[2015-Fall] WNFA lab1 - CamCom

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Mobile and Vehicular Network Lab

[2015-Fall] WNFA lab1 - CamCom

Camera Communication Hsin-I,Wu

2015/3/13

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INTRODUCTION

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VLC

• Visible Light Communication

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Hw1 intro

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TRANSMITTER

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Tx-hardware

• Zigduino x2 →

http://goo.gl/TjM2uQ

• LEDs x2

• Resistors 250Ω x6

• 麵包版 + 線 x1

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Tx-hardware

Notice : there must be resistors ( 電阻 ) in the circuit

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Tx

• message → bytes → behavior of LEDs

• You can use anything to represent bits:

– color, frequency, luminance, waveform, dup lication, ……

– Don’t forget the low sampling rate of cam era (30fps)

• Get extra score if people cannot notice the behavior of LEDs

• Range your score with data rate

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Tx-Zigduino

• Delay()

int ledPin = 13; // LED connected to digital pin 13 void setup()

{

pinMode(ledPin, OUTPUT); // sets the digital pin as output }

void loop() {

digitalWrite(ledPin, HIGH); // sets the LED on delay(1000); // waits for a second digitalWrite(ledPin, LOW); // sets the LED of delay(1000); // waits for a second }

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Tx-Zigduino

• CTC mode

– Clear Timer on Compare (timer == OCRnA) – Generate accurate square waves

• all done by hardware, won’t affected by inte rrupt

• Can simultaneously use all 3 timers easily.

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Tx-Zigduino

• CTC mode

– Set the corresponding bits in TCCRnX(n=1,2,3 X=A,B) re gisters 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)

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Tx-Zigduino

• CTC mode

void setup() {

// use Timer1, set control registers here pinMode(5, OUTPUT);

pinMode(6, OUTPUT);

pinMode(3, OUTPUT);

TCCR3A = _BV(COM3A0) | _BV(COM3B0) | _BV(COM3C0);

TCCR3B = _BV(WGM32) | _BV(CS32) | _BV(CS30);

OCR3A = 32767;

OCR3B = 16383;

OCR3C = 8191;

}

void loop(){

// change OCRnX values to manipulate frequency OCR3A = 32767, OCR3B = 16383, OCR3C = 8191;

delay(10000); // this may not be so accurate OCR3A = 16383,OCR3B = 8191,OCR3C = 4095;

delay(10000);

}

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Tx-Zigduino

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Tx-Zigduino

• CSnX

– n:timer n

– X: 所需的值轉成 2 進制，所對應的第 X 位為 1

• 1/8/64/256/1024

→1/2/3/4/5→0001/0010/0011/0100/0101

• Ex. timer 3 →n=3→CS3X

prescaler=1024→5→0101→ 第 2 位和第 0 位為 1

→_BV(CS32) | _BV(CS30)

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Tx-Zigduino

• CTC mode

– For more details

– https://strawberry-linux.com/pub/doc8266.

pdf – https

://static.squarespace.com/static/511f4f0d

e4b09463c7605f13/t/5275c478e4b07e72f74c74

42/1383449720133/zigduino-v6c-schematic.p

df

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Tx-frequency

stripes to get freq.

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Rolling Shutter

• Global Shutter VS. Rolling Shutter

– A GLOBAL SHUTTER exposes the entire image

r simultaneously.

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Rolling Shutter

• Global Shutter VS. Rolling Shutter

– The rolling shutter actually exposes diff

erent portions of the frame at different

points in time, “rolling” through the f

rame.

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Rolling Shutter

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Tx-luminance

• Fast PWM (with OCRnA top)

– Pulse-width modulation

– Can be used to control duty cycle

– http://arduino.cc/en/Tutorial/SecretsOfArduinoPWM( pins are dif ferent )

– Differences in luminance and ratio of light/dark stripe width

pinMode(6, OUTPUT);

TCCR3A = _BV(COM3B1) | _BV(WGM31) | _BV(WGM30);

TCCR3B = _BV(WGM32) | _BV(WGM33) | _BV(CS32)

| _BV(CS30);

OCR3A = 8191;

OCR3B = 2047; // 25% duty cycle

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Tx-color

• RGB

• HSV

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RECEIVER

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Rx-hardware

• Camera of your smart phone

Notice: 每支手機的相機 fps 不一定都是 30

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Rx

• 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-corr elation, ……

• 3 basic ways : DIP, FFT, auto-correlation

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Rx-an example pseudo code

• for all images

{

read image;

find bounding box // where are the stripes calculate row power

count stripes to get freq. // through DIP or FF T

get output bit by freq.

}

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GRADE

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Grade

• Deadline:4/2(Thur.) 23:59 email to wn@csie.ntu.edu.tw

– Email subject:[WN]lab1_teamXX – [WN]lab1_teamXX.zip

• source code(tx + rx)

• Report(.pdf)

• Demo-4/9(Thur.)

– Please register the demo slot. And come to CSIE R424 at that time.

http://goo.gl/YyM8QF – 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 (20% + 10% for accuracy)

– Report : describe what team members have done(in detail), and probl ems encountered (20%)

– Bonus: real time... (5%)

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特別評分機制

• 90% Lab 團體成績 ( 由各個作業負責的助教決定 )

• 10% 小組互評成績

– 匿名

– 給分範圍為 -2.5 ~ 2.5

– 給分總和需等於 0 (ex 0.25/0.25/-0.25/-0.25)

• 目的

– Report 上的工作分配有時無法準確的表達各個組員

各自的想法，因此添加此機制作參考

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• 情境 1 : 大家都認為彼此付出一樣心力

– 大家彼此都給 0 分，此組員成績 = Lab 團

體成績

• 情境 2 : 1 個 Free Rider

– 大家都給 -2.5 ，共得 -10 ，此人成績 = Lab 團體成績 – 10

– 大家都給救火者 2.5 ，共得 10 ，此人成績 =

Lab 團體成績 + 10

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• 假設 A 組全組認真參與； B 組存在 Free Rider(s)

• A 組在此機制下最高得分只有 90 % ，然而 B 組最高分數卻較高 90% + 10% ，是否不公平？

– A 組最高分確實只有 90 % ，然而學期末總成績將依據常態分佈給分，所以總分高低不是重點

– 課程安排上作業傾向需要五人團隊合作，理論上 B 組的 Lab 表現會較 A 組差，因而得到較低的 Lab 團體成績，即使加上互評成績不見得會拿到較 A 組高的分數

– 假若 B 組救火者有能力將 Lab 表現得與 A 組相當甚至更

佳，那麼最後因為最高分數較高而得到較 A 組佳的成績是實

至名歸

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• Contact to TAs :

– facebook https://www.facebook.com/groups/

wn15spring/

– Email : wn@csie.ntu.edu.tw

– Office hour : Thur. 16:00~17:00@ CSIE R42

4

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APPENDIX

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Zigduino

• First program – Blink.ino

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Zigduino

COMx Zigduino

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Zigduino

• serial port monitor – text I/O

– see Examples 08. Strings

– Use the serial monitor to communicate

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ffmpeg

Ffmpeg.exe

video

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