1

J1.1VCC.1

J1.2SDA.1

J1.3SCL.1

J1.4DS.1

J1.5

BATJ2.1

GND.2

J2.2VCC.2

J2.3SDA.2

J2.4SCL.2

J2.5DS.2

J2.6SQ

J2.7

GND.1

1

3V33

5V5

CS7

MOSI

9

SCK11

MISO

13

GND.2

15

12345678

RFID MODULE

ARDUINO UN

O R3

VCC.1J1.3

IN1

J1.2

GND

J1.1

VCC.2J2.2

JD-VCCJ2.1

RELAY-1-SRD

3.3VRSTGNDMISOMOSISCLKNSSIRQ

SD CARD

K1

Connect the relay to yoursolenoid/door control hardware


PROJECT


››3D PRINTED ENCLOSURE

We have designed custom 3D printed enclosures to suit the modules. The print files can be downloaded from our website.

Note: If you don’t have access to a 3D printer, you could use Jiffy boxes or similar enclosures from your favourite electronics or hardware store, and use the appropriate mounting hardware. An electrical junction box could be fastened (screwed) to the back of a rectangle of brushed aluminium or stainless steel sheet for an extra "security" message. Add a dummy lens for an extra strong message.

INPUT PANEL

The input panel houses the LCD display and the RFID module, and needs to be mounted to the external wall of your secure room or building.

Note: This 3D printed enclosure is in no way weather resistant so it is only suitable for internal mounting.

This input panel allows the user to touch their card or keyfob to the faceplate and receive a welcome message if their login is successful.

The faceplate was printed on our Flashforge Creator Pro at a 200-micron layer height using black 3D Fillies brand PLA. It’s designed to print without supports and laying flat on the build surface as shown. It takes about 3.5-hours to print.

The faceplate has four mounting holes that will allow you to screw it directly to the wall adjacent to the door entry. The cables will need to be routed through the wall so they can be connected to the control box.

CONTROL BOX

The second enclosure will house the RTC, Arduino Uno and the SD card, and is mounted on the other side of the wall so that it cannot be easily reached by unauthorised individuals. We made two holes in the case to allow the user to attach and power the device from the USB port. This will also allow for real-time serial output. There is also a slot that allows the user to insert and remove an SD card.

There is also the option to power the Arduino directly via the Vin pin if desired which will allow the user to power the device from a 6–20V supply. This is handy as 12V is a very common voltage for door locks and solenoids. This means you can power the device from one single power supply, and even add a 12V UPS in case the power goes out.

Like the faceplate, the control box and lid were both printed on our Flashforge Creator Pro at a 200-micron layer height using Flashforge branded black PLA. The control box took 4-hours to print, and is printed without supports in the orientation shown.

Note: Depending on your slicer and printer’s capabilities, you may find you need support material to bridge the overhangs for the SD card slot and the Arduino’s USB port. Take this into consideration when slicing the files.

The lid took about 1.5 hours on the Flashforge and press fits into the control box. You may find that you get little blobs of stitching on the rim of the lid where it fits into the control box. This stitching ››


PROJECT


››is a seam where the 3D printer transitions from one layer to the next. If your slicer does this in the same position on every layer you get a very noticeable seam running vertically along the print. This seam may cause the lid to not fit correctly. If this is an issue for you, you can use a hobby knife to carefully remove the little extra plastic.

To help reduce the amount of work required to remove this seam, make sure your slicer is not set to starting and stopping each layer at a random spot.

Note: Some small issues were discovered during the assembly and the design has been modified to rectify these issues, thus you may notice some slight differences between the images here and the files you will be printing.

PROJECT ASSEMBLY

To assemble the project, we need to create a simple wiring harness that will connect each component to the Arduino Uno. This was quite possibly the most time-consuming part of the project. You need to make the cables as short as practical to reduce wastage and filling the control box with coils of wire. The best way we found to do this was to first attach the modules to the enclosure in their positions.

Screw the Arduino down with just one screw as you will need to remove the Uno later to run the cables through the hole in the back of the enclosure. This hole is designed to line up with a hole in the wall it’s mounted to, which will allow the cables to link both units.

Starting with the control box, secure the RTC module, SD card module, and Arduino Uno using #4 screws.

We then cut a male pin header strip that we had available.

One 2-pin strip to attach SCL and SDA of the LCD and RTC to analog pins A5 and A4 of the Arduino Uno.

One 4-pin strip to go into the two ground pins, 5V pin, and 3.3V pin of the Arduino Uno. This will provide the power and ground signals for the modules.

One 6-pin strip for digital pins 8 – 13 of the Arduino Uno. These pins are the SPI signal wires for the RFID module and the SD card module.

Likewise, we created a similar plug for each of the modules using female headers.

A 4-pin female header strip was made for the I2C LCD.


PROJECT


An 8-pin female header strip was made for the SPI SD card module (only 6 wires were connected).

A 4-pin female header strip was made for the I2C RTC module.

An 8-pin female header strip was made for the SPI RFID module (Only 7 pins were used).

To join the wires, we first stripped about 10mm of the insulation away, giving us plenty of room to work. We then placed two wires parallel to each other and twisted the exposed wires together to form a strong mechanical bond. We then slid a 20mm length of heatshrink over these two wires (to insulate the join after soldering). We then twisted the third wire around these two and soldered all three wires together.

Once soldered you can insulate the join by sliding the heatshrink over the solder connection and apply heat to shrink it. You can also use electrical tape or liquid electrical tape if you wish. This technique will produce a very strong join for three wires, and will need to be used on most connections in this project. Take your time and you will get great results.

Once you’re done, you can simply use the male and female pin headers as a plug and socket to join all of the modules to the Arduino Uno.

Note: The wires for the RFID module and LCD need to be routed underneath the Arduino Uno and through a hole on the bottom of the controller enclosure.

When everything is placed and working correctly you should use cable/zip ties to keep the wires in check and to prevent twisting, knots or strain on connections.

PROGRAMMING

If you’re new to Arduino or having issues getting started you may want to check out our "Setting up the Arduino IDE guide" from Issue 17 where we go through the fundamentals of using the Arduino from the install process to adding libraries and uploading a sketch on various different operating systems. You can find it here: https://diyodemag.com/education/fundamentals_setting_up_the_arduino_ide ››


PROJECT

https://diyodemag.com/education/fundamentals_setting_up_the_arduino_ide

https://diyodemag.com/education/fundamentals_setting_up_the_arduino_ide


››TESTING & TROUBLESHOOTING

Testing the prototype is fairly straightforward for this project. We have added some basic error messages to help identify potential faults. Below are the potential errors and how to rectify them.

BLANK LCD

If there is no information displayed on the LCD, your first action should be to adjust the potentiometer on the back of the I2C backpack module. This potentiometer adjusts the contrast of the display and should make the display visible.

If this does not rectify the display issues, double-check the connections. Make sure the SDA, SCL and power and ground connections are correct. If the fault is still not rectified, ensure that the code has been correctly uploaded to the microcontroller.

You should also double-check that the address set in the code matches the address of the LCD. You can use the Arduino playground I2C scanner to do this, as mentioned earlier.

RTC FAILURE

This error message will be displayed on the LCD if there is an issue with communication between the microcontroller/Arduino and the RTC module. This would normally occur if the SCL and SDA connections are incorrectly connected, or insufficient power is being delivered to the module.

Double-check all connections and rectify any potential issues. If this error persists, consider switching the module to ensure it is functioning correctly.

NO SD CARD

If you see ‘No SD Card’ displayed on the LCD, the most likely cause is that the SD card has not been inserted or is the wrong format. Make sure that the SD card is correctly inserted and that the formatting is in the FAT16 or FAT32 (file allocation table) format. Most SD cards come supplied from the factory in this format, however, if the SD card has been used in other devices such as a camera or media player etc., you may need to reformat it.

If that still does not rectify the fault double-check that the wiring is correct and that the modules are receiving the correct voltage.

WHERE TO FROM HERE?

As a door access and logging device there isn’t too far to push this project. Naturally, making it wireless and recording the data to an online cloud would be the most obvious improvement. However, the technology used is both pretty impressive and prevalent. Using just the objects on hand, we were able to retrieve data from a Queensland driver's license, a United Kingdom passport, public transport cards, Visa payWave cards and various student IDs. In fact, its highly likely that this reader will work with any RFID chips designed to run on the 13.56MHz frequency. Of course, the data is always going to be encrypted, and thus it is only for an educational benefit. ■

WANT MORE?For the code and 3D print files, or to discuss this project, visit:https://diyode.io/036xpyy


PROJECT

https://diyode.io/036xpyy


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WIRELESS SWITCHING

Multi-zone WiFi Controlled Switch

using ESP8266

FRASER BORDEREngineer | Educator | Founder of IntegratedSTEM

& DIYODE Staff Writer

integratedstem.com.au

BASEM ADELLead Engineer at IntegratedSTEM

& DIYODE Staff Writer

integratedstem.com.au

Control multiple systems distributed across your WiFi network at the

touch of just one button.

BUILD TIME: 30 MINUTES (+ 3D PRINTING TIME) DIFFICULTY RATING: INTERMEDIATE

Issue 036 July 2020diyodemag.com 35

PROJECT

http://integratedstem.com.au

http://integratedstem.com.au


››The original intention for this project was to distribute “ON AIR” signs around our office that would illuminate when the team were filming in the studio. The solution needed to be simple, take advantage of the WiFi network to reduce wiring, and expandable so that additional signs could be added around the office.

THE BROAD OVERVIEW

Thanks to Arduino-compatible modules becoming popular, wireless communication has become a viable, affordable option to be used in relatively simple projects like this. Many of these utilise Bluetooth or WiFi communication protocols, removing the constraints of wired network connections, which is why we have chosen to use the ESP8266 for this application.

The diagram shown here exemplifies the WiFi communication between devices using this popular ESP8266 microcontroller.

We will take advantage of this compact microcontroller and its WiFi communication for our project.

Internet

Access Point

Station (ESP8266)

RST

A0

D0

D5

D6

D7

D8

3V3

TX

RX

D1

D2

D3

D4

GND

5V

RESET D1 mini

HOW IT WORKS

The project has been divided into two circuits, the server circuit and client circuit. The client circuit has a pushbutton, and upon being pressed, the LED connected to the client circuit will be turned on. A signal will then be sent from the client circuit to the server circuit via the local WiFi network connecting an ESP8266 module in each circuit. Upon receiving this signal, the server circuit then switches

the server circuit’s LED on.

We will describe how to build and program a server and client circuit, which you can replicate for additional nodes.

In our example, we will illuminate some LEDs for our "ON AIR" signage, however, you could use the output to meet your needs. For example, you could trigger a relay module to control 12V devices, and the like.

We will also include the 3D print files that we used for our "ON AIR" enclosures, which you can easily modify for your application.

USER PRESSESPUSHBUTTON ON THE

CLIENT BOARD

CLIENT BOARD LEDSTURN OFF

CLIENT BOARD LEDSTURN ON

SERVER BOARDRECIEVES THE SIGNAL

SERVER BOARDRECEIVES THE SIGNAL

SERVER BOARDLEDS TURN OFF

SERVER BOARD LEDS TURN ON

ARE LEDSON OR OFF?

IF LEDS ON

IF LEDS OFF

CLIENT BOARD SENDSA SIGNAL TO SERVER

BOARD THROUGH WiFi NETWORK

CLIENT BOARD SENDS A SIGNAL TO THE SERVER

BOARD THROUGH WiFi NETWORK


PROJECT


FEATURES:

• 802.11 b/g/n

• WiFi Direct (P2P), soft-AP

• Integrated TCP/IP protocol stack

• Integrated TR switch, balun, LNA, power amplifier and matching network

• Integrated PLLs, regulators, DCXO and power management units

• +19.5dBm output power in 802.11b mode

• Power down leakage current of <10µA

• Integrated low power 32-bit CPU could be used as an application processor

• SDIO 1.1 / 2.0, SPI, UART

• STBC, 1×1 MIMO, 2×1 MIMO

• Flash: 4M

• A-MPDU & A-MSDU aggregation & 0.4ms guard interval

• Wake up and transmit packets in < 2ms

• Standby power consumption of < 1.0mW (DTIM3)

ESP8266 PINOUT ››

PIN DESCRIPTION IC INTERNAL PIND0 I/O, Interrupt, PWM, I2C GPIO16D1 I/O, SCL of I2C in default mode GPIO5D2 I/O, SDA of I2C in default mode GPIO4D3 I/O, Pull-up and enter flash mode at low power GPIO0D4 I/O, Pull-up GPIO2D5 I/O, SPI clock GPIO14D6 I/O, SPI MISO GPIO12D7 I/O, SPI MISO GPIO13D8 I/O, Dropdown, SPI, Default Slice Selection (SS) GPIO15A0 AD input, 0-3.3V ADC

ESP8266 WIFI MODULE

RIGHT ►XC3802 WiFi Mini ESP8266 Main Board from Jaycar

The main board of the project is based on the ESP8266 WiFi module (Module ESP-12E Wemos). It is a self-contained system-on-chip (SOC) with an integrated TCP/IP protocol. The module comes pre-programmed with an AT command set firmware.

The board enables electrical circuits to communicate with each other and/or communicate with other devices that can access the same WiFi network. It is capable of acting as an access point server or as a client that can be connected to other access points, such as home routers.

The module’s on-board processing and storage capability allows it to be integrated with 11 general-purpose input/output (GPIO), and has an analogue-to-digital converter (ADC). The WiFi antenna is highly sensitive and can be found at the side of the PCB (printed circuit board).

The design of the circuit has a high degree of on-chip integration and hence exhibits minimal external circuitry, including the front-end module. The tiny board is designed to occupy minimal PCB area (approximately the size of a coin). Overall, this module is extremely maker-friendly, particularly as it is breadboard-compatible with the addition of a few pins.

◄LEFTTesting the client board's current draw.


PROJECT


The Build:››PREPARATION

If not done so already, solder the header pins onto the ESP8266 modules so that they can fit into the breadboard.

Attach the battery holders to the 2-way screw terminals (before inserting the batteries in them).

Note: To avoid damage to the ESP8266 module, do not insert the batteries during the assembly stage. The modules will be powered after programming (later). This is to avoid connecting the module to the battery and laptop simultaneously, and therefore, applying too high a voltage for the module to withstand.

Follow the circuit diagrams and instructions to wire your Server and Client boards.

SERVER CIRCUIT

The anode of the LEDs on your server circuit go to pin 5 (D5) on the ESP8266.

CLIENT CIRCUIT

The anode of the LEDs on your server circuit go to pin 3 (D3) on the ESP8266.

The pushbutton connects across the breadboard divider such that the upper and lower legs are not connected.

The leg on one side of the pushbutton connects to pin 5 (D5) of the ESP8266.

PARTS REQUIRED FOR 1 X SERVER & 1 X CLIENT: JAYCAR ALTRONICS CORE ELECTRONICS2 x Wi-Fi Mini ESP8266 Modules XC3802 Z6381 ADA2471

4 x 5mm Red LEDs (Or your preferred colour) ZD0150 Z0800 COM-09590

1 × 10kΩ Resistor* RR0596 R7582 COM-10969

2 x 100Ω Resistors* RR0548 R7534 CE05092

1 x Tactile Pushbutton SP0600 S1120 FIT0179

2 x 4xAA Battery Holders PH9200 S5031 FIT0079

2 x 2-Way Screw Terminals HM3130 P2040 PRT-08432

8 x AA Batteries SB2425 S4955B CE04629

RIGHT (INSET) ►Client with Enclosure.

