#include <Stepper.h>
#define STEPS 32 // 40 - 60 Steps for Opel Tacho
#define SPEED 7000 // Speed in Rounds per Minute
Stepper stepperSPEED(STEPS, 8, 10, 9, 11);
int valSPEED = 0;
int previousSPEED = 0;
int pwm=9;
int pot=A0;
float value=0;
int percent;
float rev=0;
int rpm;
int oldtime=0;
int time;
void isr() //interrupt service routine
{
rev++;
}
void setup()
{
  Serial.begin(9600);
  stepperSPEED.setSpeed(60);
}
void loop()
{
delay(150);
detachInterrupt(0);           //detaches the interrupt
time=millis()-oldtime;        //finds the time
rpm=(rev/time)*60000;         //calculates rpm
oldtime=millis();             //saves the current time
rev=0;
value=analogRead(pot);        //reads the speed control POT
value=value/2;
analogWrite(pwm,value);       //sets the desired speed
percent=(value/255)*100;      //finds the duty cycle %
attachInterrupt(0,isr,RISING);
valSPEED = rpm/333;
Serial.println(valSPEED-previousSPEED);
stepperSPEED.step(-((valSPEED - previousSPEED)/10));
previousSPEED = valSPEED;
}