The phototransistor we use produces current given incident infrared light. This current is sent through a transimpedance amplifier in order to generate a voltage waveform. Since the waveform at this point varies in its center point and peak-to-peak voltages, we add a comparator that will generate a regular squarewave whenever any IR light is detected. We could alternately use a peak detector to sense the point at which maximum IR light is detected, but decided to implement the comparator solution for its simple behavior.
Signal Conditioning for Inductive Sensor (x4)
The racetrack has a current-carrying wire (100mA at 20kHz) that can be used to guide a bot. We use coils to sense this current through the wire, and condition the signal before inputting it into our microcontroller. An RLC Resonator at the coil allows us to be sensitive to signals at 20kHz, and also helps to amplify the signal sensed by the coil. From this resonator, we further amplify the signal with an OpAmp and then rectify the signal before sending it to an ADC input of our microcontroller. We have four inductive sensors - two on each side of the track.