Wireless Telemetry for Solar Powered Car

Wireless Telemetry for Solar Powered Car

Heather ChangFarhan Farooqui

William Mann

December 13, 2010

Heather ChangFarhan Farooqui

William Mann

December 13, 2010

Project OverviewWireless

Data from the Solar Car to the Chase Car

Objectives• Real-time processing of vital information:

– Measure vehicle speed– Measure battery pack voltage and current– Measure motor controller voltages and currents– Measure outdoor and cabin ambient temperature– Receive vehicle location (GPS)– Receive motor controller status (on/off)– Receive currents, voltages, temperature readings from

solar panels• Wireless link with solar car (at least 100 ft)• GUI displaying data on LCD to driver and on laptop in

chase car• Storage of data in solar car

Design Overview

Data Acquisition: Vehicle Speed

• Two part system– Hall effect sensor

• Temperature-stable• Stress-resistant• Supply voltages of 3 to 24 V

– Magnet

Vehicle Speed Process

• Vout switches from 2.8V to -0.022V as a south pole comes in close proximity (ca. 25mm) to the sensor

• SBC keeps track of ‘LOWS’ to return a RPM measurement

Vehicle Speed Test Results

SBC (rpm)

Tachomter (rpm)

Percentage Error (%)

168.1 161.8-170 * N/A300 300.8 0.266504 505.6 0.316

* at no load, the motor was not constant

Data Acquisition: Current (I) Sensor

HASS 200-S Sensor: • Nominal current: 200 A• Measurement range: ± 600 A • Low power consumption

(5V, 22 mA)

Current (I) Sensor Process Current Sensor

Analog to Digital

Converter

Single Board

Computer

Measured Current Value

Current measured

and converted to

volatge

Voltage converted to 12 bit binary values

Binary Values converted back to Voltage, Voltage

converted to Current

Vout (Analog) = Vref ± (0.625·Ip/Ipn)where Vref = 2.487VIp = measured currentIpn = 200 (HASS 200 model)

Current (I) Sensor Problem and Potential Solution

• Problem – Change in Vout of current (I) sensor too small

• Δi of 10A leads to ΔVout of 0.03125V• ADC can’t recognize change

• Potential Solutions– Amplify signal (differential amplifier)– LEM HASS-50 (measuring range ± 150)

• Δi of 10A leads to ΔVout of 0.125V

Current (I) Sensor Potential Solution

• Differential Amplifier Circuit

Current (I) Sensor Results

“Simulated” Current (A) with Loops

Measured Current (A) *

Number of Loops

Parallel Resistors

Vout measured with Multimeter (V)

Vout theoretical

Percentage Error (%)

with

4.233 4.2333 1 3ohm 2.4998 2.5001 0.01

-4.217 -4.2167 1 ** 3ohm 2.474 2.47369 0.01

16.800 4.2000 4 3ohm 2.5381 2.43437 4.26

12.650 4.2167 3 3ohm 2.5255 2.44734 3.19

18.0714 18.0714 1 1, 2 ohms 2.541 2.4304 4.55* the DC ammeter has a max current of 10A; otherwise, calculated (Vbatt/Rtotal)** reversed the direction of the current sensor*** resistors have a power rating of 200W

Data Acquisition: AC Voltage

Schematic of AC Voltage divider circuit:

DC Voltage

Schematic of DC voltage divider circuit:

Voltage ProcessVoltage Divider Circuit

Analog to Digital

Converter

Single Board

Computer

Measured Voltage

Measured Voltage

scaled down

Voltage converted to 12 bit binary values

Binary Values converted and scaled back to

measured Voltage

Voltage Measurement Motor Controller Results

• Max voltage Reading on SBC: 96 V

• Max Voltage Reading on Oscilloscope: 94 V

Voltage Measurement Battery Pack Results

DC Input (V)SBC measured

Voltage (V) Percentage Error (%)10.9173 9.8 10.2320.321 19.26 5.2230.857 29.8 3.4340.358 39.6 1.8850.252 49.7 1.1059.988 59.8 0.3170.729 70.6 0.18

