// Motor A connections
int enA = 9;
int in1 = 8;
int in2 = 7;
// Motor B connections
int enB = 3;
int in3 = 5;
int in4 = 4;

int speed = 0;
void setup() {
	// Set all the motor control pins to outputs
	pinMode(enA, OUTPUT);
	pinMode(enB, OUTPUT);
	pinMode(in1, OUTPUT);
	pinMode(in2, OUTPUT);
	pinMode(in3, OUTPUT);
	pinMode(in4, OUTPUT);
	
	// Turn off motors - Initial state
	digitalWrite(in1, LOW);
	digitalWrite(in2, LOW);
	digitalWrite(in3, LOW);
	digitalWrite(in4, LOW);

	digitalWrite(enA, HIGH);
	digitalWrite(enB, HIGH);
}

void loop() {
//accelerate motor
for (speed = 0; speed < 255; ++speed) {
		digitalWrite(in1, 0);
		digitalWrite(in2, 1);
		analogWrite(enA, speed);
		digitalWrite(in3, 0);
		digitalWrite(in4, 1);
		analogWrite(enB, speed);
		delay(50);
	}
for (speed = 0; speed < 255; ++speed) {
		digitalWrite(in1, 1);
		digitalWrite(in2, 0);
		analogWrite(enA, speed);
		digitalWrite(in3, 1);
		digitalWrite(in4, 0);
		analogWrite(enB, speed);
		delay(50);
	}

}