// wired connections
#define HG7881_B_IA 10 // D10 --> Motor B Input A --> MOTOR B +
#define HG7881_B_IB 11 // D11 --> Motor B Input B --> MOTOR B -

// functional connections
#define MOTOR_B_PWM HG7881_B_IA // Motor B PWM Speed
#define MOTOR_B_DIR HG7881_B_IB // Motor B Direction

// the actual values for "fast" and "slow" depend on the motor
#define PWM_SLOW 50 // arbitrary slow speed PWM duty cycle
#define PWM_FAST 200 // arbitrary fast speed PWM duty cycle
#define DIR_DELAY 1000 // brief delay for abrupt motor changes

void setup()
{
Serial.begin( 9600 );
pinMode( MOTOR_B_DIR, OUTPUT );
pinMode( MOTOR_B_PWM, OUTPUT );
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
}

void loop()
{
boolean isValidInput;
// draw a menu on the serial port
Serial.println( "-----------------------------" );
Serial.println( "MENU:" );
Serial.println( "1) Fast forward" );
Serial.println( "2) Forward" );
Serial.println( "3) Soft stop (coast)" );
Serial.println( "4) Reverse" );
Serial.println( "5) Fast reverse" );
Serial.println( "6) Hard stop (brake)" );
Serial.println( "-----------------------------" );
do
{
byte c;
// get the next character from the serial port
Serial.print( "?" );
while( !Serial.available() )
; // LOOP...
c = Serial.read();
// execute the menu option based on the character recieved
switch( c )
{
case '1': // 1) Fast forward
Serial.println( "Fast forward..." );
// always stop motors briefly before abrupt changes
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
delay( DIR_DELAY );
// set the motor speed and direction
digitalWrite( MOTOR_B_DIR, HIGH ); // direction = forward
analogWrite( MOTOR_B_PWM, 255-PWM_FAST ); // PWM speed = fast
isValidInput = true;
break;

case '2': // 2) Forward
Serial.println( "Forward..." );
// always stop motors briefly before abrupt changes
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
delay( DIR_DELAY );
// set the motor speed and direction
digitalWrite( MOTOR_B_DIR, HIGH ); // direction = forward
analogWrite( MOTOR_B_PWM, 255-PWM_SLOW ); // PWM speed = slow
isValidInput = true;
break;

case '3': // 3) Soft stop (preferred)
Serial.println( "Soft stop (coast)..." );
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
isValidInput = true;
break;

case '4': // 4) Reverse
Serial.println( "Fast forward..." );
// always stop motors briefly before abrupt changes
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
delay( DIR_DELAY );
// set the motor speed and direction
digitalWrite( MOTOR_B_DIR, LOW ); // direction = reverse
analogWrite( MOTOR_B_PWM, PWM_SLOW ); // PWM speed = slow
isValidInput = true;
break;

case '5': // 5) Fast reverse
Serial.println( "Fast forward..." );
// always stop motors briefly before abrupt changes
digitalWrite( MOTOR_B_DIR, LOW );
digitalWrite( MOTOR_B_PWM, LOW );
delay( DIR_DELAY );
// set the motor speed and direction
digitalWrite( MOTOR_B_DIR, LOW ); // direction = reverse
analogWrite( MOTOR_B_PWM, PWM_FAST ); // PWM speed = fast
isValidInput = true;
break;

case '6': // 6) Hard stop (use with caution)
Serial.println( "Hard stop (brake)..." );
digitalWrite( MOTOR_B_DIR, HIGH );
digitalWrite( MOTOR_B_PWM, HIGH );
isValidInput = true;
break;

default:
// wrong character! display the menu again!
isValidInput = false;
break;
}
} while( isValidInput == true );

// repeat the main loop and redraw the menu...
}