int  a1=1, b1=3, a2=2, b2=4;

void setup() {
pinMode(a1, OUTPUT);
pinMode(a2, OUTPUT);
pinMode(b1, OUTPUT);
pinMode(b2, OUTPUT);


digitalWrite(a1, LOW);
digitalWrite(b2, LOW);
digitalWrite(a2, LOW);
digitalWrite(b1, LOW);
}

void loop()
 {
paso1();
delay(10);

paso2();
delay(10);

paso3();
delay(10);

paso4();
delay(10);
 }
void paso1 ( )
{
digitalWrite(a1, HIGH);
digitalWrite(b2, LOW);
digitalWrite(a2, LOW);
digitalWrite(b1, LOW);
}
void paso2 ( )
{
digitalWrite(a1, LOW);
digitalWrite(b2, HIGH);
digitalWrite(a2, LOW);
digitalWrite(b1, LOW);
}
void paso3 ( )
{
digitalWrite(a1, LOW);
digitalWrite(b2, LOW);
digitalWrite(a2, HIGH);
digitalWrite(b1, LOW);
}
void paso4 ( )
{
digitalWrite(a1, LOW);
digitalWrite(b2, LOW);
digitalWrite(a2, LOW);
digitalWrite(b1, HIGH);
}