Theory of Rotary Encoder Operation
A rotary encoder typically has 2 outputs. These outputs emit signals that are 90 degrees out of phase with respect to each other. The output signals may be square wave or sine wave. Sine wave outputs are typically used in higher resolution encoder applications. For simplicity, we will talk about square wave output encoders in this application note.
Here is a typical rotary encoder:
Although this looks like a potentiometer, it has infinite rotation. You can turn it in either direction without hitting an end point.
Inside, the encoder, there is typically a slotted disc and 2 optical interrupters.
Here is a typical optical interrupter: Here is a slotted disc:
Figure 1 shows the Two opto interrupters are mounted on the slotted disk. As the slotted disk turns, the light beam between the LED and the photo transistor of the opto interrupters are connected and disconnected. This results in a pulse outputs from each of the optointerrupters:
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