How to probe the parameters of a mechanical encoder

Almost all of the rotary encoders I've seen used for instrumentation control, whether mechanical or optical, use a 2-bit Gray code system. The mechanical ones are simple contact-closure types, while the optical ones (continuous or detented) use an LED to illuminate a pair of open-collector (active-pulldown) phototransistors.

If it's a mechanical encoder, you should be able to use an ohmmeter to "beep out" the connections. Turning the control one detent position would cause one of the two switches to change state, while the other remains unchanged. Turning the control another detent position in the same direction will cause the second switch to change state while the first remains unchanged.

Each output is usually one full pulse cycle per four detent positions. If the control isn't detented, you'll have to count up the number of pulses in some measurable angle of rotation and then multiply up to

360 degrees.

If it's a detented optical encoder, the same rules apply, but the "switches" will remain open to external measurement unless you're supplying the necessary current to the LED. There is often (but not always) an internal current-limiting resistor to provide the necessary LED current with a 5-volt supply.

Do you have a service manual / schematic? This could make it clearer whether the encoder is mechanical or optical in nature.

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