anson project

www.electronicsengineeringprojects.comAUTOMATED ATTENDANCE SYSTEM

ABSTRACT

‘AUTOMATED ATTENDANCE SYSTEM ’ is designed to collect and manage student’s attendance records from RFID devices installed in a class rooms. Based on the verification of student identification at the entrances system, the RFID tag can be embedded in the ID card of the individual. First to activate a new session(hour) the teacher swipes her RFID tag this marks a new attendance session during which the students can swipe once to increment their attendance. The RFID module operate in 125Khz range, when a tag passes through its vicinity, the module senses its presence and extracts its unique serial number and passes this code into microcontroller which matches the code to the correct person and increments the attendance of the particular person.

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www.engineeringminiprojects.com


CONTENTS

Chapter No TOPIC Page

1. Introduction……………………………….. 04

2. Block Diagram and Description……….… 05

3.Circuit …………………… 09

Circuit Diagram ..........…….……. 10

Circuit Description……………………… 11

4.Software…………….................. 24

5.Printed Circuit Board ……………………….... 30

PCB Layout …………………….…… 43

6.Estimate……………………………………. 44

7.Conclusion ………………………………... 46

8.Bibpiography………………………………… 48

APPENDIX Data Sheets………………….. 50

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INTRODUCTION

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INTRODUCTION

The two major problems faced by organizations are time consuming manual attendance and wastage of electrical power. Our project is going to solve these problems by using RFID technology. The project is designed to store up to 50 card IDs but it is easily scalable up to 65000 card IDs but for that it requires external memory. Radio Frequency Identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. So the RFID is a wireless identification.

Normally the RFID system comprises of two main parts: RFID Reader and RFID Tag. RFID Reader is an integrated or passive network which is used to interrogate information from RFID tag. The RFID Reader may consist of antenna, filters, modulator, demodulator, coupler and a micro processor.

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BLOCK DIAGRAM

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BLOCK DIAGRAM

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LCD

RFID READERMICROCONTROLLER

MAX232

Computer

Power supply


BLOCK CIRCUIT DESCRIPTION

COMPONENTS OF SYSTEM

The figure below shows the basic block diagram of the AUTOMATED ATTENDANCE USING RFID. It contains the following blocks:

1. RFID reader2. RFID tags3. LCD display4. Microcontroller5.MAX2326. Power supply unit

RFID READER

A reader (now more typically referred to as an RFID interrogator) is basically a radio frequency (RF) transmitter and receiver, controlled by a microprocessor or digital signal processor. The reader, using an attached antenna, captures data from tags, then passes the data to the controller for processing. The reader decodes the data encoded in the tags integrated circuit (silicon chip) and the data is passed to the microcontroller for processing

RFID TAGS

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Tags also sometimes are called “transponders”. RFID tags can come in many forms and sizes. Some can be as small as a grain of rice. Data is stored in the IC and transmitted through. The antenna to a reader. The two commonly used RFID Transponders are Active (that do contain an internal battery power source that powers the tags chip) and Passive (that do not have an internal power source, but are externally powered typical from the reader) RFID Transponders.

LCD DISPLAY

The display support 2X16 characters, which means, the LCD can support 2 lines on the display and each line can display up to 16 characters which is relevant as the only essential output to be displayed is the student’s name and ID. Besides LCD Display, the output is displayed on LCD. The diagram of LCD display is shown in Figure and the detailed connections of the LCD is shown in table

MICROCONTROLLER

The microcontroller used is PIC 16F877A. Microcontroller is a general-purpose device, but one that is meeting to read performs limited calculations on data, and contained is its environ based on these calculations. The prime use, of Microcontroller is to control the operation of a machine using a fixed program that is stored in and does not change over the lifetime of the system.

MAX232

The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals.

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http://en.wikipedia.org/wiki/Transistor-transistor_logic

http://en.wikipedia.org/wiki/RS-232

http://en.wikipedia.org/wiki/Integrated_circuit


POWER SUPPLYThese form an important equipment of any Electronics laboratory. Power

supplies are essential for the testing and implementation of any useful electronic

circuit. If power supplies are not available then the only way to provide power

to a circuit is the battery. For long-term use and frequent manipulation these are

not feasible. More over these are not as flexible as modern day power supplies.

They do not provide for overload protection and thermal protection.

CIRCUIT

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CIRCUIT DIAGRAM

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CIRCUIT DIAGRAM DESCRIPTION

The circuit below shows the AUTOMATED ATTENDANCE USING RFID. It contains

1. RFID reader2. RFID tags3. LCD display4. Microcontroller5.MAX2326. Power supply unit

RFID READER

A reader (now more typically referred to as an RFID interrogator) is basically a radio frequency (RF) transmitter and receiver, controlled by a microprocessor or digital signal processor. The reader, using an attached antenna, captures data from tags, then passes the data to the controller for processing. The reader decodes the data encoded in the tags integrated circuit (silicon chip) and the data is passed to the microcontroller for processing.

FEATURES OF RFID READER

a. Low cost solution for reading passive RFID transponder tags.b. Industrial grade casing for better outlook and protection.c. Integrated RFID reader, antenna, LED, power cable and data cable.d. Every reader has been tested before is being shipped.