ABOVE ▲Server with Enclosure.

* Quantity shown, may only be available in packs. Breadboards and prototyping hardware is also required.


PROJECT


Add the ESP8266 library. Tools menu › Board: › Board Managers, then type Esp8266 and install the latest version of “esp8266 by ESP8266 Community”. ››

The leg on the opposite side of the pushbutton goes to the negative rail via a 10k resistor.

The other leg of the pushbutton switch on the same side connects to the 5V rail.

PROGRAMMING

Now, most of the hardware components are connected, this coming section will outline the steps required to program the ESP8266 board.

ESP8266 CONFIGURATION

One of the features of ESP8266 board is that it can be programmed using Arduino IDE, without the need for an additional Arduino adapter board. The configuration steps are:

OPEN THE ARDUINO IDE

Add the ESP8266 to the board manger. File menu › Preferences, then add the link http://arduino.esp8266.com/stable/package_esp8266com_index.json to the additional boards manager URLs.

Note: For our application, we added a 100Ω resistor to limit the current to the LEDs. You may need to use a different resistor value depending on the LEDs you use.

RST

A0

D0

D5

D6

D7

D8

3V3

TX

RX

D1

D2

D3

D4

GND

5V

RESETD1mini

RST

A0

D0

D5

D6

D7

D8

3V3

TX

RX

D1

D2

D3

D4

GND

5V

RESET D1 mini

ABOVE ▲Client Circuit Diagram.

BELOW ▼Server Circuit Diagram.


PROJECT


››Based on the “ESP8266 WiFi Mini” datasheet, we need to select the “LOLIN(WEMOS) D1 R2 & mini” model type. Go to the Tools menu › Boards: › and select LOLIN(WEMOS) D1 R2 & mini.

Next, Tools menu › Upload Speed › 115200

Now the ESP8266 is ready to be programmed.

THE CODE

The code is available to download from our website and is commented appropriately.

The coding section is divided into three steps:

1. A temporary code to be uploaded to get the IP assigned for each module.

2. Upload the server code to the server module.

3. Upload the client code to the client module.

GET IP CODE

When the ESP8266 board is connected to an access point router, the router assigns a random IP to the module. This IP can be thought of as the address of the board. To be able to communicate to this specific module, this IP is needed to be known. Thus, this code will be uploaded to each board, then the IP of each board will be saved to be used later.

The first part of the code adds the ESP8266.h library, which enables us to use the ESP8266 functions.

Add the username and the password of the existing WiFi network.

Initiate the serial monitor and specifying the transfer baud rate.

Initiate the WiFi connection.

//Include the library

#include <ESP8266WiFi.h>

const char* username = “your_network”;

//Insert the WiFi network username

const char* password = “password”;

//Insert the WiFi network password

void setup() {

Serial.begin(115200);

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PROJECT

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These two IPs will be inserted later in the server and client code to enable them to communicate with each other.

SERVER CODE

This code will be uploaded to the ESP8266 board that will perform as a server. Similar to the previous code, there are some variables that will need to be inserted. Those variables are the username, password and the IP of the client board (obtained after uploading the previous code to it).

Firstly, the library that enables the ESP8266 functions to be employed is added to the Arduino sketch.

Next, the variables that are to be used are identified. Also, a number that is to be assigned to the port to transfer the data is identified. This number can be anything (we chose 80).

Add the username and the password of the existing WiFi network.

Initiate the serial monitor and set the baud rate to 115200. ››

//Include the library

#include <ESP8266WiFi.h>

int led = D5;

const char * host = “192.168.1.106”;

const char* Commands_Reply;

WiFiServer server(80);

const char* username = “your_network”;

const char* password = “password”;

void setup() {

Serial.begin(115200);

Print the IP of the ESP8266 board on the serial monitor

Connect the module to the computer through the USB cable.

From Tools menu › Port: › COM13.

Note: The port number will change depending on the port the board is connected to. In our case, it is port COM13.

Upload the code twice (for each ESP8266 board).

Open the serial monitor and save the IP somewhere.

Serial.print(“Attempting to connect to SSID”);

WiFi.begin(username, password);

while (WiFi.status() != WL_CONNECTED) {

Serial.print(“.”);

delay(1000);

}

Serial.println(“”);

Serial.println(“WiFi connected”);

Serial.println(“IP address: “);

Serial.println(WiFi.localIP());

}


PROJECT


››Connect to the WiFi and print the local IP of the board (it should be the same as the one obtained from uploading the “Get IP” code).

Start the server.

Check if the client is connected to the server.

Check if the client has sent any data.

Read the data received from the client and clear the buffer.


Serial.println

(“Server------------------------”);

Serial.print(“Configuring access point”);

Serial.print

(“Attempting to connect to Network”);

WiFi.begin(username, password);

while (WiFi.status() != WL_CONNECTED) {

Serial.print(“.”);

delay(1000);

}


Serial.println(“WiFi connected”);

Serial.println(“IP address: “);

Serial.println(WiFi.localIP());

server.begin();

Serial.println(“Server started”);

WiFiClient client = server.available();

if (!client) {

return;

}

Serial.println(“Server-----------------”);

Serial.println(“New client”);

Serial.print(“From client = “);

while(!client.available()){

delay(1);

}

String req = client.readStringUntil(‘\r’);

Serial.println(req);

client.flush();

This part of the code, the server receives the data from the client to turn the LED ON or OFF and accordingly.

UPLOAD THE CODE


Tools menu › Port: › COM13.


Upload the code to the server ESP8266 board.

Disconnect the board from the computer.

Now we have the code uploaded to the server board, the same steps will be repeated for the client (yet, obviously, with different code).

CLIENT CODE

This section will outline the various sections of the server code.

The IP address that will be inserted here is the IP of the server.

if (req.indexOf(“LED_On”) != -1){

Commands_Reply = “LED Status : On”;

Serial.print(“Server send = “);

Serial.println(Commands_Reply);

client.print(String(“GET “)

+ Commands_Reply + “ HTTP/1.1\r\n” + “Host: “

+ host + “\r\n” + “Connection: close\r\n\r\n”);

digitalWrite(led, HIGH);

}

else if (req.indexOf(“LED_Off”) != -1){

Commands_Reply = “LED Status : Off”;

Serial.print(“Server send = “);

Serial.println(Commands_Reply);

client.print(String(“GET “)

+ Commands_Reply + “ HTTP/1.1\r\n” + “Host: “

+ host + “\r\n” + “Connection: close\r\n\r\n”);

digitalWrite(led, LOW);

}

else {

Serial.println(“invalid request”);

client.stop();

return;

}

client.flush();

Serial.println(“Client disonnected”);

Serial.println

(“-------------------------------------”);



PROJECT


This part of the code handles the communication and sends the data to the server, establishing a connection with the server using the port number and IP...

...sending the commands to the server.

Check if the communication is established and whether there is a replay from the server.

UPLOAD THE CODE


From Tools menu › Port: › COM13.


Upload the code to the client ESP8266 board.

Disconnect the board from the computer.

Now we have the code uploaded to the client board. ››

WiFiClient client;

if (!client.connect(host, httpPort)) {

Serial.println(“Connection failed”);

return;

}

client.print(String(“GET “) + Commands + “

HTTP/1.1\r\n” + “Host: “ + host + “\r\n” + “Con-

nection: Close\r\n\r\n”);

unsigned long timeout = millis();

while (client.available() == 0) {

if (millis() - timeout › 5000) {

Serial.println(“>>> Client Timeout !”);

client.stop();

return;

}

}

Serial.print(“Server Reply = “);

while(client.available()){

String line = client.readStringUn-

til(‘\r’);

Serial.print(line);

}

This loop is to detect if the push button is pressed, save the number of presses and reset the counter if the number of presses is more than two. This allows the program to have the capability to determine whether to turn the LEDs ON (e.g. one press) or OFF (e.g. second press).

This part of the code turns the LED on and off, and sends the data to the server according to the number of presses.

const char * host = “the_IP_address”;

const int httpPort = 80;

const char* Commands;

int LED = D3;

int button = D5;

bool btn_press = true;

int con = 0;

if (digitalRead(button) == LOW) {

Serial.println(“Client------------------”);

Serial.print(“Send Command = “);

if (btn_press == true){

if (con >= 2) {

con=0;

}

con++;

switch (con){

case 1:

digitalWrite(LED,HIGH);

Commands=”LED_On”;

Serial.println(Commands);

send_commands();

break;

case 2:

digitalWrite(LED,LOW);

Commands=”LED_Off”;

Serial.println(Commands);

send_commands();

break;

}

btn_press = false;

}

}

else {

btn_press = true;

}

delay(100);

}


PROJECT


››TESTING

At this point, we have both of the circuits ready i.e. the server and the client, wired and programmed.

After we disconnect the modules from the computer, they will need a source of power to work on their own, and hence, are connected to their respective 6V battery holders. The positive of the battery is connected to the 5V pin, and the negative is connected to the GND pin.

Note: It is recommended not to exceed 7V due to the ratings of the voltage regulator on-board the ESP8266 module.

Now we have the completed project which operates such that:

• Pressing the push button connected to the client will turn the LED ON connected to it.

• Then the client module will send an “LED_ON” message to the server module through the WiFi network using the unique IP assigned to the server.

• The server receives the message and then, triggered by its program, turn its LED ON.

• By pressing the push button again, through the same mechanism, the program will count a repeated press, and turn both LEDs OFF.

Note: Due to the time required to both send and receive signals using the ESP8266 modules, there may be a small lag in communication.

ENCLOSURE

Finally, an enclosure was designed to both encase the server and client modules, as well as add the aesthetics of an “ON AIR” sign that is lit by the circuits’ LEDs. The enclosure was designed using TinkerCAD, a free, web-browser based program that is easy to use without the need for much CAD (computer assisted design) experience. For the design to meet our criteria, the “ON AIR” sign was printed using transparent filament to enable the LED light to pass through the enclosure.

WHERE TO FROM HERE?

A few examples of how this project may be scaled include:

• The addition of more client nodes that enables even more “ON AIR” lights to be positioned around the studio

• The replacement of the hardware trigger (e.g. pushbutton) with a software trigger (e.g. a graphical user interface on a web server) whereby these circuits may be triggered through any device that may access the WiFi network (e.g. computer, tablet, mobile phone, etc.)

• Through port forwarding, the ESP8266 module may be configured to allow this system to be triggered from anywhere in the world through the internet.

• Use a more powerful battery (Li-ion or Lead Acid) to control an LED Strip or something more "visible".

• To add additional artistic flair, or to customise the mounting or aesthetics of the “ON AIR” 3D printed sign (TinkerCAD working files will be included on our website for you to download)

Note: TinkerCAD can be downloaded for free at www.tinkercad.com. You will also find useful training guides on Fraser's website www.integratedstem.com.au

Whilst this project was focused on the design of an “ON AIR” sign for our recording studio, the ESP8266 module has almost limitless potential for makers looking to create a convenient, wireless control method for their own IoT (Internet-of-Things) projects.

Any of the client nodes created may trigger a circuit alternative to the LED circuit used in this project. For example, a simple relay circuit could be triggered by the client to turn on any household device (stick to low voltage only for the sake of safety i.e. below 50V). The possibilities of this module are limited only to your imagination – get out there and experiment with IoT for yourself! ■

WANT MORE?For the code and 3D print files, or to discuss this project, visit:https://diyode.io/036brgb


PROJECT

https://diyode.io/036brgb


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PROJECT: Arduino® Keyboard Emulator

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Arrival dates of new products in this flyer were confirmed at the time of print but delays sometimes occur. Please ring your local store to check stock details. Occasionally there are discontinued items advertised on a special / lower price in this promotional flyer that has limited to nil stock in certain stores, including Jaycar Authorised Resellers. These stores may not have stock of these items and can not order or transfer stock. Savings off Original RRP. Prices and special offers are valid from catalogue sale 24.06.2020 - 23.07.2020.

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SIMON SAYSHandheld Electronic Game using ArduinoWhen a maker wants to teach his 7 year old great-nephew electronics and have fun at the same time, he turns an old classic game into a handheld game for hours of fun.


FEATURE


››Miles created a breadboard kit that builds a retro memory game, then turned it into a hand-held version on a PCB. The game is based on the “Simon” electronic game of the 1980s where the player has to repeat the sequence of lights randomly chosen by the brains of the game (in my case an ATmega328). I used EasyEDA and JLCPCB to create the schematic, design and manufacture the PCB.

Thank you for submitting your project to us via our website. Can you tell our readers a little about yourself and how you got into electronics?

I’ve been a software engineer forever (well, 30 years seems like forever). I got into electronics about 5 or 6 years ago when I started to watch Ben Heck and Dave Jones on YouTube. They are great ambassadors for electronic hobbyists and their enthusiasm is contagious.

A friend bought me a couple of intro books to electronics and I bought an Arduino and some components, including a bunch of 8x8 LED matrix’s and some MAX7219CNG IC’s. I was able to use my programming skills with the Arduino and loved the fact that I could build something physical.

Back in 2017, I submitted a project to DIYODE that I made for my godson and was lucky enough to win the Editor’s Choice award, which I put toward buying an oscilloscope – an amazing Rigol DS1054Z.

Oh yes, the Sensory Board project of yours that we published in Issue 4 (Oct 2017) was amazing. It seems like your Nephew is lucky to have a Great-Uncle with electronics prowess. You mentioned you made him a Theremin before building this Simon-like game to teach him about electronics.

My great-nephew Blake, who is 7 years old, has always been interested in how things work and making things, and his mum had bought him a clip-together electronics kit that he really enjoyed. I thought he might like to build a “real” electronics circuit with some raw components and a breadboard. The Theremin was quite basic (an oscillator IC, LDR and a speaker) and not too many jumper wires, but was really interactive, using a torch or your hand to light or cover the LDR and change the tone coming from the speaker.

It’s great to be able to build circuits using commonly available components that have practical outcomes that kids can engage with. What was the inspiration for progressing from the Theremin to your Simon game?

I wanted Blake’s next project to be a bit more challenging, but also rewarding, so I was thinking that some sort of game that kept a score and he could try to beat his best score, or challenge his mum or friends to see who could get the highest score. I remembered playing “Simon” when I was around his age and thought that was something that I could prototype using an Arduino. The initial game-play I developed didn’t seem quite right, so I turned to Google & Wikipedia, to find out what the original gameplay was. https://en.wikipedia.org/wiki/Simon_(game)

It is such a simple but addictive game, and we like your approach to ‘gamify’ the project to keep Blake entertained. Can you give us an overview of how your circuit works?

The circuit is pretty simple, 5 tactile switches, 5 related LEDs (with current limiting resistors), the score-module and one speaker.

• The player initiates the game by pressing the start switch (white LED),

• This resets the score module to “00”,

• A random coloured LED is then lit and an associated tone is played, the coloured LED is then unlit,

• The player must then press the button under the LED that was lit, ››

MILES HITCHENSoftware Engineer and

Electronics Hobbyist.

https://github.com/milesee/

Blake building the Theremin project.

Theremin build.


