Hi Phil, The traditional incremental encoder is nothing but two optical interrupters and a wheel with slots cut in it around the perimeter. The two optical interrupters are offset by 1/4 of the slot spacing. As the wheel rotates, the interrupters turn on and off once per slot, but which one leads and which one lags depends on direction of rotation. When the wheel is not rotating, both A and B signals are static, and each can be either high or low depending on the exact position where the wheel stopped. Sometimes there can be some "dithering" where one signal (let's say A) is very close to a transition point and rapidly toggles between high and low. However, in this case, the other signal will always be in the middle of either a slot or the metal solid part between slots and will not be switching. The process of extracting step and direction information from the encoder is called Quadrature Decoding. In quadrature decoding, each edge (rising or falling) of each signal is considered a step. The type of edge (rising or falling) and the level of the other signal (high or low) determines the direction. If B is constant low, for example, and A is dithering, then each rising edge of A will count as a forward step and each falling edge will count as a backwards step, so the overall motion will be zero, just increasing and decreasing by one count like any digital quantity which is near its transition point. Some encoders are implemented differently than this but they are all designed to roughly emulate the behavior of the prototypical optical incremental encoder. Some use mechanical switches. Some use magnetic or capacitive technologies. Sean On Wed, Apr 5, 2017 at 5:04 PM, Phil Keller wrote: > I am looking into a design where I would like to use a single > incremental encoder for two separate controls. In order for me to > accomplish this I need to understand what the outputs (A & B) are held > to when there is no rotation. Are the outputs held OFF (aka open), ON > or one of each based on the last rotation? What happens when the user > rotates the knob very slowly? Is the pulse a fixed width or is it base > on shaft rotational speed? What is the state of the outputs if the > rotation is halted between detents? Is the nominal output state > manufacture dependent or is there a "standard". > > Thanks for any guidance you can provide. > -Phil- > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .