Arduino PulseSensor Project

Projects General Guidance
1

Right now I'm trying to make a project using the Arduino PulseSensor to read a user's pulse without using the given PulseSensor library. This is the code I have so far:

#include <Arduino.h>
#include <avr/interrupt.h>
#include <stdint.h>
//  Variables
int PulseSensorPurplePin = 0;   //PulseSensor input, reads signal from sensor
int LED = LED_BUILTIN;   //Arduino Uno R3 built-in LED


int Signal;                //Raw signal from sensor
int Threshold = 510;       //Signal is read from 0-1024, if signal is above 510 it registers as a heartbeat

volatile int bPM = 0;      //initial BPM
volatile int beatCount = 0; //initial beatCount
volatile int timesThrough = 0;  //initial times through

ISR(TIMER1_COMPA_vect) //Timer 1 interrupt handler
{
  timesThrough += 1; //adds 1 to timesThrough

  if (timesThrough == 5) //if we've reached this interrupt 5 times
  {
    bPM = (beatCount * 12); //update bpm
    timesThrough = 0; //reset times through
    beatCount = 0; //reset beatCount
  }

  TCNT1 = 0; //reset Timer1
  OCR1A = 15625; //reset Timer1Compare
}
// The SetUp Function:
void setup() {
  pinMode(LED,OUTPUT);         //set the Arduino LED pin as output
  Serial.begin(9600);         //start Serial monitor
  TCCR1A |= (1 << COM1A0); //toggle OC1A ON COMPARE MATCH
  TCCR1B |= (1 << CS12); //set Timer1 to 1024 prescaler
  TCCR1B |= (1 << CS10); //set Timer1 to 1024 prescalewr
  OCR1A = 15625; //Timer1 Compare Number
  TIMSK1 |= (1 << OCIE1A); //Timer 1 Output Compare A Match Interrupt Enable
  TCNT1 = 0; //set Timer1 to 0

}

// The Main Loop Function
void loop() {

  Signal = analogRead(PulseSensorPurplePin);  //read raw data from PulseSensor

  if(Signal > Threshold){           //if the signal is a heartbeat                
    digitalWrite(LED,HIGH); //turn on Pin
    beatCount += 1; //add 1 to beatCount
    delay(50); //delay 50 ms
    Serial.println(beatCount); //print the beatCount to console, only here for testing
  } else { //if the signal is not a heartbeat
    digitalWrite(LED,LOW);             //turn off LED  
  }

}

This is a very rough draft, but I did have some questions if anyone of you could help me through. The Interrupt handler that I created never actually does anything. Does anyone know if I wrote the handler incorrectly where it wouldn't function? Also, when getting the beatCount, the output is greater than one because the PulseSensor returns multiple values that are above the given threshold. Is there a way for it to just read the first one? I've tried using the delay() function but it doesn't seem to work, so is there another way around it?

2 
  TCCR1A |= (1 << COM1A0); //toggle OC1A ON COMPARE MATCH
  TCCR1B |= (1 << CS12); //set Timer1 to 1024 prescaler
  TCCR1B |= (1 << CS10); //set Timer1 to 1024 prescalewr

You should always initialize the timer registers to zero before ORing in control bits. You never know what the boatloader or startup processes might leave in the registers of such peripherals. Some Arduino cores assume that Timer1 will be used for PWM, and set it up accordingly.

3

Ok I'm going to try that. Are there any other glaring errors that you see?

4

I did not look past the obvious error mentioned.

5

Any changing of volatile variable in the main code must be done atomically. In case you need to do something with volatile in the loop() - use the local copy.

6

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