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e. 9600 baud RS232 serial interface (output only) to PC.f. Fully operation with 5VDC power supply.g. Buzzer as sound indication of activity.h. Bi-colour LED for visual indication of activity.i. Standard RS232 serial cable (female) ready to plug to desktop PC or Laptop.j. 2m reading range.k. 0.1s response time.l. Operating frequency: 125KHz

FIGURE 4.2 PIN DIAGRAM OF RFID READER

RFID TAGS

Tags also sometimes are called “transponders”. RFID tags can come in many forms and sizes. Some can be as small as a grain of rice. Data is stored in the IC and transmitted through. The antenna to a reader. The two commonly used RFID Transponders are Active (that do contain an internal battery power source that powers the tags chip) and Passive (that do not have an internal power source, but are externally powered typical from the reader) RFID Transponders.

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WORKING OF RFID

Information is sent to and read from RFID tags by a reader using radio waves. In passive systems, which are the most common, an RFID reader transmits an energy field that “wakes up” the tag and provides the power for the tag to respond to the reader. Data collected from tags is then passed through communication interfaces (cable or wireless) toPIC16F877A in the same manner that data scanned from bar code labels is captured and passed to computer systems for interpretation, storage, and action.

LCD DISPLAY

The display support 2X16 characters, which means, the LCD can support 2 lines on the display and each line can display up to 16 characters which is relevant as the only essential output to be displayed is the student’s name and ID. Besides LCD Display, the output is displayed on LCD. The diagram of LCD display is shown in Figure and the detailed connections of the LCD is shown in table

DIAGRAM OF LCD DISPLAY

Table Pin connections of LCD Display.

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EEPROM

EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed. In PIC16F877A, the data EEPROM is readable and writable during normal operation (over the full VDD range). This memory is not directly mapped inthe register file space. Instead, it is indirectly addressed through the Special FunctionRegisters.

MICROCONTROLLER

The microcontroller used is PIC 16F877A. Microcontroller is a general-purpose device, but one that is meeting to read performs limited calculations on data, and contained is its environ based on these calculations. The prime use, of Microcontroller is to control the operation of a machine using a fixed program that is stored in and does not change over the lifetime of the system.

The Microcontroller design uses a much more limited set of single and double byte instructions that are used to move code and data from internal memory to the ALU. Many instructions are coupled with pins on the IC package; the pins are “programmable” that is, capability of having several different functions dispending on the wishes of the programmer. The Microcontroller is concerned with getting data from and its own pins; the architecture and instruction set are optimized to handle data in bit and byte size.

Microcontroller will have much type of bit handling instructions. It may have operational code for moving data from external memory to CPU. Microcontroller may have one or two concerned with rapid movement of code and data from external address.

The Microcontroller can function as a compiler with the addition of No external digital parts. Modules vary in data size 4 to 32 bits. For four bit units in huge volume for very simple, and 8 bit units are most versatile.16 and 32 bits are used in high-speed control and signal

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processing applications. Many modules feature a programmable pin that allows external memory to be addressed with the loss of I\O capability.

PIC MICROCONTROLLER

PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, Derived from the PIC 1640 originally developed by General Instrument’s Microelectronics Division. The name PIC initially referred to “Peripheral Interface Controller”. It is available in different configuration via 8 bit, 16 bit,32 bit with instruction set as given below:

Under 8 bit comes- PIC10xxxx,PIC12xxxx,PIC16xxxx,PIC18xxxx,(12 bit instruction set)

Under 16 bit comes-PIC24h,DSPIC30,DSPIC33.(14 bit instruction set)

Under 32 bit comes-PIC32xxxx.(16 bit instruction set)

PICs are popular with developers and hobbyists alike due to their low cost ,wide availability, large user base, extensive collection of application notes, availability Of low cost or free development tools, and serial programming(and reprogramming With flash memory) capability.

Special Microcontroller Features

High performance RISC CPU. Only 35 single word instructions to learn. All single cycle instructions except for program branches which are two-

cycle. Operating speed: DC- 20 MHz clock input DC-200 ns instruction cycle. Up to 8Kx 14 words of FLASH Program Memory, Up to 368x 8 bytes of

Data Memory(RAM). Interrupt capability(up to 12 sources). Eight level deep hardware stack. Direct, Indirect and Relative Addressing modes. Processor read access to program memory.

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Power-on Reset(POR). Power-up Timer(PWRT) and Oscillator Start-up Timer (OST). Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable

operation. Programmable code protection Power saving SLEEP mode Selectable oscillator options In-Circuit Serial Programming (ICSP) via two pins.

