Arduino Tachometer using a Hall Effect Sensor (A3144) to Measure RPM of a Motor

Question

I'm currently trying to set up an Arduino Uno and a Hall Effect Sensor (A3144) to measure the RPM of a motor. I have tested the sensor, and it reads "0" when sensing the magnet, and "1" when the magnet is removed. I have also written code that I thought would work, but when I test my program, nothing appears on the Serial Monitor. If anyone has any ideas of how I can change my coding to get it to work, I would greatly appreciate some advice!

Here is my code:

int sensorPin = 2;            //Hall Effect Sensor at Digital Pin 2
float hall_thresh = 100.0;    //Set number of hall trips for RPM reading

void setup() {
  Serial.begin (115200);      // setup serial - diagnostics - port 
  pinMode (sensorPin, INPUT); // setup pins
}

void loop() {
  // preallocate values for tachometer
  float hall_count = 1.0;
  float start = micros();
  bool on_state = false;

  // counting the number of times the hall sensor is tripped
  while (true) {
    if (digitalRead(sensorPin) == 0) {
      if (on_state == false) {
        on_state = true;
        hall_count += 1.0;
      }
    } else {
      on_state = false;
    }
    if (hall_count >= hall_thresh) {
      break;
    }
  }
  // print information about Time and RPM
  float end_time = micros();
  float time_passed = ((end_time-start)/1000000.0);
  Serial.print("Time Passed: ");
  Serial.print(time_passed);
  Serial.println("s");
  float rpm_val = (hall_count / time_passed) * 60.0;
  Serial.print(rpm_val);
  Serial.println(" RPM");
  delay(1);                   // set delay in between reads for stability
}

Format your code properly. And why would you use floats for counters? Terrible idea. — TomServo
If it never prints anything, it is probably because it is stuck in your while loop. — ocrdu
Maybe add a Serial.print() call inside the while loop to see what it's doing? — Pranav Hosangadi
Hi, I have direct experience with engine RPM sensors and using the Arduino as a DIY ECU. Please let me know what engine you are trying to read from and what the approximate MAX rpm would be. I have posted an answer that should get you going. — edgar_wideman

edgar_wideman edgar_wideman · Accepted Answer · 2020-11-11T22:58:18

Here is a recreation of your code, do not hate me if it doesn't work first try, I just confirmed that it compiles and no debugging done. I have a very similar setup that is working as an engine control unit (ECU) operation on a Teensy 4.0, so obtaining RPM using a similar method is proven to work.

int sensorPin = 3; // interupt pin on UNO, adjust according to board.
unsigned long value = 0;
int hall_thresh = 100;    //Set number of hall trips for RPM reading

unsigned long startTime = 0;
void setup() {
  Serial.begin(115200);
  pinMode(sensorPin, INPUT);

  attachInterrupt(digitalPinToInterrupt(sensorPin), addValue, RISING);
}
void loop() {
  if (value >= hall_thresh) { // Math copied from StackOverflow question. 
    unsigned long endTime = micros();
    unsigned long time_passed = ((endTime - startTime) / 1000000.0);
    Serial.print("Time Passed: ");
    Serial.print(time_passed);
    Serial.println("s");
    float rpm_val = (value / time_passed) * 60.0;
    Serial.print(rpm_val);
    Serial.println(" RPM");
    value = 0;
    startTime = micros();
  }
}
void addValue() {
  value++;
}

Please post your problems if you have any and I will be happy to help with the debugging.

Arduino Tachometer using a Hall Effect Sensor (A3144) to Measure RPM of a Motor

2 Answers