Measure of Duty Cicle of a PWM signal

Other Hardware 3rd Party Boards
7

Also, if you just check frequency, skipping duty cycle, and completely forgo using interrupts, you can measure up to 60-ish KHz. With a regularly timed event, the interrupt code that runs behind the scenes interferes, and actually slows things down near the physical limits of the machine.

const byte inputPin = 2;  // INT.0

boolean inputState = false;
boolean lastInputState = false;
long count = 0UL;

unsigned long previousDisplayMillis = millis();
const long displayMillis = 500L;

void setup() {
  pinMode(inputPin, INPUT_PULLUP);

  Serial.begin(115200);
}

void loop() {
  inputState = PIND & 4;  //  faster than: inputState = digitalRead(inputPin);
  if (inputState != lastInputState) {
    count++;
    lastInputState = inputState;
  }

  // --------- Run this code every *half* second ------------------
  if (millis() - previousDisplayMillis >= displayMillis) {
    previousDisplayMillis += displayMillis;

    Serial.print(count);   //   *** SERIAL PRINT ***
    Serial.print(" Hz");   //   *** SERIAL PRINT ***
    Serial.print('\n');    //   *** SERIAL PRINT ***
    
    count = 0UL;

  }
}