Peripheral Features

Timer0:8-bit timer/counter with 8-bit prescaler. Timer1:16-bit timer/counter with prescaler ,can be incremented

during SLEEP via external crystal/clock. Timer2:8-bit timer/ counter with 8bit period register, prescaler and

postscaler. Two Capture ,Compare, PWM modules -Capture is 16-bit, max. resolution is 12.5 ns -Compare is 16-bit , max . resolution is 200 ns -PWM max. resolution is 10-bit. 8-bit, upto 8-channel Analog-to-Digital converter. Synchronous Serial Port(SSP) with SPI (Master mode) and 12C(slave). Universal Synchronous Asynchronous Receiver Transmitter

(USART/SCI). Parallel Slave Port (PSP), 8-bits wide with external RD, WR and CS

controls(40/44-pin only). Brown-out detection circuitry for Brown-out Reset(BOR)

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DEVICE STRUCTURE

Features

Microchip’s PIC micro 8bit MCU’s offer a price/ performance ratio that allows them to be considered for any traditional 8 bit MCU application as well

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as some traditional 4 bit application, dedicated logic replacement and low end DSP applications. These features and price performance mix make PIC micro MCU’s an attractive solution for most applications.

TYPES OF MICROCONTROLLER ARCHITECTURE

There are two types of Microcontroller architecture designed for embedded system

development. These are:

1. RISC-Reduced instruction set computer2. CISC-Complex instruction set computer

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DIFFERENCE BETWEEN CISC AND RISC:

CISC stands for Complex instruction Set Computer. Most PC’s use CPU based on this architecture. For instance Intel and AMD CPU’s are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instructions MCS-51

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family microcontrollers based on CISC architecture. RICS stands for Reduced Instruction Set Computer. The philosophy behind it is that almost no one uses complex assembly language instructions as used by CISC, and people mostly use compilers which never use complex instructions. Therefore fewer, simpler and faster instructions would be better, than the large, complex and slower CISC instructions. However, more instructions are needed to accomplish a task.

MAX232

The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals.

The drivers provide RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does not need to be made more complicated just for driving the RS-232 in this case.

The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V.

The later MAX232A is backwards compatible with the original MAX232 but may operate at higher baud rates and can use smaller external capacitors – 0.1 μF in place of the 1.0 μF capacitors used with the original device. The newer MAX3232 is also backwards compatible, but operates at a broader voltage

range, from 3 to 5.5

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http://en.wikipedia.org/wiki/Farad

http://en.wikipedia.org/wiki/Baud

http://en.wikipedia.org/wiki/Hysteresis


http://en.wikipedia.org/wiki/Power_supply

http://en.wikipedia.org/wiki/Charge_pump


http://en.wikipedia.org/wiki/RS-232

http://en.wikipedia.org/wiki/Integrated_circuit


POWER SUPPLY

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These form an important equipment of any Electronics laboratory.

Power supplies are essential for the testing and implementation of any useful

electronic circuit. If power supplies are not available then the only way to

provide power to a circuit is the battery. For long-term use and frequent

manipulation these are not feasible. More over these are not as flexible as

modern day power supplies. They do not provide for overload protection and

thermal protection.

The following units form the backbone of any modern day power supply

1. Full wave bridge rectifier

2. Filter circuit

3. Voltage regulator

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0 . 1 µF

P O W E R SUP P L Y

U 5LM78M05C /TO

1 3

2

I N O U T

GND

0 . 1 µF

U 3LM78M12C /TO

1 3

2

I N O U T

GND

- +

1

4

3

2

0/12-1.5A

0 . 1 µF

VC C _5V

0 . 1 µF

VC C _12V

4700MF D

4*IN 4001


In the case if modern power supplies, the required power is

derived from the AC mains. For this at first the 230V/50 Hz is step down

using a step down transformer. Then The AC voltage is converted to DC

using a rectifier circuit. The bridge rectifier is considered the apt choice since

it avoids the center-tapped transformer. The ripples from the rectifiers output

are removed by filtering.

The filter can be any of the following:

1. L filter

2. C filter

3. LC filter

4. CRC filter

And we use capacitive filtering.

The function of the voltage regulator is to provide a stable DC voltage for

powering other electronic circuits. The voltage regulator must be capable of

providing substantial output current. They must provide a constant voltage

regardless of changes in load current, temperature, and AC line voltage.

Although voltage regulators can be designed using opamps, it is quicker and

easier to use IC Voltage regulators. Further more, IC voltage regulators are

versatile and relatively inexpensive and are available with features such as

programmable output, current / voltage boosting, internal short –circuit

current limiting, thermal shut down, and floating operation for high voltage

applications.

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SOFTWARE

Software

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char rfid[17],i=0,n=0,attn[10]={0},sel[10]={0};

void main()

{

UART1_Init(9600); //Initializes USART module with baud rate 9600

Lcd_Init(); //Initializes LCD

Delay_ms(1000); //Wait till the modules settles down

Lcd_Cmd(_LCD_CLEAR ); //Clear Screen

Lcd_Cmd(_LCD_CURSOR_OFF); //Switch off cursor from screen

Lcd_Out(1,6,"WELCOME"); //Print welcome at 1st row & 6th column

TRISD0_bit=0;

TRISD1_bit=1;

RD0_bit=0;

if(RD1_bit==0)

