Sensors

[Michael Hill]

When it comes to encoders, a quadrature encoder is particularly useful. If you take a normal (not magnetic, but light-based) encoder apart, you'll find a light source, an "encoder wheel" with a bunch of holes and a light sensor. Basically, the light shines through the holes. When the wheel spins, the receiver counts how many holes have been seen. Normally, the light sensor can't tell if the wheel is spinning forward or backward, but a quadrature encoder has another light sensor and another set of holes on the wheel that are offset from the first set. There are four distinct "states" the encoder can be in, so it knows if it's counting up or down.