Arduino でモーターを回す

/*
 * Arduino code for SN754410 H-bridge 
 * motor driver control. 
 * copyleft Feb. 2010, Fabian Winkler
 * 
 */
int speedPin = 3; // H-bridge enable pin for speed control
int motor1APin = 6; // H-bridge leg 1 
int motor2APin = 7; // H-bridge leg 2 
int ledPin = 13; // status LED
int speed_value_motor1; // value for motor speed
void setup() {
 // set digital i/o pins as outputs:
 pinMode(speedPin, OUTPUT);
 pinMode(motor1APin, OUTPUT); 
 pinMode(motor2APin, OUTPUT); 
 pinMode(ledPin, OUTPUT);
}

void loop() {
 digitalWrite(ledPin, HIGH); // status LED is always on

 // put motor in forward motion
 digitalWrite(motor1APin, LOW); // set leg 1 of the H-bridge low
 digitalWrite(motor2APin, HIGH); // set leg 2 of the H-bridge high

 // just invert the above values for reverse motion,
 // i.e. motor1APin = HIGH and motor2APin = LOW 

 // control the speed 0- 255
 speed_value_motor1 = 127; // half speed
 analogWrite(speedPin, speed_value_motor1); // output speed as 
// PWM value
}