[Michael Hill]

Originally Posted by SeanPerez

do i have to divide the rpm by 360 since my encoder has 360 positions in 1 rotation?

Actually, I just modified my code. I realized I had a mistake:

// Controlling a servo position using a potentiometer (variable resistor) 
// by Michal Rinott <http://people.interaction-ivrea.it/m.rinott> 

#include <Servo.h> 
 
Servo motor1;  // create servo object to control a motor 
Servo motor2;  // ditto
 
int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin 
float dt;
volatile byte rpmcount;
float rpm;
unsigned long timeold;

 
void setup() 
{ 
  motor1.attach(9);  // attaches motor 1 on pin 9 to the servo object 
  motor2.attach(10); // ditto
  attachInterrupt(0, rpm_fun, RISING);
  rpmcount = 0;
  rpm = 0;
  timeold = 0;
  digitalWrite(2, HIGH);
  Serial.begin(9600);
} 
 
void loop() 
{ 
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023) 
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the motor (value between 0 and 180) 
  
  
  if (rpmcount >= 20) {
    dt = (float)(millis() - timeold)/1000;
    Serial.print(dt);
    rpm = rpmcount/dt*60;
    timeold = millis();
    rpmcount = 0;
    Serial.print(" RPM: ");
    Serial.print(rpm);
    Serial.print(" Pot: ");
    Serial.print(val);
    Serial.print("\n");
  }  
  
  motor1.write(val);                  // sets the motor speed according to the scaled value 
  motor2.write(val);
}

void rpm_fun()
{
  rpmcount++;
}

At any rate, when used as an interrupt, it only counts once per revolution.