I am building clock and need a circuit to start a 30 VDC motor off of a component's position and then stop it at another position all automatically. The circuit should run on a 9vdc battery. I would prefer a friction less solution such as the sensor moving past magnets to initiate start and stop signal. I've seen a demo where the circuit on a small circuit board passes a magnet and starts a motor. Then as the motor moves the component in front of another magnet opposite polarity, it shuts down the motor. What is this circuitry and any ideas where to purchase would be great.