FEATURE

https://en.wikipedia.org/wiki/Simon_(game)

https://github.com/milesee/


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FEATURE


››• If they press the wrong switch then the game ends.

• If they press the correct switch then the score module is clocked and the score increases by 1.

• A new random colour LED is then added to the sequence, and each one lit and associated tone played.

• The player must press the associated switches in the correct sequence, with each correct switch press increasing the score by 1 (the length of time the tones are played for increases as the player reaches specific scores).

• This continues until the player presses the wrong switch or they reach a score of 99, when a winning tune is played through the speaker.

On the PCB version I increased the number of 7-segment displays so that the score could go higher than 99.

Tell us more about your small 7-segment display PCB.

It’s used to keep the score and makes use of some 4000 series ICs (CD4026BE) that are combined decade counters and 7-segment display drivers, I had these components left over from a previous project. Besides power, the module only needs a few pins to drive it.

Did you find the game-play code online, and were there any modifications you needed to make?

Although I could probably have found some code online, being a software engineer, I wanted to write it from scratch myself. There were a few tricky points:

RANDOMLY GENERATING THE LIGHT SEQUENCE: I looked at a couple of approaches, but finally settled on using the Arduino’s millis() function (the number of milliseconds since the Arduino was turned on). When the player presses one of the tac switches, we can get the value of millis() Modulus 4, to give a pseudo-random number between 0 and 3, using this as the index for the next light in the sequence. This seems to work well.


FEATURE


SOUNDS: I also wanted to use the tones from the original game (as these were chosen to always be harmonic, whatever order they’re played in).

So I needed to do some more googling to work out how to convert the notes to a frequency that could be used with the Arduino tone() function.

Also, on the topic of audio, the original game had a pretty poor note sequence when the player completed a level, so I improved on that by using some audio code from: https://dragaosemchama.com/en/2019/02/songs-for-arduino/

Great! Good advice for any of our readers wanting to develop their own game on their Arduino. What other challenges did you need to overcome to get the prototype to work?

Low power consumption on the ATmega328, so that it could use two or three 1.5v cell batteries. I was able to achieve this by modifying the board file so that the fuse settings for the Brown-Out value was lowered.

I didn’t want (or need) the 16MHz clock, so it was necessary to download a board definition for the 8MHz internal clock. Unfortunately, I bought some ATmega328-U’s (rather than the P-PU’s) which aren’t supported by the Arduino IDE without some modifications to one of the config files.

Those letters at the end of the part number can make all the difference sometimes. Your breadboard prototype was obviously well received by Blake in order to motivate you to turn it into a handheld PCB?

To be honest, I enjoyed playing the prototype version so much, that I wanted to convert it to a handheld PCB version, for myself and to give as unique gifts.

DIY Birthday presents! What steps did you take to go from prototype to PCB design?

I’ve used a couple of schematic/PCB design solutions in the past, RS DesignSparkPCB, EasyEDA, Aisler & JLCPCB. I’ve settled on using EasyEDA & JLCPCB to create a schematic, PCB and get it manufactured.

I like using EasyEDA as it’s quite intuitive, has a simple interface and can be used in a browser, so you only need access to the internet to work with it, it also has a massive library of schematic/PCB parts and a good editor for creating new parts. I did find initially that I had no idea where to start (as I had no experience of creating schematics or PCB’s), but I found a good YouTube video that goes through the basics: https://youtu.be/_3jFsNffzxQ.

Great! It’s so easy for makers to be able to design and source their own boards now. In Issue 34 we started teaching our readers how to use EAGLE.

Tell us, what design challenges did you need to overcome with your PCB design, and how did you find the service and quality of the board from JLCPCB?

Ergonomic component layout and track layout is always more time consuming than you’d expect. Getting the right ergonomic and aesthetic layout for the components took some time. I used some Veroboard to help with the layout (it’s a lot easier and gives a better feel for the final product than laying out in the PCB design software). Also, I’m no expert at laying out the PCB tracks, and although EasyEDA has the capability to auto layout the tracks, the results are rarely as good as a human can achieve with a bit of time and patience. As I use a lot of through-hole components that have a 0.1” pin pitch, I tend to use a display grid of 0.1” and a snap grid of 0.01” (or 0.254mm).

I’ve made quite a few boards using JLCPCB. It integrates well into EasyEDA and I’ve always found their service and board quality great. Their customer service is pretty good too, they even allowed me to change the board colour after submitting it for manufacture. ››


FEATURE

https://dragaosemchama.com/en/2019/02/songs-for-arduino/


››The auto track layout feature in EasyEDA and others is handy, but agreed, we can’t rely on it to get it 100% correct. Is this the first time you have used an ATmega328 in a project, and how did you go about programming it?

I’ve used a standalone ATmega328 in a number of projects. I program it using the Arduino board and IDE, then I’ll burn it onto a new chip using a breadboard and the Arduino as an ISP. The Arduino website has a great article on this covering both the use of an external and internal clock: https://www.arduino.cc/en/Tutorial/ArduinoToBreadboard

Excellent! It can be a little daunting knowing how to program a 328. Do you have any plans to make an enclosure for your PCB design?

I designed the component layout to be seen, I think it gives it a retro-look, I know it’s not particularly practical, but I think it looks good. I might look at creating a clear case so that the components are protected, but still visible.

Agreed. Hiding the electronics mean that you can’t admire your handiwork. If you were to start the project again, would you do anything differently?

The circuit has no reverse voltage protection, so I’ve been looking into that. I am considering the approach here that uses a FET (https://www.radiolocman.com/shem/schematics.html?di=588375) This would result in a minimal voltage drop (much lower than a

Using Veroboard to workout the ideal component placement.

simple diode approach). Also, I’d remove the red power indicator LED as this is redundant due to the 7-segment displays being lit.

Using a FET is an interesting approach instead of a diode that would reduce battery life. Is there anything else about your project that we haven’t covered that our readers should know about?

The PCB version has a few upgrades from the prototype. There’s a “Repeat Sequence” switch that will repeat the sequence of LEDs, if the player hasn’t pressed one of the coloured LEDs. Also, I’ve updated the code so that there’s a “winning” tune played at various milestones e.g. every 5 sequences.

As a teaching/learning tool, the breadboard/prototype project provides a good opportunity for troubleshooting as it’s quite easy to wire things up incorrectly, especially around the LEDs and tac switches. Blake had a few issues with this, but he persevered and figured out where he went wrong, and I’m very proud of him for sticking with it. The feeling of achievement when you complete something that is challenging is definitely worth the effort.

Some great additions there, and we agree, the thrill of getting a circuit to work after a little troubleshooting is a good feeling. If our readers wanted to make one of these for themselves, can they get the schematic, board design, and code?

I have created a GitHub repository for the Arduino code: https://github.com/milesee/arduino_simon_game

I've also made the EasyEDA projects for the Simon Game and Scoreboard Module public:

SIMONGAME: https://easyeda.com/milesee/simon_copy

SCOREBOARD MODULE: https://easyeda.com/milesee/seven-segment-counter_copy

We’ll put the files on our website for our readers to access, thanks a million. Are you working on any other projects for yourself or your nephew?

I’ve been thinking of building a simple 3-wheel robot that has collision detection using the sonic distance measuring modules. I know there are a lot of kits out there already, but I’m interested in building one from scratch.

We’re sure Blake would be over the moon to build and play with a robot. We wish you all the best and thank you for sharing your project build with us. ■

WANT MORE?For the code and PCB files, or to discuss this feature, visit:https://diyode.io/036myns


FEATURE

https://www.arduino.cc/en/Tutorial/ArduinoToBreadboard

https://www.radiolocman.com/shem/schematics.html?di=588375

https://github.com/milesee/arduino_simon_game

https://easyeda.com/milesee/simon_copy

https://easyeda.com/milesee/seven-segment-counter_copy

https://diyode.io/036myns


Dream like a child. Build like a machine.

www.altronics.com.au | 1300 797 007

DIYODE-Back_Cover_v1.indd 3 6/06/2017 1:02 PM

http://www.altronics.com.au

http://www.altronics.com.au

PERSISTENT POWERArduino-based

High Capacity 12V UPS

BUILD TIME: 4 HOURS (+ 3D PRINTING TIME) DIFFICULTY RATING: INTERMEDIATE

With broadband replacing fixed-line phones, keeping the power on during blackouts is essential, as the horrific bushfire season in Australia showed us recently. This UPS is designed to power your modem/WiFi router, providing essential phone and Internet service for several hours.

Impressively, it is able to supply up to 5A for over an hour, and can also supply high short-term peak currents to run devices such as a 12V compressor fridge.

THE BROAD OVERVIEW

Our 12V UPS is designed to go in series with the 12V power supply that powers the device you want to keep running during a blackout, such as a broadband router.

The UPS uses the newest LiPoFE4 lithium battery technology (they don’t catch on fire as Li-ion can), which is charged thanks to the onboard Boost module.

We use an Arduino Pro Mini running in a low power mode and with its power LED removed to conserve power, a colour OLED display, and solid-state MOSFET switches.

A custom-designed 3D printed enclosure rounds out the project.

Build this 12V uninterruptible power supply to keep your broadband and other important tech running during a blackout.

GEOFF COHENWriter, programmer, and maker.

thingiverse.com/geoff_cohen/designs


PROJECT

http://thingiverse.com/geoff_cohen/designs


HOW IT WORKS

CHARGER / BOOST MODULE

With a (nominal) 12V input to the UPS and the Boost Module set to 13.6V output, the Boost module powers the load and also charges the LiFePO4 battery. The boost module works with any input voltage between 10.5V and 13V. You can also power the UPS from 24V (or vehicle use at 14.2V) by replacing the 6A Boost module with a 6A Buck module (we use one of our UPS’s this way to power a 12V Car Compressor fridge when parked for a while).

The Boost module is isolated from the output and battery by MOSFET Q4 (refer to the schematic) acting as a very low loss pseudo-diode. We initially used a Schottky diode to isolate the battery from the input, but with over 500mV loss at 5A, it ran too hot to touch, and, as we had quite a few spare NDP6020 MOSFET’s, we modified our design to use one as a pseudo-diode. When checked, we measured a very small 54mV drop and

only a 2°C increase in temperature at 5A. We even tested it at 10A for 30 seconds with no ill effects, although this is outside the continuous ratings for the Boost module - using a higher capacity boost module and a bigger battery (or two in parallel) leaves the way open for a higher current UPS version with minimal changes needed.

BUCK MODULE: A switching regulator with output voltage LOWER than its input

BOOST MODULE: A switching regulator with output voltage HIGHER than its input

USING AN ARDUINO TO CONTROL A UPS

Normally, an Arduino uses too much power for use in a UPS, but the Low Power Library by Rocketscream (https://github.com/rocketscream/Low-Power) has some extremely low power sleep modes. With one simple modification, the sleep current of your Arduino drops from 3mA to 25μA. ››


PROJECT

https://github.com/rocketscream/Low-Power


››As an example of how useful this is, when your UPS battery is nearly flat (approximately 1.5% capacity left in our 7AH battery). 3mA would exhaust a nearly flat battery in just one day, however, by just removing the Arduino Pro Mini’s power LED, the same, nearly flat, battery would last over 2 months (hopefully mains power won’t be out that long).

In our UPS, when it’s battery powered, if the battery is nearly flat and the voltage drops below 12V, the Arduino Pro Mini first isolates the battery (by turning off MOSFET Q1) then the Arduino switches to low-power SLEEP mode, consuming only 25μA, preventing the battery going completely flat for months. The Arduino code then periodically (once a second) wakes up for approximately 200 microseconds, checks to see if the input power is back on and resumes normal operation if it is. Using this simple method of operation only increases the average SLEEP power used by 0.02% percent.

We selected an Arduino Pro Mini for this project. Having no USB Port that would be drawing several mA, it is one of a few Arduinos that can run in very low power mode, drawing only 25µA in sleep mode. The only change needed is to remove the Arduino board’s power LED.

ARDUINO PRO MINI LOW POWER DETAILS

ATMEGA328P PRO MINI POWER INPUT MODE CURRENT

ORIGINAL – UNCHANGED RAW Pin Active 21mA

ORIGINAL – UNCHANGED RAW Pin Sleep 3mA

NO POWER LED RAW Pin Active 18mA

NO POWER LED RAW Pin Sleep 25μA

NO POWER LED, NO REGULATOR VCC Pin Active 13mA

NO POWER LED, NO REGULATOR VCC Pin Sleep 6 μA

We also encountered problems on some Arduino compatible boards with their internal voltage regulator dying when more than 12V was applied to the RAW input, so we used seven series-connected 1N914 diodes to drop the RAW voltage from 13.6V down to (approximately) 9V and have had no more problems. We didn’t use a Zener as they tend to not work at very low currents, in this case, 25μA in SLEEP mode.

MOSFET (Q1)

MOSFET (Q1) needs a small heatsink because, when charging a very flat LiFePO4 battery, the internal diode in MOSFET Q1 forward conducts and produces some heat. Only a small heatsink is required. We used a couple of Raspberry Pi adhesive heatsinks,

but any similar sized one will work, even a 12mm x 12mm piece of Aluminium screwed to Q1 would work.

Once the battery is moderately charged, this diode stops conducting, then the battery charging current is limited to 3A, using PWM (Pulse Width Modulation) control from Arduino output D3. Q2 acts as a level converter with resistors R5 and R6 limiting the gate voltage (VGSS) to Q1, as it’s rather low at only 8V. This method is also used with R19, R20, Q3, and Q4.

MEASURING VOLTAGE AND CURRENT

As the Arduino can't measure negative voltages, we used three different earth (or more accurately, 0V reference) points: the 12V and Boost GND input, battery GND, and output GND. Of course, at full current there is only 0.025x5 or 125mV difference between each one. The battery current is not measured directly, but calculated from the difference between input and output current. You can examine the code in function readAllAnalogInputs() (in file DIYODE-12V-UPS-Mk2.ino - near line 470). The voltages are measured via the 15:1 voltage dividers (R3/R4, R8/R9, R11/R12) into the Arduino board’s analog inputs, with some maths being performed to allow for the slight difference between the three ground reference points.

LIFEPO4 BATTERY

We were pleased when we noticed Jaycar had added a 12V/7AH LiFePO4 battery to their products. LiFePO4 batteries are much safer, they don’t catch fire (unlike Li-ion), and having an internal BMS (Battery Management System) makes charging much simpler, with each internal cell receiving a balanced charge. LiFePO4 cells are also relatively forgiving and can be fully charged by any voltage between 3.4V and 4.2V per cell, although 3.4 - 3.6 are considered optimal. The BMS should also prevent damage to the LiFePO4 battery if it ever goes completely flat, but minimising that risk is always a better option.

COOLING FAN OPTION

Although we haven’t needed one yet, we have allocated space for a 40mm cooling fan that you can add if you are running high loads (eg. 6A) 24/7 or live in hot climates, such as the NT or FNQ.

OLED SCREEN

A 0.96” I2C OLED display module is used to show exactly how the UPS is performing, displaying voltage and current for the input, battery and output.

