1. Wireless Telemetry for Solar Powered Car
School of Electrical and Computer Engineering
Wireless Telemetry for Solar Powered Car
Heather Chang
Farhan Farooqui
William Mann
December 13, 2010

2. Project Overview What is telemetry? Why are we doing this project?
Throughout the solar car race, two escort vehicles accompany the one-man solar-powered vehicle to monitor its safety and performance. The Solar Jackets Telemetry System is an automatic, remote monitoring device that collects and transmits crucial instrumental data from low-power sensors and controllers inside the solar car to its chase car through a radio frequency (RF) transmission.
The Solar Jacket’s telemetry system allows a user to view and store real-time data from the solar powered car. The data will be viewable remotely through a computer program that will be installed on a laptop computer. The main purpose of this system is to provide the individuals in a chase car with real time data that will help monitor performance of the solar car.

3. 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

4. Design Overview
Made changes: font size, LCD to Driver

5. Data Acquisition: Vehicle Speed
Two part system
Hall effect sensor
Temperature-stable
Stress-resistant
Supply voltages of 3 to 24 V
Magnet
Made changes

6. Vehicle Speed Process
Vout switches from 2.8V to V as a south pole comes in close proximity (ca. 25mm) to the sensor
SBC keeps track of ‘LOWS’ to return a RPM measurement

7. Vehicle Speed Test Results
SBC (rpm)
Tachomter (rpm)
Percentage Error (%)
168.1 *
N/A
300
300.8
0.266
504
505.6
0.316
* at no load, the motor was not constant

8. Data Acquisition: Current (I) Sensor
HASS 200-S Sensor:
Nominal current: 200 A
Measurement range: ± 600 A
Low power consumption (5V, 22 mA)
Single power supply +5V
Advantages
Easy installation (current wire intact, has connectors and mounting screws)
High immunity to external
interference.

9. Current (I) Sensor Process
Vout (Analog) = Vref ± (0.625·Ip/Ipn) where Vref = 2.487V Ip = measured current Ipn = 200 (HASS 200 model)

10. Current (I) Sensor Problem and Potential Solution
Change in Vout of current (I) sensor too small
Δi of 10A leads to ΔVout of V
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

11. Current (I) Sensor Potential Solution
Differential Amplifier Circuit

12. 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
1 **
2.474
16.800
4.2000 4
2.5381
4.26
12.650
4.2167 3
2.5255
3.19
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

13. Data Acquisition: AC Voltage
Schematic of AC Voltage divider circuit:

14. DC Voltage
Schematic of DC voltage divider circuit:

15. Voltage Process

16. Voltage Measurement Motor Controller Results
Max voltage Reading on SBC: 96 V
Max Voltage Reading on Oscilloscope: 94 V

17. Voltage Measurement Battery Pack Results
DC Input (V)
SBC measured Voltage (V)
Percentage Error (%)
9.8
10.23
20.321
19.26
5.22
30.857
29.8
3.43
40.358
39.6
1.88
50.252
49.7
1.10
59.988
59.8
0.31
70.729
70.6
0.18

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

19. Temperature Results

20. 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

21. GPS Output
$GPRMC, ,V,,,,,,,101110,,,N*43 $GPRMC, ,V,,,,,,,101110,,,N*42 $GPRMC, ,V,,,,,,,101110,,,N*4C $GPRMC, ,V,,,,,,,101110,,,N*40 $GPRMC, ,V,,,,,,,101110,,,N*47

22. 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.

23. 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

24. SBC Program Routine Constant 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 network
2.75,2.94,2.67,38.33,0.08,0.07,76.2,78.8,0.0,$GPRMC, ,V,,,,,,,081110,,,N*4E

25. 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…

26. Data Storage USB thumb drive attached to SBC Remote laptop storage
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

28. 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.

29. Problems Temperature Sensor Zigbee Module for Wireless Data Transfer
Driver
SPI
Zigbee Module for Wireless Data Transfer
Compatability
Range
Power Consumption

30. Future Work Current Sensor RS-232 Data Reception LCD Range
Power Consumption
Printed Circuit Board

31. Cost Description Quantity Cost Cost per Part- # TS-7250 SBC 1 $149.00
USB g wireless network interface for TS-7250
$35.00
GlobalSat BU-353 Waterproof USB GPS Receiver
$36.95
Hall-effect, uni-polar switch (A1120) switch
$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) **
$8.13
QSOP-24 to DIP-24 Adapter
$12.00
$24.00
Temperature Sensor (MAX1299) **
$7.20
SSOP-16 to DIP-16
$10.00
$20.00
Quad rail-to-rail op amp (LMC6484) 3
$3.61
$10.83
Voltage regulator, 5V, 3A (LD1085V50)
$1.63
Voltage regulator , 3.3V, 1A, input
$1.13
Total Cost
$401.58
** free samples available from MAXIM

32. Questions?