experiment19b.html

<html>
  <head>
    <title>Making Things Smart Experiment 19</title>
  </head>
  <body>
    <pre id="log"></pre>
    <script>
    var logElement = document.getElementById("log");
    console.log = function(s) {
      logElement.innerHTML += s+"\n";
    }

    // The threshold for detecting a change to a 1 or a 0 in the signal
    var THRESH = 0.01;

    // Do we think the input is a 1 or a 0?
    var currentState = 0;
    // How many samples have we been in this state (in samples)?
    var timeInState = 0;

    var currentCode = "";

    function gotCode(code) {
      console.log("Got code "+code);
    }

    // Called when the input changes state
    function changedState(newState, timePassed) {
      if (timePassed > 0.02) {
        // let's assume there was a gap. Handle the last code, and reset it
        if (currentCode!="") gotCode(currentCode);
        currentCode = "";
      }
      // Add a bit only when the signal was high (it's now 0)
      // Since in the last code, 'Hi' was the signal
      //   that changed while 'Lo' was constant
      if (newState == 0) {
        if (timePassed > 0.001) currentCode += "1";
        else currentCode += "0";
      }
    }

    function processAudio(e) {
      var data = e.inputBuffer.getChannelData(0);
      // Now search for changes in value
      for (var i=0;i<data.length;i++) {
        // Did it suddely go high? it's a 1
        if (currentState==0 && data[i]>THRESH) {
          currentState=1;
          changedState(1, timeInState / e.inputBuffer.sampleRate);
          timeInState = 0;
        }
        // Did it suddely go low? it's a 0
        if (currentState==1 && data[i]<-THRESH) {
          currentState=0;
          changedState(0, timeInState / e.inputBuffer.sampleRate)
          timeInState = 0;
        }
        timeInState++;
      }
      if (timeInState > 2000) {
        if (currentCode!="") gotCode(currentCode);
        currentCode = "";
      }      
    }

    function startRecord() {
      window.AudioContext = window.AudioContext || window.webkitAudioContext;
      if (!window.AudioContext) {
        console.log("No window.AudioContext");
        return; // no audio available
      }
      navigator.getUserMedia = navigator.getUserMedia ||
                               navigator.webkitGetUserMedia ||
                               navigator.mozGetUserMedia;
      if (!navigator.getUserMedia) {
        console.log("No navigator.getUserMedia");
        return; // no audio available
      }

      var context = new AudioContext();
      var userMediaStream;
      var inputNode = context.createScriptProcessor(4096, 1/*in*/, 1/*out*/);
      window.dontGarbageCollectMePlease = inputNode;
      inputNode.onaudioprocess = processAudio;

      navigator.getUserMedia({
          video:false,
          audio:{
            mandatory:[],
            optional:[{ echoCancellation:false },
              { googEchoCancellation: false },
              { googAutoGainControl: false },
              { googNoiseSuppression: false },
              { googHighpassFilter: false }
            ,{ sampleRate:22050 /* 44100 */ }]
          }
        }, function(stream) {
          var inputStream = context.createMediaStreamSource(stream);
          inputStream.connect(inputNode);
          inputNode.connect(context.destination);
          console.log("Record start successful");
        }, function(e) {
          console.log('getUserMedia error', e);
      });
    }

    startRecord();
    </script>
  </body>
</html>