Hi. I'm looking for some sort of sensor set up to use with a Foucault pendulum project I'm working on, but I don't know where to begin. What I need is a sensor set up that will detect when the ball of the pendulum passes through a certain radius (coming and going) and that will also detect when the ball passes through the exact center of its swing. I also need to be able to connect the sensor system to a logic circuit that has already been designed and built. This circuit has two inputs. One input ("A") should trigger whenever the sensor detects the ball at the outer radius, and the other input ("B") should trigger when the ball passes through the exact center of its swing. Both inputs should "flip-flop," going from 0 to 1 or 1 to 0 each time they are triggered. Any sensor using magnetic fields won't work because it will interfere with other elements of the project. Lastly, it would be best if the sensor system is not very expensive. Thank you for your help and I will be happy to supply additional information if necessary if I am able.