Wireless Telemetry System for Solar Vehicle School of Electrical and Computer Engineering Wireless Telemetry System for Solar Vehicle Scott Cowan Elliot Hernandez Tung Le April 25, 2011

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. Source: http://www.ece.gatech.edu/academic/courses/ece4007/10fall/ECE4007L01/ws1/files/sjt_final_presentation.ppt

Design Overview Solar Car Chase Car SBC Current Speed Temperature Laptop Solar Car SBC USB Current Speed Temperature Voltage RS-485/RS-232 GPS Battery Mgmt. Motor Ctrl. MPPT HMI Data Storage SPI DIO Transmitter Made changes: font size, LCD to Driver

Design Problems & Solutions Problem: Programming C code for TCP/IP protocol for file sync Solution: Switched to C++ to use FTP protocol Problem: Using hardware SPI for the ADC converter Solution: Bit-bang(software based) using the SPI bus

Hardware Problems & Solutions Problem: PCB errors discovered too late to correct Solution: Used wires to bypass incorrect traces; corrected schematics and PCB files for future reference

Outside View of Telemetry Box Comm. Jacks Input Terminals USB Ports

Inside View of Telemetry Box Flash Drive PCB SBC USB Hub

Sensor Testing Methods

Voltage Inputs Telemetry box accepts 0-5 Vdc signals Signal conditioner used to convert high voltage signals to low voltage signals at point of origin Three of six voltage inputs scaled for 0-120 Vdc Remaining voltage inputs scaled for 0-5 Vdc

Testing High Voltage Input Available power supply limited to 50 V Inputted 0-50 Vdc into signal conditioner in 5 V increments Compared readings from SBC to Fluke 199C Scopemeter

Testing Low Voltage Inputs Input 0-5 Vdc into telemetry box in 0.5 V increments Compared readings from SBC to Fluke 199C Scopemeter

Voltage Measurement Results DC Input (V) SBC measured Voltage (V) Percentage Error (%) 0.35 N/A 5 4.31 13.80 10 9.44 5.60 15 14.51 3.27 20 19.6 2.00 25 24.7 1.20 30 29.8 0.67 35 34.93 0.20 40 40.06 0.15 45 45.13 0.29 50 50.26 0.52 Percentage error decreases as DC input increases

Current Inputs Telemetry box accepts 10 current inputs with a range of ±140 A To simulate high currents, 10 loops of wire were passed through current sensor

Testing Current Inputs Looped wire connected in series with 12 V battery and 1 Ω, 225 W variable resistor Resistance varied to give various currents Reversed wiring to give negative values Current measured using Fluke 199C Scopemeter with 80i-110s clamp-on ammeter Ammeter readings multiplied by 10 and compared to SBC readings

Current (I) Sensor Results “Simulated” Current (A) with Loops Measured Current (A) Percentage Error(%) 111 109.32 1.51 140 138.7 0.93 57 56.5 0.88 -57 -55.91 1.91 -114 -112.95 0.92 Current sensor is capable of bi-directionality

Temperature Inputs Readings from temperature are incorrect Error occurred after soldering to PCB Cause of error remains unknown

GPS Output $GPRMC,201740.394,V,,,,,,,101110,,,N*43 $GPRMC,201741.394,V,,,,,,,101110,,,N*42 Note: GPS is in the NMEA 0183 format, where the output is $GPAAM,A,A,CR,N,WPTNME*32 The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one "talker" to multiple "listeners" at a time.

Future Testing RS-485 To RS-232 converter Speed sensor input comparison to tachometer

Remote Laptop Program C++ program that runs FTP protocol Can be used on any OS Updates the file from the SBC to host computer every 10 seconds Re-establish the connection when WIFI signal is broken CSV file readable using text editor, Excel, Matlab, etc…

Project Costs

Future Improvements Add LED status sensors to enclosing Upgrade SBC to newer hardware Increase in computation lower power usage Reduce compatibility issues Use hardware interrupts for RPM calculations Correct discovered errors in PCB

Questions?