Camera Communication 2014/3/5
[2014-Fall] WNFA lab1 -
CamCom
Visible Light Communication
Use visible light instead of electromagnetic wave for communications.
Use cameras or light sensors as receivers.
Low sampling rate : typically 30 fps
Rolling Shutter
1 1
Time Row 1
Row 2 Row 3 Row 4 1 1
1 1
1 1
1 1
2 2
2 2
2 2
2 2
3 3
3 3
3 3
3 3
Frequency-shift on-off keying
Each frequency represents a bit string.
width in pixels, w
Time
1 2 3 4 5 6 7 8
LED ON
LED OFF
1
Read Out Time of Row 1Rolling Shutter
Another method – ufsook
Only use 2 frequencies, 30*n and 30*(n - 0.5)
What’s the frame difference ?
30*n : 0, since same phase
30*(n-0.5) : 255 * #pixels
4 3.5 4 3.5
http://w.csie.org/~r01922104/hw1.3gp
Our Tx, Rx hardware
Transmitter : Zigduino + LED
Receiver : Camera
Zigduino = Arduino + Zigbee 3 color
LED
Tx part : Zigduino + LEDs
http://www.csie.ntu.edu.tw/~hsinmu/courses/lib/exe/fetch.php?media=arduino_ins.pdf GND
pins reset
Notice : there must be resistors (電阻) in the circuit
First program – Blink.ino
// Pin 13 has an LED connected on most Arduino boards.
// give it a name:
int led = 13;
// the setup routine runs once when you press reset:
void setup() {
// initialize the digital pin as an output.
pinMode(led, OUTPUT);
}
// the loop routine runs over and over again forever:
void loop() {
digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second
digitalWrite(led, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second
} /* note: you can use analogWrite(led, value) instead */
Tx part
message => bytes => behavior of LEDs
You can use anything to represent bits:
color, frequency, luminance, waveform, duplication, ……
Don’t forget the low sampling rate of camera (30fps)
Get extra score if people cannot notice the behavior of LEDs
Range your score with data rate
human or Zigduino Zigduino
Clear Timer on Compare (timer == OCRnA)
Generate accurate square waves
all done by hardware, won’t affected by interrupt
Can simultaneously use all 3 timers easily.
Set the corresponding bits in TCCRnX(n=1,2,3 X=A,B) registers for mode selection and timer prescaler
Set OCRnX for “frequency”(OCRnA) or “delay”(OCRnB,OCRnC)
Frequency = 16M / prescaler / OCRnA / 2
Additional support : interrupt handler (see document)
CTC mode
CTC mode – sample code
void setup() {
// use Timer1, set control registers here pinMode(11, OUTPUT);
pinMode(10, OUTPUT);
pinMode(9, OUTPUT);
TCCR1A = _BV(COM1A0) | _BV(COM1B0) | _BV(COM1C0);
TCCR1B = _BV(WGM12) | _BV(CS12) | _BV(CS10);
OCR1A = 32767;
OCR1B = 16383;
OCR1C = 8191;
}
void loop(){
// change OCRnX values to manipulate frequency OCR1A = 32767, OCR1B = 16383, OCR1C = 8191;
delay(10000); // this may not be so accurate
OCR1A = 16383,OCR1B = 8191,OCR1C = 4095;
delay(10000);
}
CTC mode
For more details
http://www.atmel.com/Images/doc8266.pdf (register definition)
https://static.squarespace.com/static/511f4f0de4b09463c7605f13/t/5275c478e4b 07e72f74c7442/1383449720133/zigduino-v6c-schematic.pdf
Timer name sizeof registers
Control value (fill TCCRnX)
Prescaler Output pin name
<-> pin in Zigduino
Timer1 16-bit WGM = 4
COM1A/B/C = 1 CS = 1/2/3/4/5
1 / 8 / 64/
256 / 1024
OC1A <-> pin11 OC1B <-> pin10 OC1C <-> pin9
(pin11 need a jumper)
Timer3 16-bit WGM = 4
COM3A/B/C = 1 CS = 1/2/3/4/5
1 / 8 / 64/
256 / 1024
OC3A <-> pin5 OC3B <-> pin6 OC3C <-> pin3
Timer2 8-bit WGM = 2
COM2A = 1 CS = 1~7
1/8/32/64 /128/256/
1024
OC2A <-> pin8
Fast PWM (with OCRnA top)
Pulse-width modulation
Can be used to control duty cycle
http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM ( pins are different )
Differences in luminance and ratio of light/dark stripe width
pinMode(6, OUTPUT);
TCCR3A = _BV(COM3B1) | _BV(WGM31) | _BV(WGM30);
TCCR3B = _BV(WGM32) | _BV(WGM31) | _BV(CS32) | _BV(CS30); // TOP=0xFFFF OCR3A = 8191;
OCR3B = 2047; // 25% duty cycle
serial port monitor – text I/O
see Examples 08. Strings
Use the serial monitor to communicate
Rx part : video processing
video ( -> image ) -> get LEDs behavior-> bytes -> message
Video to image:
ffmpeg –i input.avi ouput%d.jpg
supported by windows, linux, and OS X
Counting Stripes : need some DIP
find LED position, image diff, color histogram, edge detection, Fourier transform, auto-correlation, ……
3 basic ways : DIP, FFT, auto-correlation
Rx part : an example pseduo code
for all images {
read image;
find bounding box // where are the stripes calculate row power
count stripes to get freq // through DIP or FFT get output bit by freq
}
Demo – 3/27 (Thu.)
Please register the demo slot. And come to CSIE R424 at that time.
https://docs.google.com/spreadsheet/ccc?key=0AgYjnPH1HzgydFA3VmJxcDVncEtQY jQySk9sRF9sa0E&usp=drive_web#gid=0
All you should do are :
1. Transmit the character string given by TA 2. Record the videos
3. Decode and get the message
grade :
Tx (20% + 10% for not noticed by human eyes + 10% data rate)
Rx : Video Decode (30% + 10% for accuracy)
Report : describe what you have done, and problems encountered (20%)
We will choose 2 groups to demo in the next class, and their grade will be 100%.