Note: We are currently adding code to show the battery charge %, which should be available by the time we go to print. ››


PROJECT


R050

R1

R050

R2

20K

R4

1M5

R8

100K

R9

100K

R16

470Ω

R19

220Ω

R18

100K

R12

300K

R11

300K

R3470Ω

R5

470Ω

R6

220Ω

R10470Ω

R20

1K R71K

R13

1K

OUT -

BatteryLiFePO412V/7AH

12C OLED

MOSFET B

attery Switch

MOSFET Diode

Boost Module

12V/6A

OUT +

Q1IRF9540/N

DP6020P

Q4IRF9540N

DP6020P/

F1Fan 12V (Optional)

Q22N7000

Q32N7000

2D

1

GND

GND

GND

GND

RAW24232120191817

GND

GND

IN+

43IN

-

OUT+1

+-2

OUT-

VCCA3A2D3

A1A0

SDA 43

313233

2

1

SCLA4A5A6

GND

+5V

To A3

GND

+13.6V

0V

GND

To A1

To A6

To A2

To A0

To D3

D1D2

D1D4

D5

D6D7

R050

R14

R050

R15

IN -

IN +

11-14VDC

GND

GND

GND

Input0V ref

23

1

DS

G

DS

G

Arduino Pro Mini

Battery -

3S

G

The 7 x 1N914 diodes low

er the RAW

input from ~13.6V to ~9V

to prevent damage to som

e voltage regulators on the Arduino Pro M

ini.

Note: W

e recomm

end you add a fuse on this inpu t.

BatteryGN

D

Power In

Detection

Battery +

OLED Socket

Input GND


PROJECT


The Build:››Building the UPS is relatively straightforward; the LiFePO4 battery rests on the baseplate, and is held In place by both the 3D printed battery clip screws and two baseplate battery end support walls. The Boost module and protoboard (with Arduino Pro Mini, OLED display, and all other components) are screwed to this battery clip, with the two input and two output wires clamped to their strain relief mounts with small wire ties.

As there are so many different connectors that could be used, we left the inputs/outputs as flying leads, rather than mounting connectors on the 3D case that would only be the correct connectors in a very small percentage of cases. With flying leads, you just need to solder on an input and an output connector to suit your application. The UPS is simply plugged in between your original 12V source and the device being protected/powered by your UPS. Plus, if there is ever a problem with your UPS, merely unplug it and use your 12V device as originally setup, without any UPS protection.

PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 x Arduino Pro Mini or Compatible - Z6222A 018-MINI-05

1 x FTDI- USB Serial 3.3V/5V XC4464 Z6225 DFR0065

2 x P-Ch Power MOSFET ZT2467 Z1543 COM-12901

2 x 2N7000 N-Channel FET ZT2400 Z1555 CE07138

1 x 40 Pin Socket Header Strip HM3230 P5384 PRT-00115

1 x 40 Pin Pin Header Strip HM3212 P5430 ADA2671

1 x Solder-able Breadboard - H0701 -

1 x DC-DC-Boost Converter (150W) - - 018-DCDC-BOOST-150W

1 x 12V/7AH LiFEePO4 Battery SB2210 - -

1 x OLED Screen 128x64 - Z6525 TOY0007

1 x Mini Heatsink* HH8584 H0603 FIT0367

1 x Insulated Female Spade - Red* PT4525 H1810 -

1 x Insulated Female Spade - Blue* PT4625 H1806 -

2 x M3 Countersunk Bolt or Small Self-tapping Screws (Over 15mm Long)* HP0626 - -

8 x M3 Bolts or Small Self Tapping Screws (8-12mm length - not countersunk)* HP0403 H3120A FIT0061

1 x Heatshrink Tubing Pack WH5520 W0882 ADA1649

4 x 50mΩ SMD Current Sense Resistors^ Element 14: 3285931

* Quantity shown, may be sold in packs. ^ The current sense resistors are available from various online electronics retailers. Search for PCS2512DR0500ET.


PROJECT


CONSTRUCTION

The first thing to decide is, do you want to remove the Arduino board’s power LED for the best low power performance. Locating the power LED is really easy - just connect the Pro Mini to your FTDI-USB Serial board (don’t forget to plug your FTDI into your computer), and you will see the Arduino board’s power LED turn on. Just mark it with a Texta, turn everything off and unsolder the LED. It’s possible to unsolder it with a regular single soldering iron, but a SMD de-soldering tool makes it much easier. Commercial units around $200 are available, or you could consider making Geoff’s SMD Desoldering Tool that uses two cheap USB soldering irons (https://www.thingiverse.com/thing:4460653). We recommend a pair of stainless tweezers to make removing the SMD LED from the tips much easier too.

Except for the Boost module, the Arduino board, MOSFETs, and all the other electronic components are soldered to a protoboard.

As there are several versions of the Arduino Pro Mini, with slightly different pinouts for A4, A5, and A6 (some not even on a 0.1” grid), to fix this problem we’ve used flying leads to connect A4, A5, and A6, simply making our own 1 and 2 pin connectors from sections of 40-pin socket header strip (the images show you how we did this). The heatshrink tubing isn’t essential, but is good practice and will prevent any future problems with broken wires.

Note: Just remember that using proto-links on a working power supply may result in 'unfavourable' faults if one becomes loose or disconnected!

As the voltages across the 25mΩ current sense resistors (R1/R2 and R14/R15) are quite low (125mv @ 5Amps) we used heavy gauge 1mm tinned copper wire for all earth bus connections to maximise accuracy (we stripped the wire from a length of old 1mm Twin and Earth cable). This heavy wiring also acts as a heatsink, further reducing any heating of the SMD current sense resistors.

We could have used 0.025Ω (25mΩ) resistors for the current sense resistors, as they are 2W rated and the maximum power dissipation is estimated as 0.625W (625mW). However we chose to use two 50mΩ in parallel for better heat dissipation and lower temperature.

Before installing the Boost module, we connected it to our 12V source and adjusted the Boost modules output to exactly 13.6V. This provides around 97% capacity compared to charging at 14.6V, and is much less likely to hurt any 12V electronics on the output side.

Note: You will need to bend the leads on your 2N7000's to match the protoboards 0.1" grid. ››

Note: We incorrectly used BS170 FETs for Q2/Q4 on the photographed build. The Source and Drain pins are reversed compared to the correct 2N7000 FETs. Unfortunately, we didn’t notice as we always check component pinouts with our TC1 Multi-Function Tester before soldering. Both types will work, just remember the pins are reversed.


PROJECT

https://www.thingiverse.com/thing:4460653


››THE CODE

Firstly, if not in your Arduino Library, you will need to install these libraries by selecting Sketch > Include Library > Add .ZIP Library: https://github.com/rocketscream/Low-Power https://github.com/adafruit/Adafruit_SSD1306

The code for this project can be downloaded from our website.

Note: If you have both an FTDI USB-Serial board and Arduino Pro Mini with the same polarity FTDI programming connectors don’t despair, just do what we did, cut two 6-way lengths from your 40-way socket strip and solder them together to make an adapter.

We originally tried using the Arduino with interrupt driven code, but it just couldn’t switch fast enough. Our 300MHz Tektronix CRO showed BIG switching spikes, so we finally settled on a design with the battery always connected. Now, when the 12V input goes off, there is not the slightest sign of a switching spike. You can only tell the input 12V went off by looking at the display.

If you are really keen, you can even calibrate the voltage and current exactly by measuring it with an accurate meter and then adjusting vRefMultIn, vRefMultOut, vRefMultBat and aRefMultOut (In file DIYODE-12V-UPS-Mk2.ino, near line 121) so the values displayed on the UPS’s OLED display match your measured values. For extra accuracy, you can even display these values with 2 decimal point accuracy (at the cost of a smaller font) by changing the decimalPoints variable (around line 81) from 1 to 2. Just remember to change it back if you prefer the bigger fonts as we do. We used some existing sense resistors (of unknown accuracy), but using more accurate resistors (0.5% or 1%) makes extra calibration of current with aRefMultOut unnecessary.


PROJECT

https://github.com/rocketscream/Low-Power

https://github.com/adafruit/Adafruit_SSD1306


We have put in a lot of explanatory comments, so you should have minimal problems modifying our code.

TESTING

Initially, leave the battery (Brown & Blue wires) and output (Yellow & Green wires) unconnected, then supply between 10.5V and 13V to the input leads (Red & Black wires). You will see the OLED display turn on with three separate sections - the top section displays the output voltage and current, which should be close to 13.6V. The centre section shows the input voltage and current, and the lower section displaying the battery voltage and current. With only an input and no battery or output load, all currents should be close to zero. You can now connect the LiFePO4 battery, and unless the battery is fully charged, both input and battery will display some current flow, and if you disconnect the input power, the display will change to "On Battery".

With these tests completed, you can now reconnect the input power and also connect a load to the output e.g. NBN Modem. All three sections will display their respective voltage and current details, and the output will be powered with or without any input power. All that remains is to clip the top cover to the baseplate (sometimes a firm tap is needed to press the top cover's 20 recesses in place around the baseplate's 20 edge retaining clips.

Note: If the UPS is not needed for several months, remove the case top and unplug the battery to turn the UPS off.

3D PRINTED ENCLOSURE

We used PETG, but PLA would be OK for indoor use. We used support for the cover but it may be unnecessary, and it’s a real pain to clean out all the holes.

We’ve also provided two alignment clips that align the OLED display in the viewing window. If your Arduino has a male programming connector you may only be able to use the bigger alignment clip.

In our early designs, there wasn’t quite enough pressure to hold the top in place. We just warmed the top cover edges with a hot air gun,

pressed inwards, and let it cool (for our build, the cover is so tight we need to push a spudger in quite hard to separate the lid and baseplate). We have modified the design to minimise this problem with some extra reinforcing, both inside the top cover, battery clip, and around the baseplate edges.

Assembly is easy! First, place the battery on the baseplate, put the battery clip in place and use two countersunk M3 (or self-tapping screws) to hold everything together. Then use four screws to hold the Boost module in place, after removing the four spacers on the Boost module (only if it has some, of course). Then screw the proto-board in place and clamp the input and output wires to their strain reliefs. We recommend looking carefully at the pictures we have provided, which are the best way to check the correct orientation of all parts.

WHERE TO FROM HERE?

If you are handy with circuit board design, you could make a PCB for the project, which would make it much quicker to build and reduce assembly errors.

A few other ideas include:

• Modify the source code to show battery power/time/% left to run.

• Run two (or more) batteries in parallel so your UPS runs longer under battery power.

• Put in a bigger Boost (or Buck) module for higher power.

• Add an ESP-01 for telemetry and send UPS status to phone/PC etc.

• Experiment with higher output currents (10-15 Amps) by adding a heatsink for both NDP6020 MOSFETS and changing the current sense resistors. ■

WANT MORE? For the code and 3D print files, or to discuss this project, visit: https://diyode.io/036nmkc

BATTERY CLIP TOP COVER BASEPLATEOLED ALIGNMENT

CLIPS


PROJECT

https://diyode.io/036nmkc


JOHANN WYSSStaff Technical Writer

In this issue, we show you how to etch a PCB at home using the toner transfer method and ferric chloride etchant.

If you have been following our 'How to design a PCB using EAGLE' series in Issue 34 and Issue 35, you would have designed a square wave generator circuit board that you could send off to a circuit board manufacturer. This tutorial uses the same square wave generator circuit board design that we will etch at home instead.

You can certainly use your own circuit board design for this tutorial or download the square wave generator design from our website if you prefer.

HOW TO ETCH A PCBPart 1


PCBEASY


Being able to etch your own circuit board at home is a great skill to have. This can save you from having to make your complex circuit on a perfboard, or having to wait for weeks to get a board from a local or international circuit board manufacturer.

Many techniques exist for etching a Printed Circuit circuit (PCB) board at home. There are different ways to apply your design to the copper board, and different etchants to choose from, all with their own pros and cons.

For this tutorial, we are using the Press-n-Peel film that you can get from your local electronics store, including Jaycar (Part no. HG9980) or Altronics (Part no. H0770, pictured).

Note: This toner transfer method will require the use of a photocopier or laser printer to get your design onto the film, as inkjet printers cannot be used.

We will use ferric chloride etchant, available from Altronics (Part no. H0800). This is supplied in a 500ml bottle, premixed for easy use.

In our next issue, we will teach you how to use positive resist coated PCBs and use ammonium persulphate as our etchant.

SAFETY

Ferric chloride, whilst one of the safer etching chemicals, is still a very caustic chemical capable of producing severe burns and is hazardous to animal life. Thus, before we get started, it is imperative that you take a moment to consider the safety aspects of this process. You will be dealing with high heat and very caustic chemicals. As such, we implore you to follow at the very minimum the basic safety precautions outlined here:

• You need to have a clean work area, and free of any flammable materials.

• Read the label on the etching chemical’s container

• Read the material safety datasheet (MSDS) for the chemical you are using!

• Remove any trip hazards in the area where you are using the Ferric Chloride. This includes making sure children and pets are not in the room at the time.

• You MUST wear basic PPE including long sleeves, nitrile gloves, and eye protection.

• Work in a well-ventilated area.

• Cover all work surfaces in a disposable drop sheet, newspaper at a minimum.

• Do not dispose of this material into the garbage or drains. It MUST be stored in a clearly marked bottle and disposed of at a chemical disposal/recycling facility.

• Ferric Chloride will permanently stain nearly any surface (even glass) it comes into contact with, and will start corroding any ferrous metal on contact. You must take practical steps to ensure that the liquid does not make contact with any surfaces you don’t want to be damaged.

The process also uses other chemicals that makers are likely more familiar with such as Isopropyl alcohol and Acetone. If you are not familiar with the safety

precautions for these chemicals you will also need to consult the MSDS from them and follow the directions.

TONER TRANSFER METHOD

The first step in the etching process is transferring your PCB CAD model onto the copper-clad PCB. Our favourite method

is to print the design onto some glossy paper using a toner/laser printer.

Note: This method will not work with an inkjet printer. Toner is essentially a very fine plastic powder that is melted and deposited onto paper. This process takes this plastic and by reheating it while in contact with the copper clad PCB causes it to transfer from the glossy paper onto the copper.

Whilst this can be done with any glossy paper, we like to use the Press-n-Peel PCB film that you can find at most electronics stores. The film is specially formulated and safer for your domestic iron due to having a high temperature tolerance.

To print the PCB design, you need to use the layer settings to turn off the layers that are not needed. For our example (using EAGLE), all we need is the Bottom layer and Pads.

Press CTRL + P to print (Command + P on a Mac). This will bring up the print dialog box. Make sure your printer and paper settings are set correctly, the scale factor is set to 1, and the Solid and Black options are both selected (ticked). ››

IMAGE CREDIT: Altronics


PCBEASY


››To save paper, you can have the board print in the corner rather than the default centre. This allows you to print more designs on one sheet.

Make sure you print on the matte side of the Press-n-Peel paper, so you need to know which way to put it in your printer. There is usually a small icon on the printer tray to show you which side gets printed on. Another trick to work out which side prints on your printer is to write on a piece of A4 paper and feed it through the printer.

ETCHING PROCESS

Once you have familiarised yourself with the Material Safety Data Sheet (MSDS) for Ferric Chloride, identified potential hazards, and implemented practical control measures, you can get started with the etching process.

