create binary audio signal for key press

index.js

@@ -1,5 +1,6 @@
 var audioContext;
 var sendButton;
+var textToSend;
 var isListeningCheckbox;
 var microphoneStream;
 var microphoneNode;
@@ -11,6 +12,9 @@ var MAX_DATA_POINTS = 1024;
 
 // 20 to 20,000 - human
 var FREQUENCY_TONE = 18000;
+var FREQUENCY_HIGH = 900;
+var FREQUENCY_LOW = 1200;
+var FREQUENCY_DURATION = 100;
 
 function handleWindowLoad() {
   // grab dom elements
@@ -18,12 +22,41 @@ function handleWindowLoad() {
   isListeningCheckbox = document.getElementById('is-listening-checkbox');
   receivedDataTextarea = document.getElementById('received-data');
   receivedGraph = document.getElementById('received-graph');
+  textToSend = document.getElementById('text-to-send');
 
   // wire up events
   sendButton.addEventListener('click', handleSendButtonClick);
   isListeningCheckbox.addEventListener('click', handleListeningCheckbox);
+  textToSend.addEventListener('keypress', handleTextToSendKeypress);
 }
 
+function handleTextToSendKeypress(event) {
+  var keyCode = event.which || event.keyCode;
+  var bits = keyCode.toString(2)
+    .padStart(8, '0')
+    .split('')
+    .map(Number);
+  sendBits(bits);
+}
+function getFrequency(bit) {
+  return bit ? FREQUENCY_HIGH : FREQUENCY_LOW;
+}
+function sendBits(bits) {
+  var audioContext = getAudioContext();
+  var oscillator = audioContext.createOscillator();
+  var duration = bits.length * FREQUENCY_DURATION;
+  for(var i = 0; i < bits.length; i++) {
+    if(i > 0 && bits[i] === bits[i-1]) continue;
+    var offset = ((i * FREQUENCY_DURATION)/1000);
+    oscillator.frequency.setValueAtTime(
+      getFrequency(bits[i]),
+      audioContext.currentTime + offset
+    );
+  }
+  oscillator.connect(audioContext.destination);
+  oscillator.start();
+  window.setTimeout(function() { oscillator.stop(); }, duration);
+}
 function getAudioContext() {
   if(!audioContext) {
     audioContext = new (window.AudioContext || webkitAudioContext)();