Using IR sensor and arduino to count RPM

Other Hardware Sensors
3

I've approached this with a multiplier rather than a bunch of math in the loop.
Heres my example code I refer to when I forget :slight_smile:

#define TacometerPin 2 // Must be pin 2 or 3

// My Encoder has 400 Clock pulses per revolution
// note that 150000.0 = (60 seonds * 1000000 microseconds)microseconds in a minute / 400 pulses in 1 revolution)
#define Multiplier 150000.0 // don't forget a decimal place to make this number a floating point number

volatile uint32_t _deltaTime; // Delt in time
volatile uint32_t _lastTime; // Saved Last Time of Last Pulse
volatile uint32_t _Time;

void CaputreDeltaT() {
  _deltaTime = (_Time = micros()) - _lastTime; 
  _lastTime = _Time;
}
void setup() {
  Serial.begin(115200); //115200
  pinMode(TacometerPin, INPUT);

  attachInterrupt(digitalPinToInterrupt(TacometerPin), CaputreDeltaT, RISING);
}

void loop() {
  float DeltaTime;
  float SpeedInRPM = 0;
  // Serial print is slow so only use it when you need to (10 times a second)
  static unsigned long SpamTimer;
  if ( (unsigned long)(millis() - SpamTimer) >= (100)) {
    SpamTimer = millis();
    noInterrupts ();
    // Because when the interrupt occurs the EncoderCounter and SpeedInRPM could be interrupted while they
    // are being used we need to command a "hold" for a split second while we copy these values down. This doesn't keep the
    // interrupt from occurring it just slightly delays it while we copy values.
    // if we don't do this we could be interrupted in the middle of copying a value and the result get a corrupted value.
    DeltaTime = _deltaTime;
    _deltaTime = 0; // if no pulses occure in the next 100 miliseconds then we must assume that the motor has stopped this allows a speed of zero to occure
    interrupts ();
    SpeedInRPM = Multiplier / DeltaTime; // Calculate the RPM 
    Serial.print(SpeedInRPM , 3);
    Serial.print(" RPM");
    Serial.println();
  }
}

Z