A simple set-up to control one motor speed (PWM) and rotational direction over serial using SN754410 (L293D) motor driver.

Video:

Code:

/*SCHEMATIC USING ONLY ONE MOTOR:
 (N/A MEANS FREE PIN)
 
 5V  N/A  N/A  GND  GND  N/A  N/A  N/A
 |    |    |    |    |    |    |    |
 ------------------------------------
 |            SN754410              |
 ------------------------------------
 |    |    |    |    |    |    |    |
N/A  PIN5 MOT1 GND  GND  MOT2 PIN6 VIN
 
 */

#define motorPinOne 5 //The chosen pin must have PWM
#define motorPinTwo 6 //The chosen pin must have PWM

/* Define the rotational direction of the motor. (0 = clockwise and 1 = counter-clockwise) */
int val = 0;
/* Define the rotational speed of the motor. MUST be between 0 and 255. */
int pulse = 0;
/* Used to store the current rotational direction */
int storage = 0;

void setup() {
  Serial.begin(9600);
  Serial.println("Enter 0 or 1 to choose rotational direction");
  Serial.println("Then enter + or - to increase/decrease the rotational speed.");
  Serial.println("Warning: Rotational speed MUST be between 0 and 250.");
}

void loop() {

  val = Serial.read(); //

  switch (val) {
  case '0':
    clockwise();
    break;
  case '1':
    counterClockwise();
    break;
  case '+':
    pulse = pulse + 10;
    updateSpeed();
    break;
  case '-':
    pulse = pulse - 10;
    updateSpeed();
    break;
  }
}

void clockwise(){
  storage = 0;
  Serial.print("Rotation is clockwise and speed is ");
  Serial.println(pulse);
  analogWrite(motorPinOne,pulse);   // set leg 1 of the H-bridge low
  analogWrite(motorPinTwo,0);
}

void counterClockwise(){
  storage = 1;
  Serial.print("Rotation is counter-clockwise and speed is ");
  Serial.println(pulse);
  analogWrite(motorPinOne,0);   // set leg 1 of the H-bridge low
  analogWrite(motorPinTwo,pulse);
}

void updateSpeed(){
  if (storage == 0){
    clockwise();
  }
  if(storage == 1){
    counterClockwise();
  }
}