The first step is to get the necessary equipment ready, including:

• Kettle• Paper towel• Nitrile gloves• Eye protection• Sandpaper / scourer pad• Dishwashing detergent• Ferric Chloride• Isopropyl alcohol• Acetone• Iron• Sticky tape• Sheet of A4 paper• Felt tipped permanent marker• Containers and bowls• Plastic drop sheet or large garbage bag• Lanolin or Vaseline (for hands and forearms followed by gloves)• Plastic tongs or cheap tweezers (to pick up the PCB)

You will need a container of Ferric Chloride and a container of cool water. These must be something you are either happy to keep for

the sole purpose of etching PCBs or something you’re happy to discard. If you intend to keep the container, it is imperative that you clearly mark the container as not suitable for use with foodstuffs. This should prevent someone from using the container at a later date to store food.

Paper towel and lots of it. As we said earlier, Ferric Chloride will stain nearly any surface it comes into contact with and even skin.

Note: Lanolin or even Vaseline should be applied to hands and forearms followed by gloves. Plastic Tomgs or cheap tweezers should be used for picking up the PCB. Paper towel can be placed on the work surface to help reduce the staining in the event of drips or spills, however, it’s also needed to clean the PCB and your hands.

An iron or, in our case, a modified laminator. You need a way to transfer the toner from the glossy paper to the PCB substrate. For this, you can simply use an iron set to about 110°C – 170°C.

Isopropyl Alcohol and Acetone are both needed for the process. The alcohol is used to clean the PCB surface allowing the toner to transfer as best as possible, and the Acetone is used to remove the toner from the etched PCB, preparing it for soldering.

Ferric Chloride works much quicker when the solution is warm. We like to fill a large bowl with warm water at about 50°C and place the Ferric Chloride bowl into it. This allows the Ferric Chloride to heat up and it also adds another level of protection from spills.

To ensure the best possible transfer, the PCB needs to be clean and free from oxidation. You could use a very fine sandpaper, a powder like Ajax, soaped fine steel wool or 3M green scourers, but avoid using heavy grit sandpaper or metal scourers. We wet the blank PCB and add a small drop of dishwashing detergent to the surface. This helps remove any oils from the surface (Copper clad board often ships with a fine machine oil coating to reduce oxidation in transit). We then use the scourer or sandpaper to thoroughly clean the surface until it is shiny.


PCBEASY


Being careful not to touch the now clean copper side of the PCB, you want to secure the Press-n-Peel sheet with the printed / matte side facing the copper of the PCB using a small piece of sticky tape. This will ensure that the design does not move during the transfer process.

Pay very careful attention to the placement of the design on the PCB to ensure that all of the desired detail will be transferred correctly. Once you’re happy with the placement you can then fold a sheet of A4 paper in half and place the PCB with attached transfer sheet inside the sheet of paper. This paper will protect your iron or, in our case, modified laminator if the plastic tape or sheet melts.

TRANSFERRING THE TONER

To transfer the toner, we need to heat the PCB and Toner up to between 110°C – 170°C. This allows the toner to reach its glass transition point and thus, melt sufficiently to stick to the PCB. This can easily be done using a clothes iron. In our case, we have an A4 laminator that has been modified to heat to 160°C.

The idea here is to keep the toner in the glass transition temperature range and have sufficient pressure on the PCB printout sandwich to allow for the transfer to happen. The temperatures, pressure, and time are essentially dependent on the toner your printer is using.

Some printers may use toner that reaches this glass transition temperature at the lower range while others may need a much higher temperature. Too low of a temperature and the toner will not transfer correctly and too hot a temperature and the toner becomes very low viscosity and smudges on the copper, producing poor results.

The best practice is to find the ideal temperature for your printer / toner configuration. Start by setting your iron to the lower / synthetic setting. With the PCB and transfer inside the A4 sheet and placed on a hard and heatproof surface, apply the iron to the PCB / A4 sandwich.

Keep firm pressure on the PCB without any movement for about one minute, then gently move the iron around on the A4 paper for another minute or two.

Remove the iron and wait a few minutes for the PCB to cool enough for you to safely touch the surface. Once cool, carefully peel the Press-n-Peel paper away from the PCB and inspect the transfer.

In the images shown here, the image transfer has failed. You can see large areas where the image simply did not stick to the PCB and other areas where the toner was patchy. This can be caused by either an improperly cleaned PCB or insufficient heat / pressure.

Check the design has transferred completely to the PCB and that all of the traces are clear and complete. If the transfer has significant issues, it’s possible that the iron was not hot enough or the board was not cleaned sufficiently. In this case, use Acetone to clean the toner from the PCB and repeat the process with another printout increasing the temperature a little.

A successful transfer will look similar to this image. The traces are well detailed with fairly sharp edges, with no breaks or smudges. ››


PCBEASY


››The transfer wasn’t perfect though, as we can see here there are a few areas where the transfer missed or was not great. This can be caused by a little dust on the PCB between the PCB and the transfer or some oils remaining on the PCB. In either case, these can be rectified by using a Etch Resist Pen or Staedtler permanent marker to touch up the area. This marker will cover the copper and prevent the etchant from eating into that specific area.

Note: Also look for any excess toner, perhaps in fine areas, and use a model makers scalpel to scratch away unwanted toner, or even to cut a track perhaps to add a fuse or resistor, etc.

Since the issues in our example were only on the ground plane and not on any crucial traces, we simply ignored them and etched the PCB.

ETCHING AWAY THE COPPER

The next step is to remove the copper from the exposed areas of the PCB. This can be done with different chemicals, such as Ferric Chloride and Ammonium Persulphate. In either of these cases, warming the chemical can help speed up the etching process. Each has a best temperature for best etching speed, and most economic use.

Our preferred method to warm the etchant is to use a bain-marie type setup using a large tray to hold the hot water and the smaller tray to hold the etchant. This method evenly distributes the heat, without getting water into the etchant.

In our demonstration, we will use Ferric Chloride, which is used undiluted and has a recommended temperature between 20-50°C according to the instructions.

Note: Ammonium Persulphate is an alternative to Ferric Chloride. It is a cleaner chemical to handle compared to Ferric Chloride, however, it isn’t as effective. This white powder needs to be mixed with water (1:5 ratio) and heated to around 60-70°C. (Review the container’s label and read the MSDS for proper instructions and safety precautions before using).

With your protective gear on, put enough etchant liquid into the smaller tray so the PCB is fully immersed. Gently place this smaller tray into the larger tray and fill the larger tray with hot (not boiling) water. Ideally, we want the Ferric Chloride to reach around 50°C.

Be very careful here, as we don’t want the tray of Ferric Chloride floating in the water and nor do we want water getting into the Ferric Chloride.

You can now carefully place the PCB into the Ferric Chloride solution. With the PCB in the solution, we gently rock the tray of Ferric Chloride to keep the solution moving. Leaving it sitting stationary will not only significantly slow down the process but it can also cause the copper to be etched from the outer edges in which can potentially cause under-keying on the outer tracks. This is when the copper at the bottom of the trace starts to be corroded. It’s best when fresh etchant is moving over the board.

The length of time it will take to etch the PCB is dependent on many factors. The temperature, solution strength, copper thickness, agitation applied, and the age / number of times the Ferric Chloride has been used. Our board took about an hour to etch.

Note: You can refresh Ferric Chloride by adding some Hydrochloric Acid (HCL) -within limits, of course. Ferric Chloride dissolves the copper from the PCB and as such, it becomes less effective the more use it has seen. In our case, the etchant was nearly at the end of its lifecycle and the process took quite a while. With brand new etchant and at the higher temperature a board such as this can etch in as little as 5 minutes.

To tell if the board has been fully etched you can remove it from the Ferric Chloride solution and give it a rinse in some warm water.

As you can see in our example here, the etching is not uniform. The pink areas are more dissolved than the darker gold areas. Ideally, you should see the copper change from a gold colour to pink, so in our case, the etching is in process but clearly needs longer in the solution.

When the copper has been fully etched away your board should look like this.


PCBEASY


Note: This PCB still has the toner / Press-n-Peel film covering the PCB. This film has gone pink during the etching process.

Note: If you’re not going to use the PCB straight away, we recommend leaving the toner / Press-n-Peel film on the surface of the PCB. This will prevent the PCB surface from becoming oxidized, which makes it difficult to solder to.

If you’re going to use the PCB straight away, use some Acetone to clean the toner and Press-n-Peel film off the PCB. You could also protect the circuit board with circuit board lacquer if you have that available.

Now all that is left is to drill the holes and populate the PCB.

DRILLING THE HOLES

It’s now time to drill the holes. Ideally, this will be done in a drill press with a very fine drill bit (about 1mm). Using a drill press will ensure that the drill is 90° perpendicular to the PCB, which will create clean holes, and more importantly, reduce the chances of damaging your drill bits.

If you don’t have a drill press then a rotary tool such as a Dremel is ideal, but in a pinch, any drill can be used. You just need to make sure you keep the PCB as perpendicular to the drill bit as possible.

We find it isn’t necessary to centre-punch the holes as the etching process creates a divot in the PCB where the copper was removed.

Generally, this prevents the drill bit from (walking) on the surface of the PCB.

POPULATE THE PCB

With the holes drilled you can populate the PCB with your electronic components and solder them in, just as you would another PCB. However, you will note that this PCB does not have any silkscreen to identify item placement, and nor does it have soldermask to ensure that only the solderpads are exposed.

To help identify what parts go where we print out the Tplace, Tnames and Tvalues layers on a sheet of A4 and keep this handy when building our home etched PCBs.

The lack of soldermask is a little more difficult to overcome. We recommend a soldering iron with a fine chisel tip and very thin solder of 0.7mm or ideally less. This will help to reduce the chances of creating undesired short circuits when soldering.

If you’re still having problems, consider increasing the clearances in the design rule options we set earlier.

You should now have a completed circuit board. Congratulations! Now all that is required is to apply power to your circuit and use it in your future electronics projects. ■

NEXT MONTH: ETCHING RISTON COATED PCBS WITH AMMONIUM PERSULPHATE

WANT MORE?For the working EAGLE files, or to discuss this edition of PCBEasy, visit:https://diyode.io/036bbgg


PCBEASY

https://diyode.io/036bbgg


In this issue, we build the electronics to run the LED cube array that we soldered together in Part 1.


OCTOLED3PROGRAMMABLE 8 × 8 × 8 BLUE LED CUBE: PART 2

BUILD TIME: 3 HOURS SKILL LEVEL: INTERMEDIATE

In our last issue, we showed you how to solder all 512 LEDs together to form the 8x8x8 LED structure.

In this issue, we will complete the LED cube with the necessary electronics. We will show you how we came up with the electronics design, how it works, and how to attach the cube array that you built in last month’s issue.

Similar to the 4x4x4 LED cube published in Issue 34, the individual parts are available from most electronics retailers, however, you should also be able to find kits for this project in Jaycar stores shortly after this issue hits the streets.

THE BROAD OVERVIEW

Part 2 of our 3 part project is the electronics section to drive the LED cube array that you should have already successfully soldered together in part 1.

The electronics for this project is a combination of D-type flip-flops, decoders, MOSFETs, and a handful of other components, all controlled by an ATmega328P.

To make assembly easy, and compact, we have designed a double-sided PCB, and we show you an easy way to program the ATmega328P using an Arduino Uno as the ISP.

We complete the project with a test pattern, and in part 3, we will show you how to program amazing animations. ››


PROJECT



PROJECT


››HOW IT WORKS

LED cubes work on the phenomenon called the persistence of vision. This is essentially an optical illusion which tricks our mind into seeing rapidly changing patterns as a stationary image. We will use a technique called multiplexing to achieve this.

For this project, we will have eight 8x8 LED arrays stacked on top of each other with the cathodes of each layer connected to a transistor, which will connect the common cathodes on a layer to ground when active. We will then control the anodes of each LED on a layer.

This way, the only LEDs that can be illuminated at any one time are the LEDs that are pulled high and the layer which is pulled low.

To create the 3D image, we need to very rapidly switch all of the required LEDs on first to their desired state. We then activate the transistor to allow the LEDs to illuminate. We then change the LEDs to suit the next layer and activate the transistor for that layer.

Doing this at a rate faster than 30 times per second gives the illusion that the LEDs on each layer are illuminated at the same time, when in reality, only one layer can possibly be active at any given moment.

This technique significantly reduces the number of pins required to control all 512 LEDs in this array.

MICROCONTROLLER

This is an 8x8x8 LED cube, which means it consists of 8 individual arrays of 8 x 8 LEDs, all stacked on top of each other to create a cube of 512 LEDs with 64 LEDs to each layer.

If we were to control this cube in the same way we controlled the 4x4x4 LED cube, which used a single pin per LED and another pin for each layer, we would need 64 I/O pins for the LEDs and another 8 for the layers. This would be a total of 72 I/O pins! We simply can’t fathom a microcontroller that would have that many I/O pins and certainly not one that would be through-hole technology (THT). As such, we first did some research online for existing LED cubes and their methods of pin expansion. In this research, we encountered an awesome tutorial on the website Instructables by user CHR whose work was used as inspiration for our project.

In this research, we learned of a system using flip-flops as a memory latch and a de-multiplexer to switch between the flip-flops. This system allows us to use 8 I/O pins to control which pixels in a row are illuminated, 8 I/O pins to control which layer is illuminated, 3 pins to control which row on a layer are enabled, and a single pin to control the output enable of all of the flip-flops.

This means we need a microcontroller that has a minimum of 20 I/O pins all of which must be controllable as a digital output.

Lucky for us, the humble ATmega328P that we are used to in our Arduino Uno and Nano projects just scrapes by, having exactly 20 useable I/O pins. Thus, we decided that the ATmega328P will be suitable for our project.

The ATmega328P pinout naming is very different from the Arduino naming convention. This pinout diagram shows both the Atmel and Arduino naming nomenclature.

Digital pins 0 - 7 (Port D pins 0 - 7) will be used to control the pixels per row.

Analog pins 0 - 5 (Port C pins 0 - 5) will be used to control layers 1 - 6.

Digital pins 12 - 13 (Port B pins 4 and 5) will be used to control layers 7 and 8.

Digital pin 8 - 10 (Port B pin 0 - 2) will be used to control the decoder.

AREF will have a 0.1µF bypass capacitor to ground as close to the pin as practical. This isn’t absolutely necessary since we will not be using the ADC of the microcontroller, however, it is still good practice.

The crystal pins Port B pin 6 and Port B pin 7 will be connected to a 16MHz crystal oscillator, and must have a 22pF load capacitor to ground on both pins. This ensures that the clock of the microcontroller is as stable as possible.

For transient protection and ripple reduction, VCC of the microcontroller will have a 0.1µF ceramic bypass capacitor and a 100µF electrolytic capacitor as close to the pin as practical. The 0.1µF will give any electrical noise or other such voltage spikes a path to ground, and the large electrolytic will help to reduce any ripple on the 5V line.

Reset will have a 10KΩ pull-up resistor and a tactile push button, which when pressed, will pull the reset pin low causing the Arduino to reboot.

