Rotary shaft encoder - microwave

[Harry Bloomfield, Esq.]

This sets the run time on the microwave oven. Turn clockwise number goes up, anti-clockwise down. Or it should do and often does, but sometimes not. So I am trying to determine why...

It has three terminals at one side, then a ground tag/fixing at either side of the unit. Rotating it there is a slight click.

What sort of encoder might it be, anyone?

[Clive Arthur]

Well, it's a three pin rotary encoder! Myriad types though, but the fault you describe sounds just like a dirty track or wiper. These parts aren't fancy, just a wiper and a couple of segmented tracks.

Best get a spare from the manufacturer or a pattern part.

[Andy Burns]

If the knob spins endlessly in either direction, very likely to be an incremental optical type, has A and B pulse outputs from a 2-bit Gray disc that indicate backwards or forwards step.

select by number of pulses/rotation, whether or not it's clicky, shaft length/diameter, whether it includes a push switch etc

[Clive Arthur]

<snip>

Very unlikely to be optical in consumer goods, just a wiper on segmented tracks, aka a 'mechanical' encoder. Cheaper.

[Clive Arthur]

Or two staggered wipers on one segmented track.

[Harry Bloomfield, Esq.]

Andy Burns explained :

Now sorted and thanks! It was as Clive above suggested, just a mechanical contact encoder, I too was expecting a IR disc encoder. The outside body was identical to this -

but, it was very different internally, rather than three spring contacts, it seemed to have around a 100 spaced around the rotor. I couldn't find my switch cleaner, to I used brake cleaner instead.

Whatever, the cleaner seems to have done the trick. The encoder exibiting the same fault when we bought it from Aldi, around ten years ago, but not often enought to be certain then and it was the last one - so we ignored/worked around the problem all of this time, until recently it became even less predictable.

[Clive Arthur]

Looks like the 'solid' track always has one of the three wipers on it which then connects that to the two segmented track sections in quadrature. Ingenious.

[Harry Bloomfield, Esq.]

I don't have a clue how mine worked, I didn't study it. It seemed to have around 1oo segments on the shaft/rotor, then the rest of the body, still on the PCB, just appearered to be a round metal disk.

No time to investigate, she was wanting her kitchen back :-)