Sensors: Rotary Encoders

The above diagram demonstrates two signals in a quadrature relationship as the signals from the two lines of the rotary encoders are. Note that Phase A leads Phase B by 90 degrees when looking from left to right. Looking from right to left the opposite is true. This is directly analogous to the change in signal relationship when the rotary encoder is turned the opposite direction.

This filter circuit helps to stabilize the output of the shaft encoder and reduces noise by introducing pull-up resistors and low pass filters with cut-off frequency of ~ 1.6kHz on each of the two output pins.