/* =========  BASIC MASTER CLOCK IMPULSE TEST  =================
   Coil is energised for {PULSE_MS} ms via ENA every {STEP_MS} ms
*/

const int IN1 = 7;
const int IN2 = 8;
const int ENA = 9;

const uint16_t PULSE_MS = 120;   // coil on-time
const uint16_t STEP_MS  = 1000;  // period (1 Hz test)

unsigned long lastStep = 0;
bool polarity = false;

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(ENA, OUTPUT);

  digitalWrite(ENA, LOW);
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
}

void loop() {
  unsigned long now = millis();

  if (now - lastStep >= STEP_MS) {
    lastStep = now;
    polarity = !polarity;

    // set polarity
    digitalWrite(IN1,  polarity);
    digitalWrite(IN2, !polarity);

    // coil on
    digitalWrite(ENA, HIGH);
    delay(PULSE_MS);

    // coil off
    digitalWrite(ENA, LOW);
  }
}