Group 27-SenseWalk

• Mark Applegate (EE)

•Sara Belichki (CpE)

•Matthew Czarniak (CpE)

•Nicholas Heintze (EE)

Motivation & Project Goals

Improve the independence and quality of life for the visually impaired.

Optimize a tool commonly used by the visually impaired.

How to we do this?

Sonar: detect upcoming obstacles and vibrate a motor attached at the user’s wrist.

GPS: the SenseWalk will hold the user’s saved routes to guide them when needed.

Bluetooth: the user will be alerted of upcoming instructions as they go about a route.

Sense Walk System Design

MCU

GPSDigital

Compass

SD Card

Bluetooth

Sonar

Power Supply

Microcontroller

MCU

GPSDigital

Compass

SD Card

Bluetooth

Sonar

Power Supply

Microcontroller Requirements

The SenseWalk requires a microcontroller that contains High flash memory-between 256 KB-512 KB High frequency ADC peripheral Supports UART connection Low power

Microcontroller Options

MSP430F6659 ATmega2560Voltage Supply

1.8 V-3.6 V

Frequency 20 MHz

Flash Memory

512 KB

ADC 16 channels with 12-bit resolution

Supports UART

Yes

IDE CCS/IAR

Price with target board

$149.99

Voltage Supply 5 V

Frequency 16 MHz

Flash Memory 256 KB

ADC 16 channels with 10-bit resolution

Supports UART Yes

IDE Arduino IDE

Price with target board

$58.95

Microcontroller Final Selection

Sonar Design

MCU

GPSDigital

Compass

SD Card

Bluetooth

Sonar

Power Supply

Sonar Specs and Requirements

• Distance From 1 meter to 3 meters• Sonar operate at 40kHz• Not affected by noise • Microcontroller calculate distance• Vibrate a motor at different magnitudes

proportional to distance

Ultrasonic Transducer Selection

  Senscomp 600 Air Ultrasonic 400ST/R

Thickness 0.46” 0.472”Diameter 1.69” 0.63”Frequency 50kHz 40kHzVoltage 200V 20VOperating Temperature

-40 to +85o C -40 to +80o C

Beam Angle 15 o at -6dB 55 o at -6dBCapacitance 400-500pF 2400pFReceiving Sensitivity

-42dB at 50kHz -65dB at 40kHz

Bandwidth Filter Unknown -6dB per 2 kHz

Ultrasonic Drive Circuit Options

555 Timer Square wave is highly distorted by load.

Phase shift Oscillator Square wave is distorted by load.

40kHz Crystal- CMOS Inverter Oscillator Minimum distortion

Ultrasonic Transmitter Circuit

Hex Inverter

Ultrasonic Receiver Circuit

Quad Op Amp

Sonar Testing

Bluetooth

MCU

GPSDigital

Compass

SD Card

Bluetooth Sonar

Power Supply

Bluetooth Requirements

Only needs to be able to cover a short distance (Class 1 BT modules have a range of ~100 m, Class 2 ~10 m).

Needs to have a good data rate to ensure no delay.

Use UART to connected to embedded system.

Low power consumption. Must have appropriate Bluetooth protocol to

send out audio messages to headset.

Bluetooth Comparison

PAN1315 RN-42

Data Rate 2.1 mbps

Distance range

~ 10 m

UART Yes

Voltage Supply

3.3 V

Price $13.71

Data Rate 2.0 mbps

Distance Range

~10 m

UART Yes

Voltage Supply

3.3 V

Price $15.95

Bluetooth Module Selection

RN-42

Navigation Design

MCU

GPSDigital

Compass

SD Card

Bluetooth

Sonar

Power Supply

GPS Module Selection

ls20031

5 Hz update (10 Hz max)

Up to 66 channel input

Cold Start < 35 seconds

Accuracy to 3 meters

Digital Compass Selection

LSM303

I2C serial interface

Operating voltage: 2.5 to 5.5 V

Supply current: 10 mA

SD Card & Breakout Board

San Disk 4 GB Petite FatFS SD Library

Loading Waypoints on SD Card

Use route planner to create CSV / GPX Upload CSV file with waypoints to SD

Software Class DiagramSenseWalk

SDCard Compass GPS Bluetooth

Sonar

SDCardCompassBluetoothSonarGPSInit()getDirection()getCurrentCoordinates()getCurrentWaypoint()sendBluetooth()calculateSonar()determineRelativePos()determineCorrection()

