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Comparing an Alps rotary encoder to chinese rip-off

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BreakingOhmsLaw:

--- Quote from: Doctorandus_P on May 26, 2020, 05:30:08 pm ---100nF cap to GND is a very bad Idea.

It is also a common mistake lot's of people make.

Zoom in a bit on your scope, and then look at the discharge time of that capacitor, and calculate the current you draw out of the capacitor, while the switch is closing and may or may not be properly closed.

To limit the current to a safe value for the encoder, you would need to put a resistor in series of at least a few hundred Ohms to 1k.

I once had a 400MHz analog Beast of a scope which had flawlessly working optical encoders.
In my Rigol DS1052E replacement the encoders started failing when it was around 2 months old.

--- End quote ---

It's 10k + 100n

Doctorandus_P:
The 100nF cap is charged through the 10k resistor, so you see a nice RC curve on the positive flank.

On the negative flanks, the capacitor is brutely shorted, and discharged in a single pixel of the scope.
Ceramic caps can supposedly deliver up to 10A when shorted.

BreakingOhmsLaw:
Yes, i see your point and you are right of course .
And I expect that adding caps is often the cause of fast deterioration of encoders.
That said, i expect an encoder to work out of the box as the Alps does formidably.
If you open quality encoders, you will find wipers that are separated into several contacts and sometimes even additionally staggered. All done so they don't bounce all at once, and the contact stays connected.
Cheapo encoders mostly don't have that. In fact, here is a picture of that bad example: single wiper contact as expected.


And of course, the secret sauce is in the contact material.

mikerj:

--- Quote from: Doctorandus_P on May 26, 2020, 05:30:08 pm ---I once had a 400MHz analog Beast of a scope which had flawlessly working optical encoders.
In my Rigol DS1052E replacement the encoders started failing when it was around 2 months old.

--- End quote ---

Apples to oranges.  Optical encoders suffer very little in the way of wear, so provided they are sealed well enough I'd expect a long life.  Anything with wiping contacts is going to suffer wear with use.

thm_w:

--- Quote from: Doctorandus_P on May 26, 2020, 05:30:08 pm ---100nF cap to GND is a very bad Idea.
It is also a common mistake lot's of people make.
Zoom in a bit on your scope, and then look at the discharge time of that capacitor, and calculate the current you draw out of the capacitor, while the switch is closing and may or may not be properly closed.
To limit the current to a safe value for the encoder, you would need to put a resistor in series of at least a few hundred Ohms to 1k.

--- End quote ---

Its not clear if OP is just testing them or has them in circuit. Anyway, discussion here for anyone else curious: https://www.eevblog.com/forum/projects/bourns-encoder-filter-is-the-extra-r-useful-in-practice-are-the-values-good/ with relevant link on second page: http://www.ganssle.com/tem/tem387.html

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