//  Sketch by R. Jordan Kreindler, written September 2016, to rotate 
//    a stepper motor using the Half Step Method in a counter-clockwise
//    direction, i.e., opposite from that in the previous sketch

// To do this, the order of the pin assignments is reversed. 
int aPin      = 5; //IN1: first end of the blue and yellow stator coil
int bPin      = 4; //IN2: first end of the pink and orange stator coil
int aPrimePin = 3; //IN3: second end of the blue and yellow stator coil
int bPrimePin = 2; //IN4: second end of the pink and orange stator coil
// We do not connect IN5, IN6, or IN7

int delay1 = 3;

void setup() {
  // Set all pins as output to send output signals from the Arduino 
  //   UNO to the coil windings of the stator
  pinMode(aPin,      OUTPUT);
  pinMode(bPin,      OUTPUT);
  pinMode(aPrimePin, OUTPUT);
  pinMode(bPrimePin, OUTPUT);   

  // Start with all coils off
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, LOW);
}

void loop() {
  // Send current to
  // 1. The aPin
  // 2. The aPin, and the bPin
  // 3. The bPin
  // 4. Then to the bPin and the aPrimePin
  // 5. Then to the aPrimePin
  // 6. Then to the aPrimePin and the bPrime Pin
  // 7. Then to the bPrimePin
  // 8. Then the bPrimePin and the aPin. 
  // Thus producing steps using the half step method

  // 1. Set the aPin High
  digitalWrite(aPin,      HIGH);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, LOW);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds
 
  // 2. Energize aPin and bPin to HIGH
  digitalWrite(aPin,      HIGH);
  digitalWrite(bPin,      HIGH);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, LOW);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds

  // 3. Set the bPin to High
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      HIGH);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, LOW);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds

  // 4. Set the bPin and the aPrimePin to HIGH
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      HIGH);
  digitalWrite(aPrimePin, HIGH);
  digitalWrite(bPrimePin, LOW);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds

  //  5. Set the aPrime Pin to high
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, HIGH);
  digitalWrite(bPrimePin, LOW);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds
  
  // 6. Set the aPrimePin and the bPrime Pin to HIGH
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, HIGH);
  digitalWrite(bPrimePin, HIGH);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds

  // 7. Set the bPrimePin to HIGH
  digitalWrite(aPin,      LOW);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, HIGH);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds
  
  // 8. Set the bPrimePin and the aPin to HIGH
  digitalWrite(aPin,      HIGH);
  digitalWrite(bPin,      LOW);
  digitalWrite(aPrimePin, LOW);
  digitalWrite(bPrimePin, HIGH);
  // Allow some delay between energizing the coils to allow
  //  the stepper rotor time to respond.
  delay(delay1); // So, delay1 microseconds
}