#define INT_A 2    // control the left motor direction pin D2
#define INT_B 4    // control the right motor direction pin D4
#define left_A 9    // define the left motor speed control pin as D9
#define right_B 5   // define the right motor speed control pin as D5

void setup()
{
  Serial.begin(9600);
  pinMode(INT_A, OUTPUT);          // set the motor control pin as OUTPUT
  pinMode(INT_B, OUTPUT);
  pinMode(left_A, OUTPUT);
  pinMode(right_B, OUTPUT);
}


void loop() {
  front();
  delay(1000);
  back();
  delay(1000);
  left();
  delay(1000);
  right();
  delay(1000);

}//end of loop

// go forward
void front()
{
  digitalWrite(INT_A, LOW);   // control the left motor turn forward
  digitalWrite(INT_B, LOW);  // control the right motor turn forward
  analogWrite(left_A, 200);  // set the two motors’ speed（PWM=200)
  analogWrite(right_B, 200);
}
// backward
void back()
{
  digitalWrite(INT_A, HIGH);  // control the left motor turn backward
  digitalWrite(INT_B, HIGH);   // control the right motor turn backward
  analogWrite(left_A, 200);  // set the two motors’ speed （PWM=200)
  analogWrite(right_B, 200);
}
// turn left
void left()
{
  digitalWrite(INT_A, HIGH);   // control the left motor turn backward
  digitalWrite(INT_B, LOW);   // control the right motor turn forward
  analogWrite(left_A, 100);   // set the two motors’ speed（PWM为100）
  analogWrite(right_B, 100);
}
// turn right
void right()
{
  digitalWrite(INT_A, LOW);    // control the left motor turn forward
  digitalWrite(INT_B, HIGH);    // control the right motor turn backward
  analogWrite(left_A, 100);   // two motors’ speed（PWM为100）
  analogWrite(right_B, 100);
}
// stop
void Stop()
{
  digitalWrite(INT_A, LOW);
  digitalWrite(INT_B, LOW);
  analogWrite(left_A, 0);   // both PWM are 0
  analogWrite(right_B, 0);
}