In article om,

I'm sure that limits stepper motors to certain uses, but I think this
thread/post may be incorrectly titled. Unless I misunderstand the intended
application, I don't think a "position encoder" is what he is looking for.
Rather he wants something that, when rotated, feeds pulses to an up/down
counter for frequency synthesis. The position of the shaft is not important
as long as its rotation can be used to generate pulses for the counter.

Roger

Roger:

Yes you're right, that's exactly what I'm looking for... any ideas as
to where I might get such a beast?

Usually known as a "rotary encoder". They normally have two outputs,
in a phase-quadrature arrangment. These can be decoded to create
up/down/clock pulses using dedicated ICs (HP makes 'em), or via a small
collection of discrete TTL logic chips, or via a simple software
routine in a PIC micro or similar (which is how I'd probably do it
these days... I wrote a simple state-table routine for an 8051 some
years back which worked out quite well).

You'll probably want at least 64 counts per revolution, and probably
256, to get a nice smooth "feel" to the synthesizer tuning. Most such
use an optical code wheel and a pair of optosensors.

Digi-Key catalog lists quite a few such (all with their own shafts,
ready for panel mounting), but they aren't cheap. Mechanical rotary
encoders are less expensive, but less precise (fewer counts per
revolution) and possibly not as reliable or long-lived since they use
mechanical contacts.


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