{

for(i=0;i<2;i++) //Save the current data to EEPROM

EEPROM_Write(i,0); //Save to 'i'th EEPROM position attendance of 'i'th student

}

for(i=0;i<2;i++)

attn[i]=EEPROM_Read(i); //Read the current attendance of students from EEPROM at power ON time

while(1) //Main infinite loop

{ n=0;

while(1) //UART loop

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{

if(UART1_Data_Ready()) //Check if data is sent by Reader

{

i=UART1_Read(); //Get the data

if(i==13) //If data is stop byte then place terminating character on the string

{

rfid[n]='\0';

break;

}

else if(i==10){} //Remove starting character from the string

else

{

rfid[n]=i; //Add each character received from Reader to the string

n++;

}

}

}

if(!strcmp(rfid,"3F00EDA52B")) //Compare the RFID string

{

Lcd_Cmd(_LCD_CLEAR); //Clear LCD

Lcd_Out(1,2,"Arun :"); //If match found display the name

if(sel[0]==0) //If attendance not incremented

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{

attn[0]++; //Increase attendance of the selected person

sel[0]=1; //Marks current person's attendance as incremented

}

Lcd_Out(1,13,attn[0]); //Display Attendance

UART1_Write_Text("Arun"); //Send the student data to computer

UART1_Write_Text (attn[0]); //Send attendance

}

if(!strcmp(rfid,"3F00ED6845")) //Compare the RFID string

{


Lcd_Out(1,2,"Anson :"); //If match found display the name

if(sel[1]==0) //If attendance not incremented

{

attn[1]++; //Increase attendance of the selected person

sel[0]=1; //Marks current person's attendance as incremented

}

Lcd_Out(1,13,attn[1]); //Display Attendance

UART1_Write_Text("Anson"); //Send the student data to computer

UART1_Write_Text (attn[0]); //Send attendance

}

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if(!strcmp(rfid,"3F00ED7512")) //Check then for teachers RFID tag

{

for(i=0;i<2;i++) //If teacher's tag found then allow students to register again

sel[i]=0; //Starts new session of attendance


Lcd_Out(1,1,"Welcome Sir "); //Displays welcome note

}

for(i=0;i<2;i++) //Save the current data to EEPROM

EEPROM_Write(i,attn[i]); //Save to 'i'th EEPROM postion attendance of 'i'th student

}

}

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Software description

The software is developed in the high level language MikroC.In the beginning, the array to store RFID code is declared. The attendance and selection arrays are declared and initialized to 0.USART module is initialized with baud rate 9600.The LCD is initialized and it waits for a time of 1 second to settle down. Then the screen is cleared and the cursor is switched off.Welcome message is displayed.

For the initialization purpose pin RD0 is made input pin and RD1 is made output pin using TRIS bit.RD0 is set as 0, when RD0 and RD1 is shorted the system resets. If RD1=0, the attendance of ith student is stored at ith position of EEPROM. Read the current attendance of students from EEPROM at power ON time and enters the main infinite loop.

Enters the UART loop and checks whether any data is received. If the received data is stop bit, i.e., 13 terminating character is placed on the RFID string. Else the starting character 10 is detected and removed to accept the 10 bit data and stored in rfid array.

Compare the received string, i.e., the code with code of tag holder, if match is found the name of the individual is displayed. Checks whether attendance is incremented earlier in the same session using selection array. If selection variable for the student is 0 which is initialized so, the attendance in attn array is incremented by 1.And makes the value of selection variable of the student whose attendance is incremented as 1,so that he can use the tag once in the same session. The attendance is displayed in LCD and sent to the computer for storage with corresponding student’s details. In this program this is done for 2 students, whose attendance can be incremented by showing their tags.

In this system it is arranged in such a way that, if the card holder is a teacher his/her unique code will be identified and the selection variable of all students are made 0 by assigning value 0 to sel array. This marks the starting of a new session in which students can increment their attendance once. And displays a welcome message to teacher. The data is sent to save in the EEPROM at ith position, where i is the number of students

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PRINTED CIRCUIT BOARD

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PCB DESIGNING

PCB PREPARATION TECHNIQUES

You need to generate a positive (copper black) UV translucent artwork film.

You will never get a good board without good artwork, so it is important to

get the best possible quality at this stage. The most important thing is to get a

clear sharp image with a very solid opaque black. Nowadays, artwork is

drawn using either a dedicated PCB CAD program or a suitable

drawing/graphics package. It is absolutely essential that your PCB software

prints holes in the middle of pads, which will act as center marks when

drilling. It is virtually impossible to accurately hand-drill boards without

these holes. If you’re looking to buy PCB software at any cost level and want

to do hand-prototyping of boards before production, check that this facility is

available. If you’re using a general-purpose CAD or graphics package, define

pads as either a grouped object containing a black-filled circle with a smaller

concentric white-filled circle on top of it, or as an unfilled circle with a thick

black line (i.e. a black ring). When defining pad and line shapes, the

minimum size recommended for vias (through-linking holes) for reliable

results is 50 mil, assuming 0.8mm drill size; 1 mil = (1/1000)th of an inch.

You can go smaller with smaller drill sizes, but through-linking will be

harder. 65mil round or square pads for normal components and DIL ICs, with

0.8mm hole, will allow a 12.5 mil, down to 10 mil if you really need to.

