This shield for controlling the direction of rotation of DC motors up to 500 mA with BD135 / 6 and 3 A with TIP31 / 2 was obtained in my book Robotics, Mechatronics and Artificial Intelligence, published in the United States. The high and low, low and high levels at the inputs determine the rotation of the motors. High levels should not be applied simultaneously to the inputs. 3 to 15 V motors can be controlled by this circuit. The control levels at the inputs must be complementary, that is, 01 and 10.