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

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.

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 Made changes: font size, LCD to Driver

Data Acquisition: Vehicle Speed Two part system Hall effect sensor Temperature-stable Stress-resistant Supply voltages of 3 to 24 V Magnet http://media.digikey.com/photos/Allegro%20Microsystems/A1120LUA-T.JPG Made changes

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/A 300 300.8 0.266 504 505.6 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) Single power supply +5V   Advantages Easy installation (current wire intact, has connectors and mounting screws) High immunity to external interference.

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

Current (I) Sensor Problem and Potential Solution 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 ** 2.474 2.47369 16.800 4.2000 4 2.5381 2.43437 4.26 12.650 4.2167 3 2.5255 2.44734 3.19 18.0714 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 Process

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 10.23 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

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 http://ecx.images-amazon.com/images/I/41SsaqCyC3L._SL500_AA300_.jpg

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 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,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 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

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 Zigbee Module for Wireless Data Transfer 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

Cost Description Quantity Cost Cost per Part- # TS-7250 SBC 1 $149.00 USB 802.11g 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

Questions?