ResetDigital Pin 0 (RX)Digital Pin 1 (TX)Digital Pin 2Digital Pin 3 (PWM)Digital Pin 4VCCGNDCrystalCrystalDigital Pin 5 (PWM)Digital Pin 6 (PWM)Digital Pin 7Digital Pin 8

Arduino Function:

Analog Input 5Analog Input 4Analog Input 3Analog Input 2Analog Input 1Analog Input 0

GNDAnalog Reference

VCCDigital Pin 13Digital Pin 12

Digital Pin 11 (PWM)Digital Pin 10 (PWM)

Digital Pin 9 (PWM)

Arduino Function:

ATm

ega3

28P

PD1PD2PD3PD4VCCGNDPB6PB7PD5PD6PD7PB0

PD0PC6

34567891011121314

21

262524232221201918171615

2728

PC3PC2PC1PC0GNDAREFAVCCPB5PB4PB3PB2PB1

PC4PC5


PROJECT


D TYPE FLIP-FLOP

The role of the D type flip-flops in this project is as a simple memory latch. They hold the desired state on the output, irrespective of changes on the input.

To set their state, we pull the input pins 1D - 8D into a desired state of the output pins 1Q - 8Q. We then pull the clock pin (CLK) from low to high and have output enable (!OE) low.

Note: A high on the input will provide a high on output as there is no inversion.

However, the flip-flop’s will keep this same output no matter what happens on the input pins, until such time as the output enable pin is pulled low and the clock pin transitions from low to high. This can be seen in the truth table below.

INPUTS OUTPUT

OE CLK D Q

L ^ H H

L ^ L L

L H or L X Q0

H X X Z

The output(Q) of these flip-flops is connected to the anode of the LED in that position via a current limiting resistor. Thus, when an output pin is pulled high on the flip-flop, current can flow through the flip-flop into the LED and through the active layer MOSFET to ground.

More importantly, it will remain in this state until the clock pulses undergo a change from low to high, in which case, the output will change to match the input and once again stay in this state.

To cover all of the 64 LEDs required for a layer, we need to use 8 of these flip-flop ICs with each flip-flop IC containing 8 flip- flops, and thus controlling one row of 8 LEDs.

3-8 DECODER

We are using the decoder as a way to control the clock signals for the 8 flip-flops. Each of the 8 outputs of the decoder is connected to the clock (CLK) pin of a flip-flop. We can then use 3 pins from the microcontroller connected to A,

2D3D4D5D6D7D8D

GND

1DOE

345678910

21

1817161514131211

1920

2Q3Q4Q5Q6Q7Q8QCLK

1QVCC

SN74HC574N

CG2AG2B

G1Y7

GND

BA

345678

21

1413121110

9

1516

Y1Y2Y3Y4Y5Y6

Y0VCC

SN74HC138N

B, and C of the decoder to control which of the outputs are high at any given time.

To do this, we first need to consult the truth table for the decoder.

INPUTSOUTPUTS

ENABLE SELECT

G1 !G2A !G2B C B A Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7

X H X X X X H H H H H H H H

X X H X X X H H H H H H H H

L X X X X X H H H H H H H H

H L L L L L L H H H H H H H

H L L L L H H L H H H H H H

H L L L H L H H L H H H H H

H L L L H H H H H L H H H H

H L L H L L H H H H L H H H

H L L H L H H H H H H L H H

H L L H H L H H H H H H L H

H L L H H H H H H H H H H L

As we can see, there are 3 address pins on this decoder G1, !G2A and !G2B. For our operation we need to tie !G2A and !G2B to ground potential and G1 to 5V.

In this configuration, we can create a program loop that will change the state of the address pins (A, B, and C), which will pull one output low as per the truth table.

That is to say, if A, B, and C are all pulled low output Y0 will be low and all other outputs will be high.

If we pulled input A high and B and C low. output Y1 will be low and all other pins high, etc. In this transition, Y0 which was low is now pulled high.

Since the 74HC574 flip-flops are edge triggered i.e. work on the leading edge of a transition of the clock pulse from low to high, this change from Y0 will be detected as a clock pulse by the flip-flop, and thus, the flip-flop will remember the state of its input pins until it is changed again by another clock pulse. ››


PROJECT


››LAYER MOSFETS

In order to control the layers, we opted to use the commonly available IRF540N MOSFET. This MOSFET, whilst overkill for the application, was selected as it is a very commonly available part from our local distributors.

We used a 10KΩ pulldown resistor on the base of each of the MOSFETs to ensure that the gates were not susceptible to noise, and also added a current limiting resistor to protect the microcontroller from damage. The IRF540N has quite a large gate capacitance, and whilst no DC current flows into the gate of a MOSFET, AC current can.

The 220Ω resistor on the gate will ensure that the fast switching speed does not allow too high a current to enter the gate, damaging the microcontroller by exceeding the maximum current output of 40mA.

10K

220R

IRF540

THE CUBE

It’s important that we explain how the cube is constructed so you will understand certain terminology while reading the construction and programming text. As such, we will briefly explain the construction, and show diagrams outlining the cube’s construction and the nomenclature used in this guide.

The cube itself is essentially 8 identical layers stacked on top of each other with every LED on a layer sharing a common cathode (negative). When we refer to a layer, it is as indicated here where layer 0 is the bottom layer and layer 7 the top.

We start at zero because the program uses an array and arrays in C++ start at zero.

Each layer is constructed using 64 LEDs, which we will later break down into 8 rows of 8 LEDs.

Each one of the rows of 8 LEDs are connected to one of the flip-flops, and as such, it’s important to note that when we refer to a row, we are referring to its position on a layer.

The anodes of the LED in one layer are then also connected to the anode of the LED directly above and below to form columns. We will refer to these columns as either columns or pixels. In the construction sense, they are columns as there make up an important part of the structure. Whereas, in the programming sense, we are more likely to refer to them as a pixel on a specific layer.

1

8

7

6

5

4

3

2

1

2

3

4

5

6

7

8

Layers 1 - 8 shown.

Rows 1 - 8 shown.


PROJECT


As with most of our projects, we assemble a prototype of the circuit as you see here. This prototype, whilst only a partial prototype, allowed us to simulate a single layer of the project and was useful in testing the principle of operation. It helped us create and understand the program that we hope will be easy enough for our readers to understand and therefore modify.

Note: There is no need for you to recreate this prototype. It is way too complex, fragile in the breadboard, and takes several hours to make. We simply wanted to highlight that considerable effort has gone into the design of this project, and to share the sheer beauty of it. ››

ABOVE ▲Johann's prototype to determine which Flip-Flop ICs would work best.

RIGHT ►Johann putting the circuit through its paces and testing the performance of the MOSFETS.

The Prototype:


PROJECT


PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 x SN74HC138N Decoder ZC4846 Z8638 -

8 x SN74HC574N D-Type Flip-Flops Element14: 9591630

1 x ATmega328P Microcontroller ZZ8727 Z5126 CE04547

8 x IRF540N MOSFETs ZT2466 Z1537 COM-10213

1 x 16 pin DIP IC Socket PI6502 P0565 PRT-07938

8 x 20 pin DIP IC Sockets PI6504 P0568 -

1 x 28 pin DIP IC Socket PI6510 P0571 CE06469

1 x 16MHz Crystal Included with ZZ8727 V1289A COM-00536

1 x Tactile Pushbutton SP0601 S1120 FIT0179

1 x 2.1mm DC Jack PS0519 P0620 PRT-00119

2 x 22pF Ceramic Capacitors RC5316 R2814 CE05189

11 x 0.1µF Ceramic Capacitors* RC5496 R2865 ADA753

10 x 100µF Electrolytic Capacitors RE6130 R5123 ADA2193

64 x 120Ω 1/4W Resistors* RR0550 R7536 PRT-14493 ^

9 x 10KΩ 1/4W Resistors* RR0596 R7058 PRT-14491

8 x 220Ω 1/4W Resistors* RR0556 R7542 PRT-14490

4 x M3 x 10mm Screws* HP0406 H3130A FIT0281

4 x M3 Nuts* HP0425 H3175 FIT0281

1 x Double Row 3-pin Header HM3250 # - POLOLU-1023

1 x PCB - - -OPTIONAL:

1 x USB to 2.1mm DC Cable (To Power from a 5V Phone Charger) - P6701 ADA2697

4 x 20mm M3 Standoffs* HP0907 H1250 FIT0063

4 x M3 Screws to suit Standoffs* HP0400 H3110A FIT0063

* Quantity shown, may only be sold in packs.^ The 100Ω resistor from Core Electronics should work fine in lieu of the 120Ω.# The 3-pin header from Jaycar needs to be cut down.

The Electronics Build:


PROJECT


››PCB KEY

This key is very useful for troubleshooting. Once you have installed the components it can be near impossible to see the values printed underneath. Thus, it's incredibly difficult to discover a component installed incorrectly. Having a key like this allows you to systematically check the component in a location without needing to remove it.

Note: The PCB shown here is revision D. There may be some slight modifications to the final design which will be available as a kit from Jaycar and the parts list in this article. The parts list is correct however, the values printed on the PCB shown in this article may not be.

Assembling the project isn’t a complex task, however, there are some steps that need to be followed in a specific order. As such, we have opted to show the step-by-step build process, which we took to construct and test the project.

Naturally, the first step was populating the PCB with the necessary components. For this, we generally start with the low-profile components such as the resistors and work our way up to the biggest, which are the electrolytic capacitors. ››

PART IDENTIFIER VALUE QTY DESCRIPTION

Q1 16MHz 1 CRYSTAL

J1 Centre Positive 1 DC POWER JACK

ICSP Programming header 1 PIN HEADER

C1, C7, C8, C11, C12, C15, C16, C19, C20, C21, C23 0.1uF 11 CAPACITOR, European symbol

C2, C5, C6, C9, C10, C13, C14, C17, C18, C22 100uF 10 POLARISED CAPACITOR, European symbol

R65, R67, R69, R71, R73, R75, R77, R79, R81 10K 9 RESISTOR, European symbol

R1 - R64 120R 64 RESISTOR, European symbol

R66, R68, R70, R72, R74, R76, R78, R80 220R 8 RESISTOR, European symbol

C3, C4 22pF 2 CAPACITOR, European symbol

U1 328P 1 Atmel 328P Microcontroller

Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9 IRF540 8 HEXFET Power MOSFET

JP1 SMD Jumper 1 Normally open solder jumper

S1 MOMENTARY-SWITCH-SPST 1 Momentary Switch (Pushbutton) - SPST

U2 SN74HC138N 1 3 line to 8-line decoders demultiplexers

U3 - U10 SN74HC574N 8 OCTAL EDGE-TRIGGERED D-TYPE FLIP-FLOPS

Top side of the PCB. Note that not all of the ICs face the same direction.


PROJECT


328P

22pF

22pF

0.1µF 100µF

SN74HC574N

SN74HC138N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µuF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

0.1µF100µF

0.1µF

10K

10K

10K

10K

10K

10K

10K

10K

10K

PB5(SCK) 19

PB7(XTAL2/TO SC2)10

PB6(XTAL1/TO SC1)9

G ND8

G ND22

VCC7

AREF21

AVCC20

PB4(MISO ) 18PB3(MO SI/O C2) 17PB2(SS/O C1B) 16PB1(O C1A) 15PB0(ICP) 14

PD7(AIN1) 13PD6(AIN0) 12PD5(T1) 11PD4(XCK/T0) 6PD3(INT1) 5PD2(INT0) 4PD1(TXD) 3PD0(RXD) 2

PC5(ADC5/SCL) 28PC4(ADC4/SDA) 27PC3(ADC3) 26PC2(ADC2) 25PC1(ADC1) 24PC0(ADC0) 23PC6(/RESET)1U1

Q1

C4

C3

C1 C2

VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U3

VCC16

G 16

~G 2A4

~G 2B5

A1

B2

C3

G ND8

Y0 15

Y1 14

Y2 13

Y3 12

Y4 11

Y5 10

Y6 9

Y7 7

U2

C7C5VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U5

C11C9VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U7

C15C13VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U9

C19C17

VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U4C8C6

VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U6C12C10

VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U8C16C14

VCC20

~O E1

CLK11

1D2

2D3

3D4

4D5

5D6

6D7

7D8

8D9

G ND10

1Q 19

2Q 18

3Q 17

4Q 16

5Q 15

6Q 14

7Q 13

8Q 12

U10C20C18

C21C22

C23

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

P$1

321

J1

1Row 1

2345678

9Row 2

10111213141516R

65

17Row 3

18192021222324

25Row 4

26272829303132

33Row 5

34353637383940

41Row 6

42434445464748

49Row 7

50515253545556

57Row 8

58596061626364

LAYER_1 LAYER_2

VCC

LAYER 8 CATHODE

LAYER 7 CATHODE

LAYER 6 CATHODE

LAYER 5 CATHODE

LAYER 4 CATHODE

LAYER 3 CATHODE

LAYER 2 CATHODE

LAYER 1 CATHODE

220Ω 220Ω 220Ω 220Ω 220Ω 220Ω 220Ω 220ΩLAYER_3 LAYER_4 LAYER_5 LAYER_6 LAYER_7 LAYER_8

+

+ + + +

+ + + +

+

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

120Ω120Ω120Ω120Ω120Ω120Ω120Ω120Ω

››Given the size of the board, and the fact that all of the resistors were in the same direction, we made a conscious effort to place all of the resistors in the PCB so that the colour bands can be read from left to right. This is a small step but can go a long way in assisting with troubleshooting if something were to go wrong.

Our resistors came in a pack of 8 so we did one pack at a time. Bend all 8 resistors from a pack over your finger.


PROJECT


328P

22pF

22pF

0.1µF 100µF

SN74HC574N

SN74HC138N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µuF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

SN74HC574N

0.1µF100µF

0.1µF100µF

0.1µF

10K

10K

10K

10K

10K

10K

10K

10K

10K

PB5(SCK) 19

PB7(XTAL2/TO SC2)10

PB6(XTAL1/TO SC1)9

G ND8

G ND22

VCC7

AREF21

AVCC20

PB4(MISO ) 18PB3(MO SI/O C2) 17PB2(SS/O C1B) 16PB1(O C1A) 15PB0(ICP) 14

PD7(AIN1) 13PD6(AIN0) 12PD5(T1) 11PD4(XCK/T0) 6PD3(INT1) 5PD2(INT0) 4PD1(TXD) 3PD0(RXD) 2

PC5(ADC5/SCL) 28PC4(ADC4/SDA) 27PC3(ADC3) 26PC2(ADC2) 25PC1(ADC1) 24PC0(ADC0) 23PC6(/RESET)1U1

Q1

C4

C3

C1 C2

VCC20

~O E1

CLK11

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LAYER 7 CATHODE

LAYER 6 CATHODE

LAYER 5 CATHODE

LAYER 4 CATHODE

LAYER 3 CATHODE

LAYER 2 CATHODE

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With all 8 bent, insert them into the PCB one at a time, slightly bending the leads out so that the resistor will not fall out as you’re inserting the other 7 resistors.

With all 8 resistors from a pack inserted into their correct location, solder one lead of each resistor to the PCB. Check the front of the PCB to make sure the resistor is sitting flush against the PCB. ››


PROJECT


››Note: Only soldering one lead means that you can easily reposition the resistor. If you find some of your resistors are not seated correctly, you can simply flip the board back over and use a finger to put slight pressure on the offending resistor while you reflow the solder joint with your soldering iron. This should cause the resistor to sit flush against the PCB, but be careful not to burn yourself as the resistors will get very hot quickly.

Once you’re happy that all of the 8 resistors you just placed are positioned correctly, and in the correct spot, you can solder the remaining lead. After this, you can trim the leads.

