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Decoder (#9)
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* decoder test suite, recordings, CI badge

* mocked AudioContext and navigator for webjack test

* adds decoder - not working yet

* fixed promise based tests with blue-tape

* decoder works (as good as Hodor speaks 😶 )

* fixed missing return keyword

* typo in tests

* fixed state machine bugs; __changed frequencies:__ 7350Hz will be attenuated by webRTC codecs, which makes demodulation difficult -> new frequencies: low 2450, high 4900

* new recordings due to changed frequencies

* some recording were too long, call stack size exceeded during tests; now all recordings are done with the AudioRecorder from webaudiodemos.appspot.com (instead of OS specific apps like Audacity)

* extended README

* shortens install commands

* updated build

* skipped the only not working (yet) test
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@rmeister @jywarren
rmeister authored and jywarren committed Jul 15, 2016
1 parent 77c1ffc commit 50ea957
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38 changes: 38 additions & 0 deletions README.md
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@@ -1,6 +1,44 @@
WebJack
====

[![Build Status](https://travis-ci.org/publiclab/webjack.svg?branch=master)](https://travis-ci.org/publiclab/webjack)

WebJack is a JavaScript library that uses [SoftModem](https://github.com/arms22/SoftModem), an Arduino library, to create two-way communication between a browser window and an Arduino. No need to install drivers. Just plug in an audio cable and read/send data from the browser.

## Installation
```
npm install --save webjack
```
or
```
bower install -S webjack
```
If not already done, install the SoftModem Arduino library:
[https://github.com/arms22/SoftModem](https://github.com/arms22/SoftModem)


## Usage
```js
var connection = new WebJack.Connection();

connection.listen(function(data) {
console.log('received: ' + data);
});

connection.send('some data');
```




## Building

webjack.js is built using a Grunt task from the source files in `/src/`, and the compiled file is saved to `/dist/webjack.js`. To build, run `grunt build`. To watch files for changes, and build whenever they occur, run `grunt`.


## Testing

Assuming `tape` is installed globally:
```
npm test
```
272 changes: 258 additions & 14 deletions dist/webjack.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,10 @@ var WebJack = {};

(function(exports){

exports = WebJack;
if (typeof module === 'undefined')
exports = WebJack;
else
module.exports = WebJack;

})(typeof exports === 'undefined'? this['WebJack']={}: exports);

Expand Down Expand Up @@ -73,6 +76,248 @@ var WebJack = {};
};
})();

WebJack.Decoder = Class.extend({

init: function(args) {

var decoder = this;

var DEBUG = false;
var onReceive = args.onReceive;
var csvContent = '';

var sampleRate = args.sampleRate;
var baud = args.baud;
var freqLow = 2450;
var freqHigh = 4900; //7350; > 7000 is to large, will be attenuated

var samplesPerBit = Math.ceil(sampleRate/baud);
var preambleLength = Math.ceil(sampleRate*40/1000/samplesPerBit);
// var pushbitLength = Math.ceil(sampleRate*5/1000/samplesPerBit);

var state = {
current : 0,
PREAMBLE : 1,
START : 2,
DATA : 3,
STOP : 4,

bitCounter : 0, // counts up to 8 bits
byteBuffer : 0, // where the 8 bits get assembled
wordBuffer : '', // concat received chars

lastTransition : 0,
lastBitState : 0,
t : 0 // sample counter, no reset currently -> will overflow
}

var cLowReal = new Float32Array(samplesPerBit);
var cLowImag = new Float32Array(samplesPerBit);
var cHighReal = new Float32Array(samplesPerBit);
var cHighImag = new Float32Array(samplesPerBit);

var sinusLow = new Float32Array(samplesPerBit);
var sinusHigh = new Float32Array(samplesPerBit);
var cosinusLow = new Float32Array(samplesPerBit);
var cosinusHigh = new Float32Array(samplesPerBit);

