Node.js Implementation

JavaScript/README.md

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+Instructions
+------------
+
+1. Connect the Pulse Sensor to the "A0" pin of the Arduino
+2. Burn Standard Firmata to Arduino memory
+3. Navigate to the current directory on the console
+4. Run 'node app.js'

JavaScript/app.js

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+var rate = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+      sampleCounter = 0,
+      lastBeatTime = 0,
+      P = 512,
+      T = 512,
+      thresh = 525,
+      amp = 100,
+      firstBeat = true,
+      secondBeat = false,
+      IBI = 600,
+      Pulse = false,
+      BPM,
+      Signal,
+      QS = false;
+
+var five = require('johnny-five'),
+      board, sensor;
+board = new five.Board();
+
+board.on('ready', function() {
+      sensor = new five.Sensor({
+          pin: "A0",
+          freq: 2
+      });
+
+      sensor.scale([0,1024]).on('read', function() {
+          Signal = this.scaled;
+          calculate_bpm();
+
+          if(QS === true) {
+              console.log('BPM : ', BPM);
+              QS = false;
+          }
+      });
+});
+
+function calculate_bpm() {
+
+            sampleCounter += 2;
+            N = sampleCounter - lastBeatTime;
+
+            if(Signal < thresh && N > (IBI/5)*3) {
+                  if (Signal < T) {
+                        T = Signal;
+                  }
+            }
+
+            if(Signal > thresh && Signal > P) {
+                  P = Signal;
+            }
+
+
+            if (N > 250) {
+
+              if ((Signal > thresh) && (Pulse === false) && (N > (IBI/5)*3)) {
+                  Pulse = true;
+                  IBI = sampleCounter - lastBeatTime;
+                  lastBeatTime = sampleCounter;
+
+                  if(secondBeat) {
+                      secondBeat = false;
+                      for(var i=0; i<=9; i++){
+                          rate[i] = IBI;
+                      }
+                  }
+
+                  if(firstBeat) {
+                      firstBeat = false;
+                      secondBeat = true;
+                      return;
+                  }
+
+
+                  var runningTotal = 0;
+
+                  for(var i=0; i<=8; i++) {
+                      rate[i] = rate[i+1];
+                      runningTotal += rate[i];
+                  }
+
+                  rate[9] = IBI;
+                  runningTotal += rate[9];
+                  runningTotal /= 10;
+                  BPM = 60000/runningTotal;
+                  QS = true;
+              }
+          }
+
+          if (Signal < thresh && Pulse === true){
+              Pulse = false;
+              amp = P - T;
+              thresh = amp/2 + T;
+              P = thresh;
+              T = thresh;
+          }
+
+          if (N > 2500) {
+              thresh = 512;
+              P = 512;
+              T = 512;
+              lastBeatTime = sampleCounter;
+              firstBeat = true;
+              secondBeat = false;
+          }
+}