OpenFile()CloseFile()ParseWaypoints()CurrentWaypoint()

calibrateCompass()currentDirection()

establishConnection()currentCoordinates()

ConnectHS()Transmit()

determineDistance()sendMotorCommand()

Power Supply

MCU

GPSDigital

Compass

SD Card

Bluetooth

Sonar

Power Supply

Power Supply Requirements

AC-DC Efficiency Requirements

Energy Star Requirements have become industry standard

“AC-DC External Power Supply- An external AC-DC power supply is an EPS designed to convert line voltage ac input into lower voltage dc output.” [1]

[1] http://www.energystar.gov/ia/partners/prod_development/revisions/downloads/FinalSpecV2.pdf

Output Power: 14.4WMinimum Efficiency Requirement: 73%

Flyback Switching Converter

Magnetic & Capacitive Component Issues

EMI design issuesController & FET selection

• High Efficiency 80+ % capable. • Least costly of all isolated switching power supplies.• Full isolation capable. • Ideal for 0-200Watts. • Limited to 200Watts due to high peak switch currents.

Continuous Conduction Mode VS Discontinuous Conduction Mode

CCM DCM

CCM

Lower ripple current Lower transistor and diode peak

current requirements

Right Half Plane Zero requires complicated control loop

Higher energy in transformer = larger transformer

DCM

Lower energy in transformer = smaller transformer

Less windings = lower I2R Losses

Higher ripple current = output capacitor ESR requirements

Higher transistor and diode peak current requirements

Transformer Design DCM

Primary Inductance: 1.078mH Primary Peak Current: 0.75A Max Input RMS Current: 0.32A Max Output RMS Current: 2.08A Turn Ratio: 8.94

Primary & Secondary Wire Size Core Material Selection Gap Length, Total Winding Area

Transformer Design Equations DCM

Transformer Design Equations DCM

MOSFET Selection

Power MOSFET required - 600V and >2 Amps. Experiment with MOSFETs to find best fit for

efficiency.

Switching losses - Low parasitic capacitances and fast rise/fall times will combat switching losses.

Conduction losses - Low Rds(on) will combat conduction losses.

High Voltage MOSFET Selection

MTP2N60E (ON Semi) NDF03N60ZG (ON Semi) NDF06N62ZG (ON Semi)

VDSS 600V 600V 620V

ID 2A 3A 3.8A

Ciss 435pF 312pF 923pF

Coss 9.2pF 39pF 106pF

tr 21ns 8ns 19ns

tf 24ns 10ns 28ns

RDS(on) 3.3 Ohm 3.3 Ohm 0.98 Ohm

Flyback Converter Schematic

AC-DC Efficiency Vs. Load

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30

10

20

30

40

50

60

70

80

90

NCP1200

NCP1200

Load Current (Amps)

Effi

cie

ncy %

Li-ion Switching Battery Charger

Three states: Preconditioning, Constant Current, Constant Voltage

[2] Courtesy of Texas Instruments

Battery Charger Schematic

Li-ion Battery

Capacity: 2600 mAh Working Voltage: 7.2V

Peak Voltage: 8.4V

Cut off voltage: 5.5 V

Max Charging Current: 2 Amp  Length: 2.8"

Width: 1.45"

Height: 0.8"

Weight: 3.5 Oz

Linear Vs Switching Regulators

Linear

Low Cost Low Design Complexity Low Noise Small size

Poor Efficiency <40% High Heat Dissipation

Switching

High Efficiency 80+% Extended Battery Life

Higher Cost Higher Design

Complexity

Boost converter Schematic

Current Progress

PCB DesignPower Supply

SonarSoftware

BluetoothGPS

Part SelectionDesign

Research

0 20 40 60 80 100

Progress Percentage

Progress Percentage

Who does what?

Power Supply Mark/Nick

Sonar Mark/Nick

Navigation Matt

Bluetooth Sara

Microcontroller Matt/Sara

Current Budget

Item Price

Bluetooth Module $37.97

Bluetooth headset $14.99

Microcontroller + Target Board $58.95

White Cane $27.45

Electronic Components $82.65

Lithium Ion battery $44.90

Sonar transducers $47.54

NCP1200 Demo board (AC-DC) FREE

Vibration motors $7.20

BQ24123 Battery charging demo board FREE

Ls20031 $49.99

SD Card and Breakout Board $19.99

LSM303 $19.99

Miscellanious $129.98

Total $541.60

Project Future Costs $150

Max Budget $1500

Questions?