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Optical encoder problems !

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schneiderj

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Hello,

I am using an optical encoder to monitor the speed of a rotor. It is an Avago one, AEDA-3300 serie.
I use it recommended into the documentation from Avago :

**broken link removed**


But after one rotation of the axe I have more than expected return increment from optical encoder. I take a look on the signal, first just at PIN INT0 and INT1 ot the microchip 18F4520, with a logical encoder and an oscilloscope. I obtain :

**broken link removed**


I take a closer look on the value from optical encoder itself and with the value after processing by the DS26C32AM :

**broken link removed**


We can see that some signal modification are strange (if I can said that) : it's look like perturbation of signal.

So now my question : is that normal or not ? How can I solve that issu to have the correct time sampling and furthermore angular speed ?

Thanks you for your help,
Jean-Marie
 
i see there are glitches in your signals.. there are many solutions to that, mainly software solutions. could you specify on those pictures which line is what? e.g. in figure A, what is D5, D6 and D7?

also could you post your circuit here?
 
Thanks for your reply.

D5 is signal formed by line receiver from A+ and A-. This signal A is connected to INT0 pin (RB0) of a 18F4525.
D7 is signal formed by line receiver from B+ and B-. This signal B is connected to INT1 pin (RB1) of the same 18F4525.

D6 is the clock signal used to step the motor driver. The circuit is in the pdf file, but encoder is not on it as well as DS26C32AM (same circuit as Avago data sheet).

Hop this help to understand my question.

Jean-Marie
 

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  • Vis Sans Fin Schema Eagle.pdf
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mhhh still feels those spikes are the problem, did you try to add some low pass R/C filters on the A and B lines? the glitch frequency seem so much higher than the main signal that it can easily be discarded
 
You need to see if those signals are corrupted coming out of the encoder. If they are clean, then you have a problem with shielding in your cables. If they are glitchy from the decoder, then you have a bigger problem.
 
Thanks you for your reply !

For the moment I would like to avoid filter as I have to run the motor at quit different speed.

How can I know if the issue is coming from the shielding of cable ?

An other interesting observation : when the clock which control motor speed, is very fast I obtain a quite nice profile :

**broken link removed**

What did you thinks ?

Jean-Marie
 
Measure the signal at the motor with the cables disconnected. One thing you can do is to capture the position signals with the clock you are driving with. That way, you can save the pulses before the glitches show up.
 
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