Wireless Telemetry System for Solar Vehicle

Scott CowanElliot Hernandez

Tung Le

April 25, 2011

School of Electrical and Computer Engineering

Project OverviewWireless Data from the Solar Car to the Chase Car

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

Design Overview

Chase Car

Laptop

Solar Car

SBC

USB

Current

Speed

Temperature

Voltage

RS-485/RS-232

GPS

Battery Mgmt.Motor Ctrl.

MPPTHMI

Data Storage

USB

USB

SPIDIO

Transmitter

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 & SolutionsProblem: PCB errors discovered too late to correctSolution: Used wires to bypass incorrect traces; corrected

schematics and PCB files for future reference

Outside View of Telemetry Box

Comm. JacksInput Terminals USB Ports

Inside View of Telemetry Box

USB Hub

Flash Drive

SBC

PCB

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 0.35 N/A5 4.31 13.80

10 9.44 5.6015 14.51 3.2720 19.6 2.0025 24.7 1.2030 29.8 0.6735 34.93 0.2040 40.06 0.1545 45.13 0.2950 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

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

Inherited Components $322.95Purchases this Semester $204.51

Cost to Replicate $527.46

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?