Control circuit for interfacing between the arduino and the slot car track.

Too Fast Too Curious Circuit Diagram

Using python and serial communication we are able to send commands to the arduino to run the different velocity profiles.  The arduino output a pulse width modulated signal to the transistor.  Using a transistor allowed us to get enough power to run the slot car track.  We used a 12V power source hooked directly into the transistor.  One issue we ran into early was the transistor overheating but we solved that by attaching a heat sink.  From the transistor the signal was passed through a relay that we were able to control from a digital pin on the arduino (not pictured in circuit diagram).  The relay could switch the polarity of the signal if we sent a high signal to the relay.  This allowed us to make the car travel backwards and forwards around the track.