Stepper

int steps = 0;      // set variable to hold our step position.
int sensorVal = 0;  // set variable to hold our sensor value, and later our delay.

byte coil1 = 4;     // set alias' for the coil pins.
byte coil2 = 5;
byte coil3 = 6;
byte coil4 = 7;

void setup(){
  pinMode(coil1, OUTPUT);  // set coil pins as outputs.
  pinMode(coil2, OUTPUT);
  pinMode(coil3, OUTPUT);
  pinMode(coil4, OUTPUT);

  pinMode(A0, INPUT);      // set analog read pin as an input.
}

void loop(){
  // Lets take a sensor reading, and turn it to a polarised
  // speed between 0 and ~1000 ms.
  sensorVal = analogRead(A0);  //     0 -> 1023
  sensorVal -= 512;            //  -512 -> 511
  sensorVal *= 2;              // -1024 -> 1022
  // so now we have a value, where +ve/-ve holds direction,
  // and absolute value holds the speed.

  // currently, we have a high delay value for high speeds, when we want the opposite. lets flip this,
  // and delay the needed time.
  delay(1023 - abs(sensorVal));

  digitalWrite(coil1, steps==0?HIGH:LOW);  // Now set the coil pins as appropriate:
  digitalWrite(coil2, steps==1?HIGH:LOW);  // the number of the pin to be written
  digitalWrite(coil3, steps==2?HIGH:LOW);  // high is stored in steps.
  digitalWrite(coil4, steps==3?HIGH:LOW);

  // lets set the next pin to come on. this is in the range 0-3, so we will do a modulo-4 to
  // keep this in range.
  if (sensorVal > 0){steps = (steps+1)%4;}  // if the sensor +ve, increase the step by one.
  if (sensorVal < 0){steps = (steps-1)%4;}  // sensor -ve, so decrease the count.
  if (sensorVal == 0) {}  // the sensor was 0, we will neither increase nor decrease the stepper.
}