Build Instructions

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• 1

  Step 1

  Link to Pulse Sensor Code:

  http://pulsesensor.myshopify.com/pages/code-and-guide

• 2

  Step 2

  Link to LED Code:

  https://learn.adafruit.com/adafruit-neopixel-uberguide/arduino-library

• 3

  Step 3

  volatile int rate[10]; // array to hold last ten IBI values

  volatile unsigned long sampleCounter = 0; // used to determine pulse timing

  volatile unsigned long lastBeatTime = 0; // used to find IBI

  volatile int P =512; // used to find peak in pulse wave, seeded

  volatile int T = 512; // used to find trough in pulse wave, seeded

  volatile int thresh = 512; // used to find instant moment of heart beat, seeded

  volatile int amp = 100; // used to hold amplitude of pulse waveform, seeded

  volatile boolean firstBeat = true; // used to seed rate array so we startup with reasonable BPM

  volatile boolean secondBeat = false; // used to seed rate array so we startup with reasonable BPM

  void interruptSetup(){

  // Initializes Timer2 to throw an interrupt every 2mS.

  TCCR2A = 0x02; // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE

  TCCR2B = 0x06; // DON'T FORCE COMPARE, 256 PRESCALER

  OCR2A = 0X7C; // SET THE TOP OF THE COUNT TO 124 FOR 500Hz SAMPLE RATE

  TIMSK2 = 0x02; // ENABLE INTERRUPT ON MATCH BETWEEN TIMER2 AND OCR2A

  sei(); // MAKE SURE GLOBAL INTERRUPTS ARE ENABLED

  }

  // THIS IS THE TIMER 2 INTERRUPT SERVICE ROUTINE.

  // Timer 2 makes sure that we take a reading every 2 miliseconds

  ISR(TIMER2_COMPA_vect){ // triggered when Timer2 counts to 124

  cli(); // disable interrupts while we do this

  Signal = analogRead(pulsePin); // read the Pulse Sensor

  sampleCounter += 2; // keep track of the time in mS with this variable

  int N = sampleCounter - lastBeatTime; // monitor the time since the last beat to avoid noise

  // find the peak and trough of the pulse wave

  if(Signal < thresh && N > (IBI/5)*3){ // avoid dichrotic noise by waiting 3/5 of last IBI

  if (Signal < T){ // T is the trough

  T = Signal; // keep track of lowest point in pulse wave

  }

  }

  if(Signal > thresh && Signal > P){ // thresh condition helps avoid noise

  P = Signal; // P is the peak

  } // keep track of highest point in pulse wave

  // NOW IT'S TIME TO LOOK FOR THE HEART BEAT

  // signal surges up in value every time there is a pulse

  if (N > 250){ // avoid high frequency noise

  if ( (Signal > thresh) && (Pulse == false) && (N > (IBI/5)*3) ){

  Pulse = true; // set the Pulse flag when we think there is a pulse

  digitalWrite(blinkPin,HIGH); // turn on pin 13 LED

  IBI = sampleCounter - lastBeatTime; // measure time between beats in mS

  lastBeatTime = sampleCounter; // keep track of time for next pulse

  if(secondBeat){ // if this is the second beat, if secondBeat == TRUE

  secondBeat = false; // clear secondBeat flag

  for(int i=0; i<=9; i++){ // seed the running total to get a realisitic BPM at startup

  rate[i] = IBI;

  }

  }

  if(firstBeat){ // if it's the first time we found a beat, if firstBeat == TRUE

  firstBeat = false; // clear firstBeat flag

  secondBeat = true; // set the second beat flag

  sei(); // enable interrupts again

  return; // IBI value is unreliable so discard it

  }

  // keep a running total of the last 10 IBI values

  word runningTotal = 0; // clear the runningTotal variable

  for(int i=0; i<=8; i++){ // shift data in the rate array

  rate[i] = rate[i+1]; // and drop the oldest IBI value

  runningTotal += rate[i]; // add up the 9 oldest IBI values

  }

  rate[9] = IBI; // add the latest IBI to the rate array

  runningTotal += rate[9]; // add the latest IBI to runningTotal

  runningTotal /= 10; // average the last 10 IBI values

  BPM = 60000/runningTotal; // how many beats can fit into a minute? that's BPM!

  QS = true; // set Quantified Self flag

  // QS FLAG IS NOT CLEARED INSIDE THIS ISR

  }

  }

  if (Signal < thresh && Pulse == true){ // when the values are going down, the beat is over

  digitalWrite(blinkPin,LOW); // turn off pin 13 LED

  Pulse = false; // reset the Pulse flag so we can do it again

  amp = P - T; // get amplitude of the pulse wave

  thresh = amp/2 + T; // set thresh at 50% of the amplitude

  P = thresh; // reset these for next time

  T = thresh;

  }

  if (N > 2500){ // if 2.5 seconds go by without a beat

  thresh = 512; // set thresh default

  P = 512; // set P default

  T = 512; // set T default

  lastBeatTime = sampleCounter; // bring the lastBeatTime up to date

  firstBeat = true; // set these to avoid noise

  secondBeat = false; // when we get the heartbeat back

  }

  sei(); // enable interrupts when youre done!

  }// end isr

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