Re: [CAD_CAM_EDM_DRO] MAX speed of an rotary encoder

Patrick J wrote:

>Hi Jon,
>
>
>
>>Flanks? I certainly don't understand you there.
>>
>>
>The encoder outputs 2 squarewaves, when the speed is too high there
>will be no flanks only a high signal.
>

No pulses, I guess is what you mean.

>>You have not told us what encoders you have,
>>
>>
>
>It says 'Point s.r.l' on them and the logo is a circle filled with bent
>lines (arcs)
>'via Zucchi 39 - Cusano M.'
>'Made in italy'
>mod # = WI422B100Z24E12PR/PP
>24V
>thats about it, except for colorcode for the outputs.
>
>

Ahh, here's a clue! 24V. Many encoders with power supply above 5 V are,
indeed open-collector. However, an open-collector drive would be more
likely to stay low if the pull-up was marginal.

>
>
>>what circuitry you are using to interface them,
>>
>>
>
>Opto-couplers to isolate and handle the levelshift down to 5v
>for the PIC MCU. Had pullup to 24v or 12v (tried both)
>

Now, when you say it stays high, is that the output of the encoder
directly, or the output of the optocoupler? Many optocouplers,
especially Darlington ones, are REALLY slow, and the speed you
quote sounds very much in that range. If the signal from the
encoder is actually OK, but the signal OUT of the opto is where the
problem shows up, then you need faster opto-couplers. You might have
to use a phototransistor with heavy load and a booster transistor
after it, to get good speed. There are also logic-out optocouplers
that have very fast receivers for this kind of problem.

Jon