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Centre-to-centre spacing of 12.5mil tracks should be 25 mil—slightly less

may be possible if your printer can manage it. Take care to preserve the

correct diagonal track-track spacing on mitered corners; grid is 25 mil and

track width 12.5 mil. The artwork must be printed such that the printed side is

in contact with the PCB surface when exposing, to avoid blurred edges. In

practice, this means that if you design the board as seen from the component

side, the bottom (solder side) layer should be printed the ‘correct’ way round,

and the top side of a double-sided board must be printed mirrored.

Media

Artwork quality is very dependent on both the output device and the

media used. It is not necessary to use a transparent artwork medium—as long

as it is reasonably translucent to UV, its fine-less translucent materials may

need a slightly longer exposure time. Line definition, black opaqueness and

toner/ink retention are much more important. Tracing paper has good enough

UV translucency and is nearly as good as drafting film for toner retention. It

stays flatter under laser-printer heat than polyester or acetate film. Get the

thickest you can find as thinner stuff can crickle. It should be rated at least 90

gsm; 120 gsm is even better but harder to find. It is cheap and easily available

from office or art suppliers.

Output devices

Laser printers offer the best all-round solution. These are affordable, fast,

and good-quality. The printer used must have at least 600dpi resolution for all

but the simplest PCBs, as you will usually be working in multiples of 0.06cm (40

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tracks per inch). 600 dpi divides into 40, so you get consistent spacing and line

width. It is very important that the printer produces a good solid black with no

toner pinholes. If you’re planning to buy a printer for PCB use, do some test

prints on tracing paper to check the quality first. If the printer has a density

control, set it to the blackest. Even the best laser printers don’t generally cover

large areas well, but usually this isn’t a problem as long as fine tracks are solid.

When using tracing paper or drafting film, always use manual paper feed and

set the straightest possible paper output path to keep the artwork as flat as

possible and minimize jamming. For small PCBs, you can usually save paper by

cutting the sheet in half. You may need to specify a vertical offset in your PCB

software to make it print on the right part of the page. Some laser printers

have poor dimensional accuracy, which can cause problems for large PCBs. But

as long as any error is linear, it can be compensated by scaling the printout in

software. Print accuracy is likely to be a noticeable problem when it causes

misalignment of the sides on double-sided PCBs—this can usually be avoided

by careful arrangement of the plots on the page to ensure the error is the

same on both layers; for example, choosing whether to mirror horizontally or

vertically when reversing the top-side artwork.

Photo resist PCB laminates Always use good-quality, pre-coated photo resist fiberglass (FR4) board.

Check carefully for scratches in the protective covering and on the surface

after peeling off the covering. You don’t need darkroom or subdued lighting

when handling boards, as long as you avoid direct sunlight, minimize

unnecessary exposure, and develop immediately after UV exposure.

Instagraphic Microtrak board develops really quickly, gives excellent

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resolution, and is available in thin (0.8mm) and heavy copper flavors. On

using spray-on photoresist, you will always get dust settling on the wet resist.

So it is not recommended unless you have access to a very clean area or

drying oven, or you only want to make low-resolution PCBs.

Exposure

The photo resist board needs to be exposed to UV light through the artwork, using a UV exposure box. UV exposure units can easily be made using standard fluorescent lamp ballasts and UV tubes. For small PCBs, two or four 8-watt, 30.5cm tubes will be adequate. For larger (A3) units, four 38cm tubes are ideal. To determine the tube-to-glass spacing, place a sheet of tracing paper on the glass and adjust the distance to get the most even light level over the surface of the paper. Even illumination is a lot easier to obtain with 4-tube units. The UV tubes you need are sold as replacements for UV exposure units, ‘black light’ tubes for disco lighting, etc. These look white, occasionally black/blue when off, and light up with a light purple. Do not use short-wave UV lamps like EPROM eraser tubes and germicidal lamps that have clear glass, because these emit short-wave UV which can cause eye and skin damage. A timer that switches off the UV lamps automatically is essential, and should allow exposure times from 2 to 10 minutes in 15- to 30-second increments. It is useful if the timer has an audible indication when the timing period has completed. A timer from a scrap microwave oven would be ideal. Use glass sheet rather than plastic for the top of the UV unit, as it will flex less and be less prone to scratches. A combined unit, with switchable UV and white tubes, doubles as an exposure unit and a light-box for lining up double- sided artworks. If you do a lot of double-sided PCBs, it may be worth making a double-sided exposure unit, where the PCB can be sandwitched between two light sources to expose both sides simultaneously. To find the required exposure time for a particular UV unit and laminate type, expose a test piece in 30-second increments from 2 to 8 minutes, develop, and use the time which gave the best image. Generally speaking, overexposure is better than underexposure. For a single-sided PCB, place the artwork’s toner side up on the UV box glass, peel off the protective film from the laminate, and place its sensitive side down on top of the artwork.

