Re: Stepper motors as encoders

--- In CAD_CAM_EDM_DRO@y..., ballendo@y... wrote:

> Hi,
>
> There was an article about using steppers as encoders in one of
> the "popular electronics" (they've changed names/ownership so much

in

> the last few years I can't keep up) magazines within the last few
> years.
>
> I believe you can get more than 100ppr if you "count" all the
> transitions... I think schmitt triggers were involved in the circuit
> in the article.
>
> Hope this helps.
>
> Ballendo

Is this the article you are thinking of?

Stepper Motors as Shaft Encoders, by Neil W Heckt,
Electronics Now, February 1994, pages 53-58.

He includes a simple comparator circuit (6 r's, 1 c , two signal
diodes and 1/4 of a lm339); you need two of these circuits for one
stepper.

he states that while you get 400 steps/rev when you are driving a .9
degree stepper, when you use it as an encoder, it only outputs 100
pulses/rev, although it also gives direction information.

> --- In CAD_CAM_EDM_DRO@y..., grant.fair@s... wrote:
> > I am thinking of playing with stepper motors as shaft encoders.

Has

> > anyone had any luck with this approach?
> >
> > In practical terms, 100 pulses per revolution is the best
> resolution
> > which would be available. The main virtue of this approach would

be

> > low cost, since .9 degree/steppers (which give only 100 ppr) seems
> to
> > be the smallest step size widely available from surplus sources,
> where
> > they are available in the $2 range. The electronics to interface a
> > stepper so it outputs 5V pulses is cheap - 2 comparators, and a

few

> > R's, C's and diodes, plus a 5V power supply.
> >
> > Any comments? Would 100 ppr have any value with DRO's? Of course
> > greater resolution could be achieved mechanically.

Grant