#define SERIAL_PLOTTER 2
static int outputType = SERIAL_PLOTTER;
// VARIABLES
int pulsePin1 = 0; // Pulse Sensor purple wire connected to analog pin 0
int pulsePin2 = 1; // Pulse Sensor purple wire connected to analog pin 1
int blinkPin1 = 13; // pin to blink led at each beat
int blinkPin2 = 12;
int fadePin = 5; // pin to do fancy classy fading blink at each beat
int fadeRate = 0; // used to fade LED on with PWM on fadePin
// these variables are volatile because they are used during the interrupt service routine!
volatile int BPM; // used to hold the pulse rate
volatile int Signal1; // holds the incoming raw data
volatile int Signal2;
volatile int IBI = 600; // holds the time between beats, must be seeded!
volatile boolean Pulse = false; // true when pulse wave is high, false when it's low
volatile boolean QS = false; // becomes true when Arduino finds a beat.
void setup(){
pinMode(blinkPin1,OUTPUT); // pin that will blink to your heartbeat!
pinMode(blinkPin2,OUTPUT);
pinMode(fadePin,OUTPUT); // pin that will fade to your heartbeat!
Serial.begin(115200); // we agree to talk fast!
interruptSetup(); // sets up to read Pulse Sensor signal every 2mS
// UN-COMMENT THE NEXT LINE IF YOU ARE POWERING The Pulse Sensor AT LOW VOLTAGE,
// AND APPLY THAT VOLTAGE TO THE A-REF PIN
//analogReference(EXTERNAL);
}
void loop(){
diffSignalOutput(Signal1);
Serial.print(",");
diffSignalOutput(Signal2);
Serial.println("");
}
void diffSignalOutput(int signals){
//Serial.print(BPM);
//Serial.print(",");
//Serial.print(IBI);
//Serial.print(",");
Serial.print(signals);
if (QS == true){ // Quantified Self flag is true when arduino finds a heartbeat
fadeRate = 255; // Set 'fadeRate' Variable to 255 to fade LED with pulse
QS = false; // reset the Quantified Self flag for next time
}
ledFadeToBeat();
delay(20); //take a break
}
void ledFadeToBeat(){
fadeRate -= 15; // set LED fade value
fadeRate = constrain(fadeRate,0,255); // keep LED fade value from going into negative numbers!
analogWrite(fadePin,fadeRate); // fade LED
}
And the Interrupt is
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
}
void tryISR(int signals, int blinks){
int N = sampleCounter - lastBeatTime; // monitor the time since the last beat to avoid noise
// find the peak and trough of the pulse wave
if(signals < thresh && N > (IBI/5)*3){ // avoid dichrotic noise by waiting 3/5 of last IBI
if (signals < T){ // T is the trough
T = signals; //keep track of lowest point in pulse wave
}
}
if(signals > thresh && signals > P){ // thresh condition helps avoid noise
P = signals; // 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 ( (signals > thresh) && (Pulse == false) && (N > (IBI/5)*3) ){
Pulse = true; // set the Pulse flag when we think there is a pulse
digitalWrite(blinks,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 (signals < thresh && Pulse == true){ // when the values are going down, the beat is over
digitalWrite(blinks,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
}
}
// 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
Signal1 = analogRead(pulsePin1); // read the Pulse Sensor
Signal2 = analogRead(pulsePin2);
sampleCounter += 2; // keep track of the time in mS with this variable
tryISR(Signal1, blinkPin1);
tryISR(Signal2, blinkPin2);
sei(); // enable interrupts when youre done!
}// end isr