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The laminate must be pressed firmly down to ensure good contact all over the artwork. To expose double-sided PCBs, print the solder-side artwork as normal and the component side mirrored. Place the two sheets together with the toner sides facing, and carefully line them up, checking all over the board area for correct alignment, using the holes in the pads as a guide. A light box is very handy here, but exposure can also be done with daylight by holding the sheets on the surface of a window. If printing errors have caused slight mis-registration, align the sheets to average the errors across the whole PCB, to avoid breaking pad edges or tracks when drilling. When these are correctly aligned, staple the sheets together on two opposite sides, about 10 mm from the edge of the board, forming a sleeve or envelope. The gap between the board edge and staples is important to stop the paper distorting at the edge. Use the smallest stapler you can find, so that the thickness of the staple is not much more than that of the PCB. Expose each side, covering up the top side with a reasonably light-proof soft cover when exposing the underside. Be very careful when turning the board over, to avoid the laminate slipping inside the artwork and ruining the alignment. After exposure, you can usually see a faint image of the pattern in the photosensitive layer.

DevelopingDo not use sodium hydroxides for developing photo resist laminates. It is

a completely and utterly dreadful stuff for developing PCBs. Apart from its causticity, it is very sensitive to both temperature and concentration, and made-up solution doesn’t last long. When it’s too weak it doesn’t develop at all, and when too strong it strips all the resist off. It is almost impossible to get reliable and consistent results, especially when making PCBs in an environment with large temperature variations. A much better developer is a silicate-based product that comes as a liquid concentrate. You can leave the board in it for several times the normal developing time without noticeable degradation. This also means that it is not temperature critical—no risk of stripping at warmer temperatures. Made-up solution also has a very long shelf-life and lasts until it’s used up. You can make the solution up really strong for very fast developing. The recommended mix is 1 part developer to 9 parts water. You can check for correct development by dipping the board in the ferric chloride very briefly—the exposed copper should turn dull pink almost instantly. If any shiny copper-colored areas remain, rinse and develop for a few more seconds. If the board is under-exposed, you will get a thin layer of resist which isn’t removed by the

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developer. You can remove this by gently wiping with dry paper towel, without damaging the pattern. You can either use a photographic developing tray or a vertical tank for developing.

EtchingFerric chloride etchant is a messy stuff, but easily available and cheaper

than most alternatives. It attacks any metal including stainless steel. So when setting up a PCB etching area, use a plastic or ceramic sink, with plastic fittings and screws wherever possible, and seal any metal screws with silicone. Copper water pipes may get splashed or dripped-on, so sleeve or cover them in plastic; heat-shrink sleeving is great if you’re installing new pipes. Fume extraction is not normally required, although a cover over the tank or tray when not in use is a good idea. You should always use the hex hydrate type of ferric chloride, which should be dissolved in warm water until saturation. Adding a teaspoon of table salt helps to make the etchant clearer for easier inspection. Avoid anhydrous ferric chloride. It creates a lot of heat when dissolved. So always add the powder very slowly to water; do not add water to the powder, and use gloves and safety glasses. The solution made from anhydrous ferric chloride doesn’t etch at all, so you need to add a small amount of hydrochloric acid and leave it for a day or two. Always take extreme care to avoid splashing when dissolving either type of ferric chloride, as it tends to clump together and you often get big chunks coming out of the container and splashing into the solution. It can damage eyes and permanently stain clothing. If you’re making PCBs in a professional environment, where time is money, you should get a heated bubble-etch tank. With fresh hot ferric chloride, a PCB will etch in well under five minutes. Fast etching produces better edge-quality and consistent line widths. If you aren’t using a bubble tank, you need to agitate frequently to ensure even etching. Warm the etchant by putting the etching tray inside a larger tray filled with boiling water.

Tin platingTin-plating a PCB makes it a lot easier to solder, and is pretty much

essential for surface mount boards. Unless you have access to a roller tinning machine, chemical tinning is the only option. Unfortunately, tin-plating chemicals are expensive but the results are usually worth it. If you don’t tin-plate the board, either leave the photo resist coating on (most resists are

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intended to act as soldering fluxes) or spray the board with rework flux to prevent the copper from oxidizing. Room-temperature tin-plating crystals produce a good finish in a few minutes. There are other tinning chemicals available, some of which require mixing with acid or high-temperature use. Ensure that the temperature of the tinning solution is at least 25oC, but not more than 40oC. If required, either put the bottle in a hot water bath or put the tinning tray in a bigger tray filled with hot water to warm it up. Putting a PCB in cold tinning solution will usually prevent tinning, even if the temperature is subsequently raised. For a good tinned finish, strip the photoresist thoroughly. Although you can get special stripping solutions and hand applicators, most resists can be dissolved off more easily and cleanly using methanol (methylated spirit). Hold the rinsed and dried PCB horizontal, and dribble few drops of methanol on the surface, tilting the PCB to allow it to run over the whole surface. Wait for about ten seconds and wipe off with a paper towel dipped in methanol. Rub the copper surface all over with wire wool until it is bright and shiny. Wipe with a paper towel to remove the wire wool fragments and immediately immerse the board in the tinning solution. Don’t touch the copper surface after cleaning, as finger marks will impair plating. The copper should turn silver in colour within about 30 seconds. Leave the board for about five minutes, agitating occasionally; do not use bubble agitation. For double-sided PCBs, prop the PCB at an angle to ensure the solution gets to both sides. Rinse the board thoroughly and rub dry with paper towel to remove any tinning crystal deposits. If the board isn’t going to be soldered for a day or two, coat it with either a rework flux spray or a flux pen.