(function initCorrelationArrays(){
var phaseIncLow = 2*Math.PI * (freqLow/sampleRate);
var phaseIncHigh = 2*Math.PI * (freqHigh/sampleRate);
for(var i = 0; i < samplesPerBit; i++){
sinusLow[i] = Math.sin(phaseIncLow * i);
sinusHigh[i] = Math.sin(phaseIncHigh * i);
cosinusLow[i] = Math.cos(phaseIncLow * i);
cosinusHigh[i] = Math.cos(phaseIncHigh * i);
}
})();

function getMaxOfArray(numArray) {
return Math.max.apply(null, numArray);
}

function normalize(samples){
var max = getMaxOfArray(samples);
for (var i = 0; i < samples.length; i++){
samples[i] /= max;
}
}

function sum(array){
var s = 0;
for(var i = 0; i < array.length; i++){
s += array[i];
}
return s;
}


function demod(samples){
var symbols = [];
var cLow, cHigh;

normalize(samples);

// correlation
for(var i = 0, s = 0; i < samples.length; i++, s++){
cLowReal[s] = samples[i] * cosinusLow[s];
cLowImag[s] = samples[i] * sinusLow[s];
cHighReal[s] = samples[i] * cosinusHigh[s];
cHighImag[s] = samples[i] * sinusHigh[s];

cLow = Math.sqrt( Math.pow( sum(cLowReal), 2) + Math.pow( sum(cLowImag), 2) );
cHigh = Math.sqrt( Math.pow( sum(cHighReal), 2) + Math.pow( sum(cHighImag), 2) );
samples[i] = cHigh - cLow;

if (s == samplesPerBit)
s = 0;
}
// smoothing
for(var i = 4; i < samples.length - 4; i++){
samples[i] = (samples[i-4] + samples[i-3] + samples[i-2]
+ samples[i-1] + samples[i] + samples[i+1]
+ samples[i+2] + samples[i+3] + samples[i+4] )/9;
if (DEBUG) csvContent += samples[i] + '\n';
}
// discriminate bitlengths
for(var i = 1; i < samples.length; i++){
if ((samples[i] * samples[i-1] < 0) || (samples[i-1] == 0)){
var bits = Math.round((state.t - state.lastTransition)/ samplesPerBit);
state.lastTransition = state.t;
symbols.push(bits);
}
state.t++;
}
state.t++;
return symbols;
}

function addBitNTimes(bit, n) {
if (state.bitCounter + n > 8)
throw 'byteBuffer too small';
for (var b = 0; b < n; b++){
state.bitCounter++;
state.byteBuffer >>= 1;
if (bit)
state.byteBuffer += 128;
if (state.bitCounter == 8) {
state.wordBuffer += String.fromCharCode(state.byteBuffer);
state.byteBuffer = 0;
}
}
}

decoder.decode = function(samples){
// var a = performance.now();

var bitlengths = demod(samples);

var nextState = state.PREAMBLE;

for(var i = 0; i < bitlengths.length ; i++) {
var symbols = bitlengths[i];
switch (state.current){

case state.PREAMBLE:
// if (symbols >= 11 && symbols <= 49)
if (symbols >= preambleLength -3 && symbols <= preambleLength + 3) {
nextState = state.START;
state.lastBitState = 0;
state.byteBuffer = 0;
state.wordBuffer = '';
}
break;

case state.START:
if (DEBUG) console.log('START');
state.bitCounter = 0;
if (symbols == 1)
nextState = state.DATA;
else if (symbols > 1 && symbols <= 9){
nextState = symbols == 9 ? state.STOP : state.DATA;
addBitNTimes(0, symbols - 1);
}
else
nextState = state.PREAMBLE;
break;

case state.DATA:
if (DEBUG) console.log('DATA');
var bits_total = symbols + state.bitCounter;
var bit = state.lastBitState ^ 1;
state.lastBitState = bit;

if (bits_total > 11) {
nextState = state.PREAMBLE;
} else if (bits_total == 11){ // all bits high, stop bit, push bit, preamble
addBitNTimes(1, symbols - 3);
nextState = state.START;
onReceive(state.wordBuffer);
state.wordBuffer = '';
} else if (bits_total == 10) { // all bits high, stop bit, push bit, no new preamble
addBitNTimes(1, symbols - 2);
nextState = state.PREAMBLE;
onReceive(state.wordBuffer);
} else if (bits_total == 9) { // all bits high, stop bit, no push bit
addBitNTimes(1, symbols - 1);
nextState = state.START;
} else if (bits_total == 8) {
addBitNTimes(bit, symbols);
nextState = state.STOP;
} else {
addBitNTimes(bit, symbols);
}