Note: When trimming the leads, we recommend the use of good quality side cutters. We like to use a flat side cutter often called flush cuts, which are a pair that allow you to get close to the PCB, however, you don’t want to cut flush to the PCB. Rather, you want to cut the lead at the apex of the solder joint as shown here. After cutting the leads, you still want the nice volcano looking shape like the left-hand lead of this LED. Whilst clearly exaggerated in this image, it’s common to see makers cutting the solder joint like the right side thinking that’s the use for flush cuts. Cutting your leads like this may increase the chances of damaging your PCB.

You can now repeat the same process with the remaining 73 resistors.

Note: Be very careful and ensure that you’re using the correct resistors in the correct locations as changing components when the LED array is attached will be a nightmare.

When you’re done, go back over the PCB to make sure no resistors were missed and that the resistors are in the correct positions and soldered correctly. You can use the component key provided to ensure that the components have been soldered into the correct spots. Having the resistors all in the same direction will be very handy here.

Once satisfied, you can move onto the next size of components. In our case, this is the component Q1, which is a 16MHz crystal. It can be found just above the ATmega328P footprint.

The crystal is not polarity sensitive but can be sensitive to heat. It’s good practice to solder crystals as quickly as practical and letting the package cool completely between solder joints. This will significantly reduce the chances of damage. Many datasheets suggest around a 3-second or less solder time at 350°C to guarantee no damage will occur.

The next component on the top side of the PCB is the reset switch. The good news is these switches have the leads bent in a way that they lock into the PCB and don’t easily fall out. Simply insert the switch into the board and solder it in.

Note: The switch will only go in one way and is not polarity sensitive.

With the switch soldered in, you can now move onto the IC sockets. Whilst these are not exactly mandatory given the fact that you’re not likely to replace them, as doing so after construction would necessitate a complete reconstruction of the cube after all. However, we highly recommend them as it’s possible to solder the IC in the wrong way and this becomes very difficult to rectify. With an IC socket, if you put the IC in incorrectly, you can always take it out and replace it. Whereas, trying to desolder an IC soldered directly to a circuit board can be difficult and damage the PCB’s traces and pads.

To solder the IC sockets, we insert the socket into the PCB so that the notch on the socket matches the notch on the PCB overlay. We then solder 2 leads in place on opposite corners of the socket. This allows us to double-check that the socket has been installed correctly and is flat against the PCB. If it’s not flat, you can follow the same procedure we used on the resistors i.e. reflowing the solder while pressing against the component.


PROJECT


When you’re satisfied that the socket is installed flush and in the correct position / orientation, you can solder the remainder of the pins.

Note: If you solder the IC socket to the PCB in the incorrect orientation its best at this point to leave it as is. Trying to desolder all 20+ pins will greatly increase the chances of damage to the PCB. You just need to make sure the notch on the IC being inserted into the socket matches the silkscreen markings and not the IC socket.

With all of the IC sockets installed, you can move on to the ceramic capacitors. These are not polarity sensitive, and thus, can be inserted into the PCB in either direction. Like the crystal, these monolithic ceramic capacitors can be sensitive to heat, and the manufacturers recommend that the component be subjected to the soldering temperatures for a maximum of 3-seconds. So, like with the crystal, do your best to ensure that you don’t let the soldering iron dwell on the joint for too long, and let the part cool before attempting a touch up or soldering the second leg.

The next step is to solder the electrolytic capacitors. This component is polarity sensitive and both the capacitor and PCB have markings to help identify this polarity. The capacitors themselves have two methods of identifying the devices polarity. The wrapping on the casing has a negative symbol label on it to show the leg on that side is the negative leg.

Another way to identify the polarity of the electrolytic capacitor is by the positive lead, which is always longer than the negative lead. This longer leg goes into our PCB marked with the + symbol.

You’re now on the home stretch for the top side of the PCB construction. It’s just a case of inserting all of the IC’s into the IC

sockets and being sure to check the notch on the IC matches the notch on the PCB.

Next, flip the PCB over to the back side and add the DC jack and the 2-row 3 pin header.

Take a through look over your PCB to make sure there are no components missing and everything is installed correctly before we start to program.

Note: We will install the MOSFETs and LED structure after programming.

PROGRAMMING THE ATMEGA328P

Even though the MOSFETs are not yet installed, we can still verify that the circuit is working and that the microcontroller is able to be programmed (Imagine finishing the cube and finding out that the microcontroller was faulty?!).

To program the microcontroller on this board, we need an in-circuit serial programmer (ICSP) or sometimes shortened to just (ISP). ››

ABOVE ▲Can you find the missing component?


PROJECT


››There are many programmers that can be used for this purpose but we will show the process using an Arduino Uno as an ICSP.

The very first step is to upload the ICSP software to the Arduino Uno that we will be using as the programmer. This is a sketch included in the example section of the Arduino Integrated development environment (IDE).

You can find the Sketch by clicking File > Examples > ArduinoISP > ArduinoISP

Scroll down to line 81 and uncomment that line.

It should now read:

This will tell the Arduino that we intend to wire the Arduino using the digital pins and not the ICSP header.

// #define USE_OLD_STYLE_WIRING

#define USE_OLD_STYLE_WIRING

You can then upload the sketch to the Arduino Uno.

Note: If you’re new to Arduino, we thoroughly recommend that you check out our awesome getting started with Arduino guide from Issue 17 called ‘Setting up the Arduino IDE’. This will show you the process of using the Arduino IDE on various different operating systems.

With the Arduino as ISP programming sketch uploaded to the Arduino Uno, we can start connecting the Uno to the ICSP header on the PCB of the 8x8x8 LED cube.

Note: Disconnect the Arduino Uno from the USB port while making these connections.

With the Arduino Uno as our ISP connected to the 8x8x8 LED cube, we can now upload programs. However, we need to power the LED cube first. To aid in this, we have made it possible to power the LED cube’s electronics directly via the programmer. Simply solder the solder bridge across a jumper (JP1) on the bottom of the PCB.

Note: This should not be done with the LED array attached. You will not be able to power the entire cube from this pin using the Arduino Uno as the programmer, as this will exceed the current capabilities of the Arduino and possibly your computer’s USB port.

ARDUINO UNO LED CUBE5V 5V

GND GNDDigital Pin 13 SCK (Serial Clock)Digital Pin 12 MISO (Master In Slave Out)Digital Pin 11 MOSI (Master Out Slave In)Digital Pin 10 RST (Reset)

GND

MOSI

5V

RST

SLK

MISO


PROJECT


IMPORTANT NOTE: It is very important that after confirming the 8x8x8 LED cube is functioning correctly that you remove this solder bridge and confirm that it is removed. If you power the cube via the DC jack with the Arduino connected to the cube and powered via USB you will be connecting your computer power supply to the cube power supply. If the voltage potential on the supplies is different, a large current could flow from the higher potential supply into the lower potential supply. This could result in damage to any number of components including your computer power supply. Therefore, It is imperative that you remove this solder bridge after this procedure.

If you understandably don’t want to take that risk, you can leave the jumper untouched and power the device via a separate power supply while you run the test program. This way, the 5V supply to the Arduino Uno and the 5V supply to the LED cube are isolated, and current can not flow between them. Since both supplies share a common ground potential, all data signals will still be received fine.

In either case, with the cube powered, you can now upload the provided code to the 8x8x8 LED cube controller.

Open the sketch in your Arduino IDE.

Connect the Arduino Uno to your computer’s USB port and make sure the correct COM port has been selected in the Arduino IDE.

Make sure the programmer is set to Arduino as ISP in the Arduino IDE.

Upload the sketch using the Arduino Uno as an in-circuit serial programmer. Once done, remove the ICSP wires leaving VCC and ground on, if powering via the programmer.

You should now verify that the program was uploaded correctly. We used an oscilloscope but you can also use a multimeter with a little patience.

TESTING WITH AN OSCILLOSCOPE

If like us you’re lucky enough to have your own scope you have a nice easy way to test that the cube is working. We have added some test points on the PCB which will allow you to easily verify that the program is functioning correctly. These test points are attached to the gate of the MOSFETs for layer 6 and 7, and were originally added to help test and compare the performance of two different MOSFETs.

To use them to test if the microcontroller is functioning as expected, you can attach your oscilloscope probes to the test points Gate_Q8, Gate_Q9, and the ground alligator clips to the ground pin.

To aid in this, you may want to solder in some male headers to the bottom of the PCB. This will make it much easier to attach your scope probes.

Set both of your scope’s channels to DC coupling, 2V per division, with a time-base of 4ms per division.

Ensure your scope and probes are both set to x1 as the frequency is well under the 1MHz range. ››


PROJECT


››From here, you should be able to see the voltage at the gate of each MOSFET is a pulsating DC square wave. Both waveforms should have an amplitude close to 5V and the frequency should be around 60Hz.

What you are seeing here is the ‘on’ time for layers 7 and 8. It shows that each layer is only illuminated for around 2ms but is repeated 62 times per second.

In the program, we are triggering an interrupt 500 times a second that writes the values to the flip-flops and then triggers each layer. Thus, we can see that the program is running and can be confident to move on with the rest of the construction.

TESTING WITH A MULTIMETER

If you don’t have an oscilloscope, don’t despair. You can still test that the program has been uploaded correctly with a multimeter, albeit possibly not quite as easy.

If your multimeter has a frequency range, you can use the test points to confirm that you get a frequency of around 60Hz when you place the ground probe on the ground test point and the anode probe on the test point Gate_Q8 or Gate_Q9. This will confirm that the program has been uploaded and is running as expected.

If your multimeter does not have a frequency range, you can still test the program is working by using the voltage range.

The pattern we are drawing in the program is the outline of a cube (You need to imagine it obviously as we don’t have the LEDs connected yet).

If you split the cube into layers, knowing that only one layer is ever on at any one time, we can see that the four corners are the only outputs that will be on for every layer. The inner pixels don’t ever come on and the outer pixels will be illuminated twice out of the 8 layers.

If you were to place the negative probe (black) of your multimeter to ground and the positive (red) to any one of the four corners, you should see a voltage of around 3V. Whereas, if you place it to the outer pins you should see 2/8th of that voltage or 0.75V. This will confirm that the program was uploaded and operating correctly. You can now confidently move on with the rest of the construction.

FINISHING CONSTRUCTION

With the program uploaded and verified, work can begin on the final steps of construction starting with the LED cube array being attached.

ATTACHING THE LED CUBE ARRAY

Before you start, just a reminder to handle the LED cube with care because it can very easily be bent out of shape, which will give it a less than ideal presentation. Dropping the cube, even from a small height, will surely bend it, as would carelessly handling it. On top of that, it requires us to place all 64 LED anodes making up the columns to the PCB. This is a time consuming and stressful process. You need to gingerly manipulate each of the anode columns into their respective hole on the PCB using pliers or tweezers, etc.

To get started, place the LED cube into the 3D printed jig (from Issue 35), which will hold the cube steady and reduce the risk of damaging the cube. Next, ensure that the busbar markings across the PCB align with the busbars on the LED cube. This way, the LED legs forming the columns will be in the correct position. Start at row one, aligning the columns into their respective hole on the PCB so that 1mm or so protruded past the bottom of the PCB.

Solder them to the PCB.

Next, place slight pressure on the PCB so that it is pressed against the remaining 56 LED leads / columns. Using tweezers or long nose


PROJECT


pliers, push the leads which are flush against the PCB into their respective hole. This took us about an hour and a half to complete, requiring constant pressure on the top of the PCB the entire time (You may want to consider a toilet break or have a bite to eat before undertaking this step).

SOLDER THE MOSFETS

Once you have all 64 anodes installed and soldered, the next step is to install the MOSFETs. With the LED cube array soldered on top, it’s impossible to solder the MOSFETs in the usual way (i.e. from the opposite side of the board). To overcome this issue, we made the solder pads for the MOSFET larger than usual on the component side, which will allow you to solder them to the PCB from the same side they are placed.

The tab of the MOSFET aligns with the bar printed on the silkscreen and the first pin aligns with the dot on the silkscreen.

Note: It’s important to cut the legs of the MOSFET before you solder it to the PCB. With the LED cube soldered on top you won’t be able to trim these leads. We just trimmed the leads so that about 3.5mm of lead were remaining from the ridge.

POWER

Power from a 5VDC 1.5A - 2A power supply. We used a USB phone charger with a USB to 2.1mm DC plug cable.

3D PRINTED BASE

The final step is to attach the 3D printed base to the PCB. This base is designed to attach to the PCB via 4 x M3 15mm bolts and nuts. We printed the base on our Cocoon Create i3 at 100-microns layer height, using 3D fillies branded white PLA.

The print is designed to sit flat on the build platform and must be printed with supports due to the overhangs for the PCB brackets.

We printed ours with a raft. In this orientation and settings, it took around 10.5 hours to print. You can speed this up dramatically by reducing the resolution to 200 or 300-microns, which would allow it to print in 5.5hours or 3.5 hours respectively.

If you don’t have a 3D printer you can use brass standoffs in place of the 3D printed case. The standoffs will just need to be 20mm or longer to provide the necessary clearance for the MOSFETs.

TEST PATTERN

Due to time constraints and delays in getting the PCB manufactured, we were unable to provide an example program to display animations on the cube. We were, however, able to create a program that will allow you to display a stationary image on the cube, which we intended to be used as a test program.

However, this test program can quite easily be modified to display any image you choose to program into it.

The program relies on a 2-dimensional array that you can see below: ››

volatile unsigned cube[8][8] = {

{B11111111, B10000001, B10000001, B10000001, B10000001, B10000001, B10000001, B11111111}, //layer 0

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 1

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 2

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 3

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 4

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 5

{B10000001, B00000000, B00000000, B00000000, B00000000, B00000000, B00000000, B10000001}, //layer 6

{B11111111, B10000001, B10000001, B10000001, B10000001, B10000001, B10000001, B11111111}, //layer 7

}


PROJECT


›› As you can see, each layer consists of 8 elements, each 8 bits long. Each one of these elements represents one row of that layer, thus it may be easier to follow if we displayed a layer like this.

This shows the entire first layer (layer 0) in a binary format. It may be even easier to visualise if we were to add it to a table like this.

1 1 1 1 1 1 1 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 1

1 0 0 0 0 0 0 1

1 1 1 1 1 1 1 1

Every ‘1’ indicates that the LED should be illuminated and every ‘0’ means the LED should be off. Hopefully, you’re looking at this code and table, and can easily see how simple it will be to modify the code to display other patterns. The tricky part will, of course, be manipulating the code to produce fluid looking animations.

For now, you can manually modify the code in this two-dimensional array and see what interesting patterns you can make. Be sure to show them off to us on social media though.

Another part of the code you may want to tinker with is the interrupt timer. We created a timer that triggers an interrupt at 500Hz.

{

B11111111,

B10000001,

B10000001,

B10000001,

B10000001,

B10000001,

B10000001,

B11111111

}, //layer 0You may want to have a play with this to help see how the code functions by slowing the interrupt frequency. You can do this by changing the value stored in OCR1A in the line:

Using the equation:

OCR1A = (clock frequency / (prescaler x desired frequency )) -1

The clock frequency is the 16MHz crystal and the prescaler can be 1, 8, 64, 256 or 1024.

Note: the value stored in OCR1A must be lower than 65536 when using timer 1.

