Transcript Wireless Telemetry for Solar Powered Car Heather Chang Farhan Farooqui

School of Electrical and
Computer Engineering
Wireless Telemetry for Solar
Powered Car
Heather Chang
Farhan Farooqui
William Mann
December 13, 2010
Project Overview
Wireless
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)
168.1
300
504
Tachomter
(rpm)
161.8-170 *
300.8
505.6
Percentage Error
(%)
N/A
0.266
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
Sensor
Current (I) Sensor Process
Current
measured
and
converted to
volatge
Analog to
Digital
Converter
Voltage
converted
to 12 bit
binary
values
Single
Board
Computer
Binary Values
converted back to
Voltage, Voltage
converted to Current
Measured
Current
Value
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
• 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”
Vout
Percentage
Current (A)
Measured Number Parallel measured with
Vout
Error (%)
with Loops Current (A) * of Loops Resistors Multimeter (V) theoretical
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
Divider
Circuit
Voltage Process
Measured
Voltage
scaled down
Analog to
Digital
Converter
Voltage
converted
to 12 bit
binary
values
Single
Board
Computer
Binary Values
converted and
scaled back to
measured Voltage
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)
10.9173
20.321
30.857
40.358
50.252
59.988
70.729
SBC measured
Voltage (V)
9.8
19.26
29.8
39.6
49.7
59.8
70.6
Percentage Error (%)
10.23
5.22
3.43
1.88
1.10
0.31
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
$GPRMC,201744.394,V,,,,,,,101110,,,N*47
Single-Board Computer (SBC)
• Running Linux at 200 Mhz
– Programmed using C
– Allows for multi-process
scheduling
– Full socket connection
available via network.
• Start-up script to load
drivers for hardware
when powered on.
Asus Wireless-G USB Module
• Easier to interface with SBC
than previous ZigBee module.
• Allows full network
connection
– Built in encryption/checksum
– Socket programming
– Remote debugging (Telnet/FTP)
• Outdoor range up to 1085 ft
• Compatible with standard
Wi-Fi equipment
SBC Program Routine
Constant loop
• Receive data from ADC via SPI bus.
– Convert voltages received to appropriate
measurements
•
•
•
•
Receive data from temperature sensor via SPI bus
Receive new string from GPS receiver
Monitor RPM sensor over 5 second period
Create string containing all new data
– Broadcast string via datagram socket over network
2.75,2.94,2.67,38.33,0.08,0.07,76.2,78.8,0.0,$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
– 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
Cost
Description
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
** free samples available from MAXIM
$401.58
Questions?