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- 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 = 530; // used to find instant moment of heart beat, seeded
- volatile int amp = 0; // 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(){ // CHECK OUT THE Timer_Interrupt_Notes TAB FOR MORE ON INTERRUPTS
- // 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
- void getPulse(){ // triggered when Timer2 counts to 124
- Serial.println("GET pULSE");
- 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(D4,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(D4,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 = 530; // 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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