DrillingIf you have fibreglass (FR4) board, you must use tungsten carbide drill

bits. Fibreglass eats normal high-speed steel (HSS) bits very rapidly, although HSS drills are all right for odd larger sizes (>2 mm). Carbide drill bits are expensive and the thin ones snap very easily. When using carbide drill bits below 1 mm, you must use a good vertical drill stand—you will break drill very quickly without one. Carbide drill bits are available as straight-shank or thick (sometimes called ‘turbo’) shank. In straight shank, the whole bit is the diameter of the hole, and in thick shank, a standard-size (typically about 3.5 mm) shank tapers down to the hole size. The straight-shank drills are usually preferred because they break less easily and are usually cheaper. The longer thin section provides more flexibility. Small drills for PCB use usually come with either a

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set of collets of arious sizes or a 3-jaw chuck. Sometimes the 3-jaw chuck is an optional extra and is worth getting for the time it saves on changing collets. For accuracy, however, 3-jaw chucks aren’t brilliant, and small drill sizes below 1 mm quickly form grooves in the jaws, preventing good grip. Below 1 mm, you should use collets, and buy a few extra of the smallest ones, keeping one collet per drill size, as using a larger drill in a collet will open it out and it no longer grips smaller drills well. You need a good strong light on the board when drilling, to ensure accuracy. A dichroic halogen lamp, under-run at 9V to reduce brightness, can be mounted on a microphone gooseneck for easy positioning. It can be useful to raise the working surface about 15 cm above the normal desk height for more comfortable viewing. Dust extraction is nice, but not essential—an occasional blow does the trick! A foot-pedal control to switch the drill ‘off’ and ‘on’ is very convenient, especially when frequently changing bits. Avoid hole sizes less than 0.8 mm unless you really need them. When making two identical boards, drill them both together to save time. To do this, carefully drill a 0.8mm hole in the pad near each corner of each of the two boards, getting the centre as accurate as possible. For larger boards, drill a hole near the centre of each side as well. Lay the boards on top of each other and insert a 0.8mm track pin in two opposite corners, using the pins as pegs to line the PCBs up. Squeeze or hammer the pins into the boards, and then into the remaining holes. The two PCBs are now ‘nailed’ together accurately and can be drilled together.

CuttingA small guillotine is the easiest way to cut fibreglass laminate. Ordinary

saws (bandsaws, jigsaws, and hacksaws) will be blunted quickly unless these are carbide-tipped, and the dust can cause sink irritation. A carbide tile-saw blade in a jigsaw might be worth a try. It’s also easy to accidentally scratch through the protective film when sawing, causing photoresist scratches and broken tracks on the finished board. A sheet-metal guillotine is also excellent for cutting boards, provided the blade is fairly sharp. To make cut-outs, drill a series of small holes, punch out the blank, and file to size. Alternatively, use a fretsaw or small hacksaw, but be prepared to replace blades often. With practice it’s possible to do corner cutouts with a guillotine but you have to be very careful that you don’t over-cut!

SOLDERING

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Soldering is the joining together of two metals to give physical bonding and

good electrical conductivity. It is used primarily in electrical and electronic

circuitry. Solder is a combination of metals, which are solid at normal room

temperatures and become liquid at between 180 and 200°C. Solder bonds well

to various metals, and extremely well to copper.

Soldering is a necessary skill you need to learn to successfully build

electronics circuits. It is the primary way how electronics components are

connected to circuit boards, wires and sometimes directly to other components.

To solder you need a soldering iron. A modern basic electrical soldering

iron consists of a heating element, a soldering bit (often called the tip), a handle

and a power cord. The heating element can be either a resistance wire wound

around a ceramic tube, or a thick film resistance element printed onto a ceramic

base. The element is then insulated and placed into a metal tube for strength and

protection. This is then thermally insulated from the handle. The heating

element of soldering iron usually reaches temperatures of around 370 to 400°C

(higher than needed to melt the solder). The soldering bit is a specially shaped

piece of copper plated with iron and then usually plated with chrome or iron.

The tip planting makes it very resistant to aggressive solders and fluxes.

The strength or power of a soldering iron is usually expressed in Watts. Irons

generally used in electronics are typically in the range 12 to 25 Watts. Higher

powered iron will not run hotter, but it will have more power available to

quickly replace heat drained from the iron during soldering. Most irons are

available in a variety of voltages, 12V, 24V, 115V, and 230V are the most

popular. Today most laboratories and repair shops use soldering irons, which

operate at 24V (powered by isolation transformer supplied with the soldering

iron or by a separate low voltage outlet). You should always use this low

voltage where possible, as it is much safer. For advanced soldering work (like

very tiny very sensitive electronics components), you will need a soldering iron

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with a temperature control. In this type of soldering irons the temperature may

be usually set between 200 degC and 450 degC. Many temperature-controlled

soldering irons designed for electronics have a power rating of around 40-50W.