if (symbols == 0) // 0 always indicates a misinterpreted symbol
nextState = state.PREAMBLE;
break;

case state.STOP:
if (DEBUG) console.log('STOP');
if (symbols == 1) {
nextState = state.START;
} else if (symbols == 3) {
nextState = state.START;
onReceive(state.wordBuffer);
state.wordBuffer = '';
} else if (symbols >= 2) {
nextState = state.PREAMBLE;
onReceive(state.wordBuffer);
} else
nextState = state.PREAMBLE;

break;

default:
nextState = state.PREAMBLE;
state.bitCounter = 0;
state.byteBuffer = 0;
}
state.current = nextState;
// if ((nextState == state.START) && DEBUG) {
// // console.log(csvContent);
// downloadDemodulatedData();
// }
}
if (DEBUG) csvContent = '';
// console.log('audio event decode time: ' + Math.round(performance.now()-a) + " ms");

if (state.t >= 441000 && DEBUG) { // download demodulated signal after ~10 sec
downloadDemodulatedData();
DEBUG = false;
}
}

function downloadDemodulatedData(){
var blob = new Blob([csvContent], {type: 'text/csv;charset=utf-8;'});
var url = URL.createObjectURL(blob)
var link = document.createElement('a');
link.setAttribute('href', url);
link.setAttribute('download', 'data.csv');
link.click();
}
}
});
WebJack.Encoder = Class.extend({

init: function(args) {
Expand All @@ -81,10 +326,10 @@ WebJack.Encoder = Class.extend({

var targetSampleRate = args.sampleRate;
var sampleRate = 44100;
console.log("target sample rate: " + targetSampleRate);
// console.log("target sample rate: " + targetSampleRate);
var baud = args.baud;
var freqLow = 4900;
var freqHigh = 7350;
var freqLow = 2450;
var freqHigh = 4900; //7350;

var samplesPerBit = Math.ceil(sampleRate/baud);
var samplesPeriodLow = Math.ceil(sampleRate/freqLow)
Expand Down Expand Up @@ -342,7 +587,7 @@ WebJack.Connection = Class.extend({

var connection = this;

var audioCtx = new AudioContext();
var audioCtx = args.audioCtx || new AudioContext();
var sampleRate = audioCtx.sampleRate;
var baud = args.baud;

Expand All @@ -356,9 +601,9 @@ WebJack.Connection = Class.extend({
console.log("-- audioprocess data (" + samplesIn.length + " samples) --");

if (!decoder){
decoder = new SoftModemDecoder(connection.args, rxCallback);
decoder = new WebJack.Decoder({ baud: args.baud, sampleRate: sampleRate, onReceive: rxCallback});
}
decoder.demod(samplesIn);
decoder.decode(samplesIn);
}

function successCallback(stream) {
Expand All @@ -379,6 +624,7 @@ WebJack.Connection = Class.extend({
console.log('navigator.getUserMedia error: ', error);
}

navigator = args.navigator || navigator;
navigator.mediaDevices.getUserMedia(
{
audio: true,
Expand Down Expand Up @@ -408,9 +654,7 @@ WebJack.Connection = Class.extend({

// Sends request for a standard data packet
connection.get = function(data) {
rxCallback = function(bytes){
data(bytes);
};

}

// Sends data to device
Expand All @@ -436,10 +680,10 @@ WebJack.Connection = Class.extend({
// Listens for data packets and runs
// passed function listener() on results
connection.listen = function(listener) {

// connection.history.received.push(data);
// listener(data);

rxCallback = function(data){
listener(data);
connection.history.received.push(data);
};
}


Expand Down
2 changes: 1 addition & 1 deletion examples/index.html
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Expand Up @@ -32,7 +32,7 @@ <h3>Received data:</h3>

connection = new WebJack.Connection({baud: 1225});

connection.get(function(data) {
connection.listen(function(data) {
var log = $('.webjack-log');
log.append(data);
log.append('<br> >');
Expand Down
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