Transcript presentation

Vehicle Detector for
Cyclists
Nathaniel Liu
Parth Narielwala
Ian Simon
Introduction
• Radar detects vehicles up to 30m
• Camera provides mirrored rearview on LCD
– Alerts user when radar detects
Purpose/Motivation
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• To help deaf and hear-impaired cyclists
• Promote safer riding
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1: http://www.usdeafcycling.org/
2: http://faculty.stedwards.edu/lbradle3/cycling.jpg
Block Diagram
FMCW Radar
• FMCW: FrequencyModulated ContinuousWave
– Signal constantly changes
in frequency around fixed
reference
• Change is usually linear
– Used to detect stationary
objects
• Unlike Dopplar Radar
Red: transmitted signal
Green: received signal
Radar Block Diagram
Signal Power Transfer
Sawtooth Wave Generator
• Beagle Board couldn’t create a sawtooth wave
– Needed to build with analog components
• Analog
* Figure from http://www.piclist.com/images/www/hobby_elec/e_ckt17.htm
Sawtooth Wave Generator
Sawtooth Wave Generator
VCO:
1.7V  4.11024GHz
3.2V  4.28976GHz
Microstrip Design
• VCO
– Wilkinson Power Divider
– Microstrip Impedance
• High Frequency Amplifier
– Microstrip Impedance
Microstrip Design
Microstrip Design
* From Microwave Engineering, By: David M. Pozar
Microstrip Design
Microstrip Design: VCO
Microstrip Design: Amplifier
http://www.avagotech.com/docs/AV02-0608EN
Microstrip Design: Amplifier
VCO: Voltage-Controlled Oscillator
Post-Mixer Signal Output
No reflective metal:
Post-Mixer Signal Output
Reflective Surface ~1m:
Problems with Finding Δf
• Mismatched impedances
– Reflection dominates return signal
• Resonant frequencies from sawtooth
– Reasoning for 230 Hz differences
Signal Detector
• BeagleBoard couldn’t do Digital Signal
Processing
• Created circuit to detect incoming signals of a
certain level by thresholding
• Alerts BeagleBoard via GPIO
Signal Detector
GPIO
• Input voltage – 1.8V “high” 0V “low”
• First reads samples signal
• Second called by code
– High is default
MicroController
• BeagleBoard-Xm (BeagleBoard.org)
• Archlinux OS (archlinux.org)
• Features essential to project:
– S-video(TV out)
– RS232 Serial Port
– Ethernet Port
– USB Ports
– GPIO Ports
http://farm5.static.flickr.com/4050/4628072223_fa65b3b924.jpg
BeagleBoard Functions
• This microcontroller needs to take in an image from a webcam, flip
it, and then display that on a 3.5” LCD module
• Upon a received signal from the FMCW sensor, the microcontroller
needs to output a caution image in the upper left hand corner of the
display, overlaying the video feed.
• The display must also show the battery level(Either full, half charge,
or low battery)
http://www.carelectronicsworld.com/images/products/detail/AccelevisionLCD35LV01.jpg
http://www.batteriesinaflash.com/blog/wp-content/uploads/2010/08/battery-capacity.jpg
http://www.sealantssupply.com/images/caution-sign.jpg
Rearview Camera
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1
Difficulties/Bugs
• Could not find a proper linux-based operating system
that would work on the BeagleBoard.
– Came across issues with obtaining proper boot files
• Displaying a the desktop GUI on the LCD module
through the s-video was not working
– Had to do with xorg.conf files in the system files of archlinux
• All problems were solved
3
1 http://danlynch.org/blog/wp-content/uploads/2009/03/arch-linux-logo.png
2 http://www.linux-mag.com/s/i/topics/tux.jpg
3 http://techno-geeks.org/wp-
Power Overview
• Battery Duration Calculations
• Power Supply Circuit
• Battery Level Detecting Circuit
– Battery voltage drop
Battery Capacity
• Battery Capacity: 5000mAh
• Initially chosen to maintain at least 3 hours of
operation
• Initial calculations done with worst case scenarios
– Beagle board dissipating power at its maximum rating
– Sensor unit dissipating high amount of power
Power Dissipation (measured)
Battery Duration
Power Supply Circuit
• Supplies different levels of voltage for Sensor and
Microcontroller Units
• Uses Voltage regulators to generate stable voltage
output
• Voltage regulators are chosen to supply sufficient
power (current)
Power Supply Circuit
Battery level Detection
• Voltage for battery drops as power is drawn
• Model relation between voltage and battery
level
• Detect battery level via detecting voltage
• Send Beagle Board signals when voltage drops
under certain level
Voltage vs. Battery level
Estimated state of charge (%)
100 ~ 95
90 ~ 85
80 ~ 75
70 ~ 65
60~55
50 ~ 45
40 ~ 35
30 ~25
20 ~ 15
10 ~ 5
0
open circuit voltage (V)
15.4
15.05
14.9
14.84
14.8
14.76
14.63
14.5
14.18
13.96
13.8
15.6
15.4
Battery Voltage
15.2
15
14.8
14.6
14.4
14.2
14
13.8
13.6
0
2
4
6
8
10
12
Battery level Detection Circuit
Battery level Detection Circuit
Divides Battery voltage by
3 to get voltage available
for comparators
Battery level Detection Circuit
4.92V
Goes low when
Vbattery < 14.76V
4.81V
4.70V
4.65V
Goes low when
Vbattery < 13.95V
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Ethics
• Any guarantees regarding safety will have to be well
tested before they are made to a consumer.
• We need to make sure that there are clear directions
regarding the use of this device, for if used incorrectly, it
could cause more danger than if it weren’t installed in
the first place
• FCC regulations on frequency
1 http://www2.gcc.edu/orgs/IEEE/Images/IEEE_logo.jpg
2 http://1.bp.blogspot.com/-GmKhT1AfKZM/Tukx8BrFEbI/AAAAAAAAAq4/p63_uC-ztlk/s400/EthicsScale.jpg
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Improvements
• Impedance matching
– Especially for antenna
• Better parts (circulator, mixer)
– Reduce leakage
• Decrease resolution
– Increases fps (more reactive image)
Special Thanks To
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Serge Minin
Professor Steven Franke
Professor Jennifer Bernhard
Professor Jont Allen
Skot Wiedmann
Mark Smart
Nihar Gandhi
Wally Smith