I am trying to read the pulses of the coil and calculate the RPM on an old (86) Vanagon. I found a few topics about simular projects and tried to learn from them. I am using Arduino NANO 33 BLE for the project and the circuit I build for it is based on an H11L1M (Schmitt Trigger Output Optocoupler). Please see attached schematics of the circuit. I am getting very clean pulses on the output side (see attached photo) but I am not sure I am reading the correct information as the frequency is not changing when I am raving the engine. It stays the same. Any thought on what can it be? The last photo (sorry about the reflections) is how the input signal looks like. The software I developed read an average of 40 pulses per 100 ms using interrupt.
Here is the code. The code works fine when I am generating square signal with another Arduino board.
const int hallPin = 3;
volatile int rpmcount = 0;
int hallState = 0;
int lasthallState = 0;
int rpm = 0;
void setup() {
Serial.begin(9600);
pinMode(hallPin, INPUT);
}
void loop() {
hallState = digitalRead(hallPin); //Reads current hall state
if (hallState != lasthallState) { //if current hall state is different than last hall state then:
if (hallState == HIGH) { //check if current hall state is HIGH, if yes then:
rpmcount = 0; // set number of interrupts to 0, to begin counting
attachInterrupt(digitalPinToInterrupt(hallPin), rpm_fan, FALLING)
delay(200); //wait 100ms, it will run rpm_fan during that time and count LOWs on pin 3
detachInterrupt(digitalPinToInterrupt(hallPin)); //detach interrupt for calculating
rpm = rpmcount * 5; // convert to Hz
Serial.print(rpm)
Serial.println();
}
delay(13);
}
lasthallState = hallState;
}
void rpm_fan() { /* this code will be executed every time the interrupt 0 (pin2) gets low.*/
rpmcount++;
}
