INDEX

The mosfet used is IRF540. Mos have better switching speed. It is used inside L293D. Here DC motor is running at 17V , which is greater than the maximum allowed voltage of DC motor. Higher voltage, greater the speed will be. So when first sensor S1 goes to black strip the voltage across the
motor will be 4*3.3V=13.2V. If the sensor4 goes to black then voltage across the motor will be 3.3V. What will happen if we use another mosfet to short between Vin and ground so that both ends will be shorted for the motor and motor will stop. But this case is somewhat dangerous and the resistor, R should have enough power rating to carry that whole current,because whole current flow through the resistor.