Pulse Sensor Amped adapted for ESP32

Posts: 3
Joined: Sun Jul 30, 2017 7:17 am

Pulse Sensor Amped adapted for ESP32

Postby Gengus_Kahn » Sun Jul 30, 2017 8:00 am

I have used these little pulse sensors on a few platforms, the ESP32 is the latest toy to run it on.

This uses the hardware interrupt and samples the sensor via pin 34 at 2ms, usual data sent to processing plus the display on 0.96" OLED, PWM LED is disabled.

The main PulseSensorAmped Sketch.

Code: Select all

>> Pulse Sensor Amped 1.2 <<
This code is for Pulse Sensor Amped by Joel Murphy and Yury Gitman
    >>> Pulse Sensor purple wire goes to Analog Pin 0 <<<
Pulse Sensor sample aquisition and processing happens in the background via Timer 2 interrupt. 2mS sample rate.
PWM on pins 3 and 11 will not work when using this code, because we are using Timer 2!
The following variables are automatically updated:
Signal :    int that holds the analog signal data straight from the sensor. updated every 2mS.
IBI  :      int that holds the time interval between beats. 2mS resolution.
BPM  :      int that holds the heart rate value, derived every beat, from averaging previous 10 IBI values.
QS  :       boolean that is made true whenever Pulse is found and BPM is updated. User must reset.
Pulse :     boolean that is true when a heartbeat is sensed then false in time with pin13 LED going out.

This code is designed with output serial data to Processing sketch "PulseSensorAmped_Processing-xx"
The Processing sketch is a simple data visualizer. 
All the work to find the heartbeat and determine the heartrate happens in the code below.
Pin 13 LED will blink with heartbeat.
If you want to use pin 13 for something else, adjust the interrupt handler
It will also fade an LED on pin fadePin with every beat. Put an LED and series resistor from fadePin to GND.
Check here for detailed code walkthrough:

Code Version 1.2 by Joel Murphy & Yury Gitman  Spring 2013
This update fixes the firstBeat and secondBeat flag usage so that realistic BPM is reported.


#include <Wire.h>  // Include Wire Set Pins.....
#include <SFE_MicroOLED.h>  // Include the SFE_MicroOLED library

// MicroOLED Definition //
#define PIN_RESET 33  // (dummy my oled only has 4 pins) (req. for SPI and I2C)
#define DC_JUMPER 0   // (dummy my oled only has 4 pins)

// MicroOLED Object Declaration //
// Declare a MicroOLED object. The parameters include:
// 1 - Reset pin: Any digital pin
MicroOLED oled(PIN_RESET, DC_JUMPER); // Example I2C declaration

const int WIDTH=64;
const int HEIGHT=48;
const int LENGTH=WIDTH;

int fadePin = 12;                 // 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 Signal;                // holds the incoming raw data
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 Arduoino finds a beat.

// For the display

int x;
int y[LENGTH];

void clearY(){
  for(int i=0; i<LENGTH; i++){
    y[i] = -1;

void drawY(){
  oled.pixel(0, y[0]);
  for(int i=1; i<LENGTH; i++){
      //u8g.drawPixel(i, y[i]);
      oled.line(i-1, y[i-1], i, y[i]);

void setup(){
  oled.clear(PAGE);                 // Clear the screen
  x = 0;
  pinMode(LED_BUILTIN,OUTPUT);      // pin that will blink to your heartbeat!
  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 

void loop(){
  y[x] = map(Signal, 0, 1023, HEIGHT-1, 0);
  if(x >= WIDTH){
    x = 0;

  sendDataToProcessing('S', Signal);     // send Processing the raw Pulse Sensor data
  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
        sendDataToProcessing('B',BPM);   // send heart rate with a 'B' prefix
        sendDataToProcessing('Q',IBI);   // send time between beats with a 'Q' prefix
        QS = false;                      // reset the Quantified Self flag for next time    
        oled.setFontType(0);             // Set font to type 0
        oled.setCursor(0, 0);           // Set cursor to bottom line
        oled.print("BPM = ");           
        oled.print("  ");

  //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

void sendDataToProcessing(char symbol, int data ){
    Serial.print(symbol);                // symbol prefix tells Processing what type of data is coming
    Serial.println(data);                // the data to send culminating in a carriage return
The Interrupt Setup Sketch.

Code: Select all

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

hw_timer_t * timer = NULL;

void interruptSetup(){     
  // Use 1st timer of 4 (counted from zero).
  // Set 80 divider for prescaler (see ESP32 Technical Reference Manual for more
  // info).
  timer = timerBegin(0, 80, true);
  // Initializes Timer to run the ISR to sample every 2mS as per original Sketch.
  // Attach ISRTr function to our timer.
  timerAttachInterrupt(timer, &ISRTr, true);

  // Set alarm to call isr function every 2 milliseconds (value in microseconds).
  // Repeat the alarm (third parameter)
  timerAlarmWrite(timer, 2000, true);

  // Start an alarm

// Timer makes sure that we take a reading every 2 miliseconds
void ISRTr(){                                 // triggered when timer fires....
  Signal = analogRead(34);                    // read the Pulse Sensor on pin 34 3.3v sensor power......default ADC setup........
  Signal = map(Signal, 0, 4095, 0, 1023);     // Map the value back to original sketch range......
  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

  // 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(LED_BUILTIN,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 

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

}// end isr

Posts: 59
Joined: Thu Aug 17, 2017 5:40 pm

Re: Pulse Sensor Amped adapted for ESP32

Postby JoaoLopesF » Sun Dec 03, 2017 11:51 am

Gengus_Kahn, Hi

Thanks a lot


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