Data Acquisition: Temperature

• Temperature sensor outputs a binary value• SBC sees binary value as an integer• Divide integer value by 8 to get Kelvin scale• Convert Kelvin scale to Fahrenheit scale

Temperature Results

Data Acquisition: GPS

• GPS Tracking– Plugs into the SBC’s USB

port– Outputs longitude,

latitude and altitude data as ASCII text

– Data captured by the SBC and forwarded to a laptop

– Has a 5 ft long wire

GPS Output

• $GPRMC,201740.394,V,,,,,,,101110,,,N*43$GPRMC,201741.394,V,,,,,,,101110,,,N*42$GPRMC,201742.407,V,,,,,,,101110,,,N*4C$GPRMC,201743.394,V,,,,,,,101110,,,N*40$GPRMC,201744.394,V,,,,,,,101110,,,N*47

Single-Board Computer (SBC)• Running Linux at 200 Mhz

– Programmed using C– Allows for multi-process

scheduling– Full socket connection

available via network.

• Start-up script to load drivers for hardware when powered on.

Asus Wireless-G USB Module• Easier to interface with SBC

than previous ZigBee module.• Allows full network

connection– Built in encryption/checksum– Socket programming– Remote debugging

(Telnet/FTP)• Outdoor range up to 1085 ft• Compatible with standard Wi-Fi equipment

SBC Program RoutineConstant loop• Receive data from ADC via SPI bus.

– Convert voltages received to appropriate measurements

• Receive data from temperature sensor via SPI bus

• Receive new string from GPS receiver• Monitor RPM sensor over 5 second period• Create string containing all new data

– Broadcast string via datagram socket over network2.75,2.94,2.67,38.33,0.08,0.07,76.2,78.8,0.0,$GPRMC,183411.675,V,,,,,,,081110,,,N*4E2.75,2.94,2.67,38.33,0.08,0.07,76.2,78.8,0.0,$GPRMC,183411.675,V,,,,,,,081110,,,N*4E

Remote Laptop Program• Runs on Linux• Listen for any packets being sent through socket

on specified port• Format and display received strings in console• Save received string to CSV file on laptop

– CSV file readable using text editor, Excel, Matlab, etc…

Data Storage

• USB thumb drive attached to SBC– Saves to FAT16 formatted drive– Saves every string broadcasted out in CSV file– 200 byte strings saved every second– ~700kB/hour

• Remote laptop storage– Listening program on remote laptop saves every

string received

Code: Suggestions For Improvement

• Increased compatibility: Listener program could be easily ported to Windows API’s.

• Enhanced GUI or addition of threshold warnings for some measurements could be added to listener program.

• Multiple listeners: Additional addresses could be added to broadcast to more than one laptop.

Problems

• Temperature Sensor– Driver– SPI

• Zigbee Module for Wireless Data Transfer– Compatability– Range– Power Consumption

Future Work

• Current Sensor• RS-232 Data Reception• LCD• Range• Power Consumption• Printed Circuit Board

CostDescription Quantity Cost Cost per Part- #

TS-7250 SBC 1 $149.00 $149.00

USB 802.11g wireless network interface for TS-7250 1 $35.00 $35.00

GlobalSat BU-353 Waterproof USB GPS Receiver 1 $36.95 $36.95

Hall-effect, uni-polar switch (A1120) switch 1 $1.37 $1.37

Magnet Alnico 5 (AlNiCo) 2 $1.17 $2.34

Current Sensor (HASS 200) 4 $26.00 $104.00

12-bit, 16 input channel ADC (MAX11633) ** 1 $8.13 $8.13

QSOP-24 to DIP-24 Adapter 2 $12.00 $24.00

Temperature Sensor (MAX1299) ** 1 $7.20 $7.20

SSOP-16 to DIP-16 2 $10.00 $20.00

Quad rail-to-rail op amp (LMC6484) 3 $3.61 $10.83

Voltage regulator, 5V, 3A (LD1085V50) 1 $1.63 $1.63

Voltage regulator , 3.3V, 1A, input 1 $1.13 $1.13

Total Cost $401.58

** free samples available from MAXIM

Questions?Questions?