So, if you wanted an interrupt frequency of 5 Hertz the OCR1A value should be:

OCR1A = (16000000 / (1 x 5 )) -1 = 3,199,999

This exceeds the maximum of 65536, so we need to change the prescaler. Let’s try again with a prescaler of 64.

OCR1A = (16000000 / (64 x 5 )) -1 = 49,999

This will work and produce an interrupt frequency of around 5Hz.

WHERE TO FROM HERE?

Congratulations on building such a gargantuan project, the soldering alone would be a feat for most people. In the next issue, we will finish off this project by delving into the code and getting some animations displaying. ■

NEXT MONTH: CREATING ANIMATIONS

WANT MORE?For the code, PCB and 3D print files, or to discuss this project, visit:https://diyode.io/036cwbkx

cli();

TCCR1A = 0;

TCCR1B = 0;

TCNT1 = 0;

OCR1A = 31999; // = 16000000 / (1 * 500) - 1

TCCR1B |= (1 << WGM12);

TCCR1B |= (0 << CS12) | (0 << CS11) |

(1 << CS10);

TIMSK1 |= (1 << OCIE1A);

sei();

OCR1A = 31999; // = 16000000 / (1 * 500) - 1


PROJECT

https://diyode.io/036cwbkx


In this month’s What The Tech, we explore and test a Heartbeat sensor module designed for microcontrollers.

Measuring heart rates and related vitals used to be the domain of doctors, nurses and fitness professionals, by connecting up expensive electrocardiograms (EKG) or bulky chest wearables. Nowadays, we can get some vital fitness stats from a smartwatch, fitness wearable, and more recently, from affordable sensors that makers can connect to their favourite microcontroller. ››

FINGER ON FINGER ON THE PULSETHE PULSE

BUILD YOUR OWN BUILD YOUR OWN HEARTBEAT SENSORHEARTBEAT SENSOR

We get hands-on with a heartbeat sensor module to see how effective they are.

► HEARTBEAT SENSOR MODULE (SHOWN ABOVE) XC3740 $9.95 Available now at Jaycar www.jaycar.com.au

Shopping List:



WHAT THE TECH



››THE HEARTBEAT SENSOR

There are many types of heart rate sensors now available to makers, including some from Jaycar, Altroncs and Core Electronics. In this article, we will test the XC3740 Heartbeat Sensor Module for Arduino from Jaycar, which sells for $9.95.

This sensor measures just 20mm x 15mm and communicates with your microcontroller using standard I2C communications. The Jaycar website describes features that include ambient light suppression and low-noise circuitry for optimum performance, with power requirements from 1.8V to 5V with optional 1.8V or 3.3V I2C voltage switching onboard.

It is interesting that this module is described as a heartbeat sensor, rather than what it actually is: a pulse oximetry sensor which can display your pulse rate and the oxygen concentration of your blood.

This diagram is the standard form of Electrocardiogram showing a human’s heartbeat.

This diagram illustrates the standard form for a SpO2 / pulse oximetry reading of a human’s pulse.

P

Q

R

S

TST

SegmentPRSegment

PR Interval

QT Interval

QRS Complex

0

1

2

Whilst it’s true you can detect the heartbeat rate in beats per minute (BPM) using such a sensor, we were pleasantly surprised that this little sensor can do so much more than detect a pulse. This sensor can actually tell you the concentration of oxygen in your blood using a simple but very cool trick with light.

Before the development of pulse oximetry technology in the 1980s, physicians would need to take samples of a patient’s blood, which would be sent to a pathology lab for a test known as arterial blood gas analysis. This process would take significant time and resources and could delay the diagnosis for patients.

This prompted engineers in a Tokyo-based biomedical engineering company to begin researching a portable means to provide near-realtime feedback on a patient’s pulse and oxygen saturation. From this research, the lab designed the pulse oximetry technology widely used in all aspects of healthcare today. This same technology has made its way into consumer electronics such as smartwatches, fitness trackers, and sensors such as these.

HOW IT WORKS

The theory behind this technological feat is actually quite simple. Hemoglobin (Hgb) is a protein in our red blood cells that carries oxygen (O2) to the important areas of our body such as the organs and tissues. It is also responsible for transporting carbon dioxide (CO2) from said organs and tissues to the lungs where it can be expelled from the body via respiration. Oxygenated and Deoxygenated hemoglobin absorbs red and infrared (IR) light differently as shown here.

Thus, by shining a red light with a wavelength between 650nm and 670nm as well as an IR light source with a wavelength between 865nm and 905nm into the human body’s extremities such as fingers, toes or even the ear lobes and measuring the absorbed light with a photodetector, we can calculate the concentration of oxygenated hemoglobin and Deoxyhemoglobin.

Absorption Spectra of Hemoglobin

HgbO2Hgb

Wavelength (nm)

600 650 700 750 800 850 900

RED LED650nm-670nm

IR LED865nm - 905nm

950 1000

Mol

ar e

xtin

ctio

n co

effic

ient

(1/c

m*m

M)

101

100


WHAT THE TECH


During a pulsatile flow of blood, the light will travel through the soft tissues, venous or deoxygenated blood as well as the highly oxygenated arterial blood, whereas, during the non-pulsatile flow there is little to no arterial blood, reducing the amount of light absorbed. We can then calculate the blood oxygen saturation using the formula:

HgbO2 / HgbO2 + Hgb = SpO2

Where:

SPO22 = Blood oxygen saturation

HgbO22 = Concentration of Oxyhemoglobin

Hgb = Concentration of Hemoglobin

The good news for us makers, is that the heartbeat sensor module takes care of all of this for us. The module utilises the MAX30102 IC, which has been designed as a complete all-in-one solution for mobile phones and wearable devices such as fitness trackers. The IC is equipped with ambient light cancellation which helps to reduce spurious readings by adjusting for the levels of ambient light. It also uses a temperature sensor to calibrate itself. Likewise, the LEDs require a precise constant current driver, as any deviation in the supply to the LEDs will result in a change in the brightness, and thus, will create erroneous readings. Therefore, the IC also implements inbuilt LED driver circuits.

The MAX30102 shown here contains both the IR and red LEDs, the photo detector as well as the required driver circuits.

The MAX30102 all in one integrated circuit contains the red and IR LEDs, along with the photosensor and processor. The sensor does all of the heavy lifting, exporting the result via an I²C 2 wire protocol.

For us makers, all we need to do is receive the I²C data from the sensor by using a microcontroller and use an algorithm to process

the raw data into a readable format. Lucky for us, the team over at SparkFun Electronics has already done that for us and has a beautiful Arduino library written for the IC and includes excellent example code.

GETTING IT RUNNING

To get started with the Jaycar sensor, we first download the product datasheet/manual from the Jaycar website. The manual stated that they used the SparkFun MAX3010x library. After a quick search on the SparkFun website, we found a hook-up guide for a similar sensor based on the same IC. This included various sample codes.

At the bottom of the hook-up guide, we found a link to the GitHub page containing the Arduino Library named SparkFun_Bio_Sensor_Hub_Library. You can download the library for this project by following this link: https://github.com/sparkfun/SparkFun_Bio_Sensor_Hub_Library ››


WHAT THE TECH

https://github.com/sparkfun/SparkFun_Bio_Sensor_Hub_Library


Practical Example 1: Serial Output››Our first hands-on test was to confirm that the Jaycar sensor was fully compatible with the Sparkfun library and could display results on the Arduino IDE serial monitor.

Given that the sensor uses the same IC to SparkFun’s, we didn’t expect there to be any compatibility issues, but it’s always better to check first to save you time and effort troubleshooting later if things don’t work.

We were curious to see how the heartbeat plotter worked, so for this test, we chose the ‘4 heartbeat plotter’ example code from the library.

PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 x Arduino Nano or Compatible Board XC4414 Z6372 A000005

1 x Heartbeat Sensor XC3740 - -

* A breadboard and prototyping hardware also required

SENSOR HEADER OPTIONS

The sensor module comes supplied with two different styles of pin headers, providing an option straight and 90° headers depending on your application. For our example. we used the straight headers so we could easily insert the sensor into the breadboard. If you’re wanting to make it portable, we recommend you install the 90° headers as this will allow you to have the joining wires leave the sensor at a more practical angle. Removing the headers can be a bit of a pain too, so choose your option carefully.


WHAT THE TECH


WIRING GUIDE

To replicate our example, all you need is an Arduino Nano or equivalent, the heartbeat sensor, a breadboard and jumper wires. Follow the Fritzing diagram or the following guide to wire up your prototype.

We only need to use the lower set of pins and do not use the top GND, RD, IRD or INT.

THE RESULTS

By uploading SparkFun’s example code to the Arduino Nano and using the serial plotter in the Arduino IDE, we can see a graph of the detected heartbeat.

In our case, the example is only showing the results from the IR sensor and not a combined IR and RED, and thus, it isn’t showing the entire combined pulse oximetry reading.

Usually, a pulse oximeter would use both LEDs to improve the sensitivity. Oxyhemoglobin absorbs infrared light and allows red light to pass through more freely while Deoxyhemoglobin absorbs red light and allows infrared light to pass through more freely. Thus, with this example, we are only seeing the level of absorption of the IR light. As the heart pumps we can see the surge of oxyhemoglobin absorbing more of the IR LED leaving less being reflected back to the photodetector.

This program only uses the IR LED as its only used to count pulses / heartbeats.

Considering that the sensor communicated successfully with our Nano and SparkFun library, we decided to move onto another experiment where we could display results on an LCD display. ››

SENSOR ARDUINO NANOVin 5VSDA A4SCL A5GND GND


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Practical Example 2: Realtime Display using a Nokia 5110››Example 1 was great to show results in a computer screen, but we wanted something that didn’t need to be tethered to the computer. For our second experiment, we chose to use a common and inexpensive Nokia 5110 LCD. This screen can be found at most electronics component retailers aimed at a hobbyist market.

For this example we are using the Nokia_5110 library written by Hossein Baghayi, which you can download here: https://github.com/baghayi/Nokia_5110

PARTS REQUIRED: JAYCAR ALTRONICS CORE ELECTRONICS1 x Arduino Nano or Compatible Board XC4414 Z6372 A000005

1 x Heartbeat Sensor XC3740 - -

1 x 330Ω Resistor* RR0560 R7040 PRT-14490

5 x 4.7kΩ Resistor* RR0588 R7054 COM-10969 **

5 x 10kΩ Resistors* RR0596 R7058 PRT-14491

1 x Nokia 5110 LCD XC4616 Z6348 RTL-10773

* Quantity required, may only be sold in packs. A breadboard and prototyping hardware also required.

This is an awesome basic library that mimics the Arduino serial print functions to write strings to the Nokia 5110 LCD.

Note: In our previous projects using this Nokia LCD, such as the USB soldering iron from issue 16, we used the graphing library from Rinky Dink Electronics. The Rinky Dink library isn’t as simple compared to the library from Hossein, but it is many times more powerful and can enable you to use graphics and graphs. If you’re wanting to develop this project, we recommend you take a look at that Rinky Dink library.


WHAT THE TECH

https://github.com/baghayi/Nokia_5110


The circuit is very similar to our first example, but we are now attaching the Nokia 5110 LCD.

VOTAGE DIVIDER

The Nokia 5110 is controlled via the Phillips PCD8544 LCD controller, which is a 3.3V driver and should be powered by the 3.3V regulator on the Arduino Nano.

However, it should also ideally have a logic level shifter on the logic lines. For this project, we will negate the level shifter and just use some cheap resistors to make a voltage divider.

To do this, we can use the voltage divider formula:

Vout = (Vs x R1) / (R1 + R2)

We want to rearrange the formula to make R1 the subject, so it becomes:

R1 = ((R2 x Vs) / Vout) - R2

Where:

R2 is 10kΩ (pick a high value to reduce current wastage)

Vs = The supply voltage or 5V

Vout = the desired 3.3V

Which becomes:

R1 = ((10k x 5) / 3.3) - 10k == R1 = 5.15KΩ

5.15kΩ isn’t a standard E12 value so we can just pick the closest which is 5.6kΩ. We didn’t have this in our SparkFun resistor kit, but it did have 4.7kΩ that would give an output of 3.4V, which will be fine for this situation.

We chose to use 10kΩ and 4.7kΩ resistors to create our voltage divider/makeshift logic level converter.

InputVoltage

R1

R2 DividedVoltage

WIRING THE CIRCUIT

Wire the sensor and LCD to your Nano:

To connect the LCD pins to the Arduino Nano via a voltage divider, consult this schematic.

With the circuit wired up, it’s now time to upload some code. We used example 5 from the SparkFun library which reads and displays the pulse rate on the serial monitor. We have modified the code that you can find on our website so that it will display the data on the LCD, as well as the serial monitor.

In this configuration the device was capable of reading and displaying the pulse rate on the LCD however, due to the breadboard construction it was very prone to erroneous readings.

TESTING

The sensor is very sensitive to movement, so to avoid erroneous readings, ensure to use the included length of ribbon and spring-loaded toggle to firmly hold your finger or toe securely to the sensor. ››

ArduinoPin

R14.7kΩ

R210kΩ

Nokia 5110 LCDPin

SENSOR ARDUINO NANOVin 5VSDA A4SCL A5GND GND

LCD ARDUINO NANOGND GND

Light 330Ω Resistor (Which connects to ground)

VCC 3.3VCLK Digital pin 3 (via voltage divider)

Din Digital pin 4 (via voltage divider)

DC Digital pin 5 (via voltage divider)

RST Digital pin 6 (via voltage divider)

CS Digital pin 7 (via voltage divider)


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››If you don’t have the sensor properly secured, the readings will be sporadic and nonsensical, which is a very common issue with these sensors and most high impedance sensors.

This diagram shows some common erroneous pulse oximeter readings that you can expect when viewing the SpO2 data in graphical/plotting form.

Normal Signal

Pulse Oximeter Waveform

Low Perfusion

Noise Artifact

Motion Artifact

POWER OBSERVATIONS

We tested the current demands of the circuit and module separately using our Powertech lab bench supply, Uni-T UT804 bench multimeter, and Digitech DMM. The entire circuit, including the Arduino Nano, Nokia 5110 LCD, and the heartbeat monitor consumed 31mA when supplied with 4.96V.

We measured the sensor by itself and found that the module would draw 4.69mA with nothing touching the sensor. When supplied with 5.13V, this changed slightly to 5.81mA when the sensor had a finger on the sensor.

The sensor does not automatically enter any power saving modes and the datasheet does not suggest that any are available. This current demand appears high for a device that you see used as portable wearable devices.

It may be possible to lower the current to the two LEDs, and adjust the sample rate in software, to drop the overall power consumption, however, we have not experimented with this. We also read that it is also possible to software shut down the device to which the device will draw less than 0.7μA. If you’re planning on making a portable wearable device, we recommend you look into these functions to reduce the size of the battery you would require.

All in all, for its $10 price point, this little sensor was enjoyable to experiment with. Whilst it’s clearly not going to replace a specifically designed medical device, it could be very useful for designing your own exercise routine, fitness tracker or even just logging your SpO2 and heartbeat for fun. ■

WANT MORE?For the code, or to discuss this edition of What The Tech, visit:https://diyode.io/036gnyz


WHAT THE TECH

https://diyode.io/036gnyz


http://renew.org.au/what-we-do/energy-consult

http://jaycar.com.au

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