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I'm using pulseIn on an ESP32 for measuring a frequency between 500 Hz and 10 KHz. I measure both the HIGH and the LOW time, as all simple examples suggest. 95% of the time the result is correct, but sometimes pulseIn returns 0. It can happen on the HIGH or the LOW measure. I'm using GPIO27, which should not be a problem. On a digital scope the signal is very steady and clean.The code is very basic.

const int pulsePin = 27; // Input signal connected to Pin 12 of Arduino

unsigned long Htime;
unsigned long Ltime;
unsigned long Ttime;
float Frequency; // Calculated Frequency

void setup() {
  pinMode(pulsePin, INPUT);
  Serial.begin(9600);
}

void loop() {
  Htime=pulseIn(pulsePin,HIGH);
  delay(10);
  Ltime=pulseIn(pulsePin,LOW);
  Ttime=Htime+Ltime;
  Serial.print(Htime);
  Serial.print(", ");
  Serial.println(Ltime);
  delay(100);
}

The output looks like below:

enter image description here

Of course I can add code to ignore measurements with a 0 result, but any ideas on why they appear?

  • 1
    pulseIn() returns 0 in case of a timeout – Sim Son Sep 20 '19 at 13:44
  • I'm aware of the time-out, but then it will take some time before it results to 0. In this case the 0 result come just af fast as the normal readings. If I disconnect the signal it all return zero, but also the reading becomes very slow. The zero-result above come just as fast as the normal readings. And even if I use the time-out parameter, with like a few seconds, the zero-readings come jus as fast as the normal, so there is no time-out, otherwise I would have to wait a few seconds. – Thiqua Sep 22 '19 at 15:16
  • It might be noise on the signal. If you just want to measure a frequency you can use the counter modules to count pulses in a specific range. This would probably be more precise than you approach – Sim Son Sep 24 '19 at 14:11

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