motor rpm measurement using hall effect sensor

Place one small magnet on the hub of the motor or any rotating part. Place the hall effect sensor at about 1 to 2 mm distance from the magnet. Tune the refsig value(usually =((max_raw value+min_raw value)/2)). ta da!

code is here. https://github.com/animeshshastry/motor-rpm-measurement-using-hall-effect-sensor

or use ctrl+c and ctrl+v for the following:

 //this code measures the difference between two rising edges of the digitalised signal coming from hall sensor and then prints the rpm.
 //pin A0 is the signal pin
 int refsig = 200; //for converting the analog signal coming from hall sensor to digital through arduino code
 int val;//the digital value of the incoming analog signals
 int prev_val = 0;
 int t, cur_t; //time variables
 void setup()
 {
   Serial.begin(115200);
   pinMode(A0, INPUT);
 }
 void loop()//Measure RPM
 {
   int sig = analogRead(A0); //read raw value of hall sensor
   if (sig > refsig) val = HIGH; //convert it to digital 0,1 form
   else val = LOW;
   if (prev_val == 0 && val == 1) { //check for rising edge
     cur_t = micros();
     Serial.println(1000000 * 60 / (cur_t - t)); //print the rpm
     t = micros();
   }
   prev_val = val;
 }