Re: Optical shaft encoder question

Jitter with single-channel encoders is pretty common. The jitter occurs
because even with a Schmitt trigger there can be noise from the
photocoupling.

You didn't actually mention that it's single-channel but the description
sounds like it. If that's the case, how about adding another transistor
and LED, and buy either the LS7083 or LS7084 chip from USDigital.com
(http://www.usdigital.com/products/ls7083-ls7084/). They're about $3
each, and have circuitry in them to clean up the signal. And since
you're now working with a quadrature encoder, you'll have 6X4 (or 24)
transistions, which is a little better resolution.

-- Gordon


Mark Haase wrote:
>
> Hey all--
>
> I've been pretty quiet here but I started rebuilding my autonomous rover
> a few weeks ago since I've got some down time (recently graduated
> student about to travel for a month).
>
> I've built a small, tricycle drive robot with a sonar head. For
> odometry, I've glued a 6 CPR optical encoder wheel onto the hub of my
> drive wheel. I used a PNP photointerruptor focused at about 2mm from the
> hub, with a hood made of electrical tape to block out ambient light. The
> output of the phototransistor is squared up through a Schimmt-triggered
> hex buffer. The setup works well, putting out a fairly clean, regular
> pulse train. But there does appear to be a small amount of noise between
> some transitions, as about every 10 pulses or so it counts an extra
> pulse. It seems to be random so I don't think its the encoder disk. I've
> tried adding a bypass cap, but a few different values (.01uf, .1uf, even
> 10uf) didn't seem to have any effect. I'm not an EE so I'm not sure what
> else to try. I'd rather not use a 555 if I can help it, because I'm
> short on space.
.

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