Arduino Stir Plate (digital speed control)

/*
  Arduino Stir Plate
  Uses PWM to control motor speed
  This is much more efficient and motor friendly than resistive speed controls
  It may also allow slower motor speeds to be achieved
  30 May 08 - Yuri_Rage - www.homebrewtalk.com
*/

int driverPin = 9;  // PWM driver connected to digital pin 9
int potPin = 0;     // potentiometer connected to analog pin 0
int oldValue = 0;   // store an old analog value
int newValue = 0;   // store a new analog value for comparison
float divisor;      // divide analog input by this value
float castFloat;    // for type conversion

/*
   NOTE: Increase minValue to keep the motor from stalling and give higher fidelity adjustment.
         The min value is 0 and will give full range adjustment (including off).
         The max value is 254 and will result in full speed regardless of adjustment.
         A minValue between 20 and 100 should be adequate.
*/
int minValue = 0;  // minimum PWM value - read above

void setup() 
{ 
  divisor = 1024.0 / (255.0 - (float)minValue);  // analog inputs are 10 bit while PWM are 8 bit, so we need some division
  //Serial.begin(9600);                          //uncomment for debugging
} 
 
void loop() 
{ 
  castFloat = (float)analogRead(potPin) / divisor + (float)minValue;  // use the divisor already calculated, then add the min value
  newValue = (int)castFloat;
  if (pow((newValue - oldValue), 2) > 1) { // only change state if the PWM value has changed by more than 1 (simple noise reduction)
    analogWrite(driverPin, newValue);      // make the new PWM value active
    oldValue = newValue;                   // store the new state
    //Serial.print("PWM value: ");         // uncomment for debugging
    //Serial.println(newValue);            // uncomment for debugging
  }
  delay(10);                               // wait a little - no need to run full tilt
}