#define A 8
#define B 9
#define C 10
#define D 11
#define DT 20

byte coils[4] = {A, B, C, D};

unsigned long step = 0;
byte spoelnummer = 0;

void dostep(byte spoelnummer);

void setup() {
  pinMode(A, OUTPUT);
  pinMode(B, OUTPUT);
  pinMode(C, OUTPUT);
  pinMode(D, OUTPUT);
  digitalWrite(A, LOW);
  digitalWrite(B, LOW);
  digitalWrite(C, LOW);
  digitalWrite(D, LOW);

}

void loop() {
  step = step + 1;
  dostep ( step%4);

}

void dostep(byte spoelnummer) {
  digitalWrite(coils[spoelnummer], HIGH);
  delay(DT);
  digitalWrite(coils[spoelnummer], LOW);
  delay(DT);
}