They will heat fast and give enough power for operation, but are mechanically

small (because the temperature controller stops them from overheating when

they are not used).

You will occasionally see gas-powered soldering irons which use butane

rather than the mains electrical supply to operate. They have a catalytic element

which, once warmed up, continues to glow hot when gas passes over them. Gas-

powered soldering irons are designed for occasional "on the spot" use for quick

repairs, rather than for mainstream construction or assembly work.

You need to be careful in soldering because most electronic components

are fragile, and heat sensitive. Usually our biggest concern is heat. Low enough

soldering temperature and short enough soldering time keeps components in

good shape. Electronics components are designed so that they can take high

temperatures on their contacts/wires for some time without damage (to

withstand the soldering). Prolonged exposure to high temperature will heat up

when inside of the component can cause damage to it.

Currently, the best commonly available, workable, and safe solder alloy

is 63/37. That is, 63% lead, 37% tin. It is also known as eutectic solder. Its most

desirable characteristic is that its solids ("pasty") state, and its liquid state occur

at the same temperature -- 361 degrees F. The combination of 63% lead and

37% tin melts at the lowest possible temperature. Nowadays there is tendency to

move to use lead free solders, but it will takes years until they will catch on

normal soldering work. Lead free solders are nowadays available, but they are

generally more expensive and/or harder to work on than traditional solders that

have lead in then,

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The metals involved are not the only things to consider in a solder. Flux

is vital to a good solder joint. Flux is an aggressive chemical that removes

oxides and impurities from the parts to be soldered. The chemical reactions at

the point(s) of connection must take place for the metals to fuse. RMA-type flux

(Rosin Mildly Active) is the least corrosive of the readily available materials,

and provides an adequate oxide removal.

In electronics a 60/40 fluxed core solder is used. This consists of 60%

Lead and 40% Tin, with flux cores added through the length of the solder.

There are certain safety measures which you should keep in mind when

soldering. The tin material used in soldering contains dangerous substances like

lead (40-60% of typical soldering tins are lead and lead is poisonous). Also the

various from the soldering flux can be dangerous. While it is true that lead does

not vaporize at the temperatures at which soldering is typically done, particulate

matter is just as dangerous as fumes would be in terms of poisoning and there is

particulate lead present to some extent in the fumes from your flux.

When soldering keep the room well ventilated and use a small fan or

fume trap. A proper fume trap or a fan will keep the most pollution away from

your face. Professional electronics workshops use expensive fume extraction

systems to protect their workers (needed for working safety reasons). Those

fume extraction devices have a special filter, which filters out the dangerous

fumes. If you can connect a duct to the output from the trap to the outside, that

would be great.

Always wash hands prior to smoking, eating, drinking or going to the

bathroom. When you handle soldering tin, your hands will pick up lead, which

needs to be washed out from it before it gets to your body. Do not eat, drink or

smoke whilst working with soldering iron. Do not place cups, glasses or a plate

of food near your working area.

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Wash also the table sometimes. As you solder, at times there will be a bit

of spitting and sputtering. If you look you'll see tiny balls of solder that shoot

out and can be found on your soldering table.

The soldering iron will last longer with proper care. Before and during

use wipe the bit on a damp sponge. Most bench stands incorporate a sponge for

this purpose. When using a new bit, apply solder to it as it heats up. Always

keep a hot iron in a bench stand, or suspended by the hook, when not in use.

Turn of the iron when you do not use it. Periodically remove the bit and clear

away any oxide build up. Regularly check the mains lead for burns or other

damage (change mains lead if necessary).

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PCB LAYOUT

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ESTIMATE

COST ESTIMATION

Item No Price

RFID READER 1 Rs.2000

RFID TAG 3 Rs.225

PIC 16F877A 1 Rs.220

MAX 232 1 Rs.30

DIODES 4 Rs.1.60

CAPACITORS 8 Rs.0.80

LCD 1 Rs.250

RESISTORS 2 Rs.2

PCB 1 Rs.180

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TRANSFORMER 1 Rs.110

CRYSTAL OSCILLATOR 1 Rs.5.50

IC BASES 2 Rs.40

WIRE 1 Rs.35

9 PIN D CONNECTOR 1 Rs.20

TOTAL Rs.3090.20

CONCLUSION

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CONCLUSION

This project is based on microcontrollers. As this is based on AT89S51

which is a commonly used microcontroller, the control and programming is

quite easy. This is just a humble effort to produce a prototype for a device

which helps in keeping an exact record of student attendance using RFIDs

module. Using this device, we can easily detect the difference in power

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withdrawal of RFID tags and it is user friendly. This system can be easily

installed any location where a 220 v power supply is available.

Our project has been a humble effort to produce a prototype for a device

which helps in keeping an exact record of student attendance using RFIDs

module , and we believe our device will find use in various day to day fields.

BIBLIOGRAPHY

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BIBLIOGRAPHY

www.efymag.com

www.alldatasheets.com

Electronics For You Magazine

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APPENDIX

Data sheet of RFID

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DATA SHEET OF PIC

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anson project

Documents

rfid system

rfid devices

rfid module

rfid tags

rfid interrogator

rfid technology

new attendance session

students attendance