Author Topic: Comparing an Alps rotary encoder to chinese rip-off  (Read 5604 times)

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Offline SiliconWizard

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #25 on: May 28, 2020, 03:06:13 pm »
What do you mean ?, without resistor the encoder will wear out faster ?
I dont see how.

Without a series resistor to the cap, the cap will discharge directly through the contacts each time they are closed. Given the small ESR of a typical ceramic cap, that's a lot of current.
 

Offline madires

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #26 on: May 28, 2020, 03:06:36 pm »
A few years ago I bought a bunch of the cheapest rotary encoders from China I could find as a worst case to check some firmware code. I had to tweak some minor details but I made all work without any hardware filtering. No filter caps allowed because the encoder's A and B lines may be shared with a display. Most of those encoders are ok-ish, but some create nasty glitches. The algorithm I use tracks the A and B signals and checks if they follow the Gray code. If there's any problem the last step is ignored and the algorithm starts again with the next one. When the encoder creates a glitch the user simply has to turn a little bit more until the algorithm sees the correct Gray code sequence. Anyhow, I also prefer ALPS' rotary encoders - no problems at all.
 

Offline Yansi

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #27 on: May 28, 2020, 03:07:56 pm »
What do you think happens with the delicate contact surfaces, if they repeatedly short out a 100nF cap charged to 5V or what?
 

Offline Jan Audio

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #28 on: May 28, 2020, 03:26:04 pm »
I dont know, i.m learning, thank you all.
What i was thinking : the power goes thru, nothing else, wearing comes from the mechanical rotating i was thinking.

So suppose you have a ribbon cable, it is very thin, can it also wear from energy ?, is it not the same ?
 

Offline BreakingOhmsLawTopic starter

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #29 on: May 28, 2020, 03:34:37 pm »
Remember the good old day, when a proper switch had  a drop of mercury in it? Razor-sharp edges, no bouncing.
Did any company ever try to replace the mercury with Galinstan alloy?
 
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Online MarkF

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #30 on: May 28, 2020, 03:37:56 pm »
It's not the energy so much as the unlimited spark across the contacts.
The resistor reduces the current and the size of the spark.

Think "walking across the carpet and touching a light switch".
Does the spark hurt?   That's what your encoder says too.    :-DD
 

Offline SiliconWizard

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #31 on: May 28, 2020, 03:48:30 pm »
To see what happens for yourself: just charge a capacitor with a power supply. For instance to 5V. Then short it on a small piece of metal. Try different kinds of capacitors and different capacitance, and see how it sparks, and what's left at the points of impact on your piece of metal.
 

Offline Jan Audio

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #32 on: May 28, 2020, 04:00:36 pm »
Does the alps have more metal ?
For that price it should be more then 4 times thicker.
I know that chinese will use the minimum ammount that still works.
 

Offline SiliconWizard

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #33 on: May 28, 2020, 04:03:39 pm »
Does the alps have more metal ?
For that price it should be more then 4 times thicker.
I know that chinese will use the minimum ammount that still works.

Contact plating is probably different (thicker - different alloy), spring action too. But still, I would certainly use a comfortable series resistor (10k is typical) to avoid unnecessary wear due to sparks.
 

Offline CatalinaWOW

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #34 on: May 28, 2020, 11:27:43 pm »
You need to think in detail about what is happening to understand how better design helps.  If it was simple erosion at the point of first contact there probably wouldn't be much difference between simple (cheap) designs and the better ones.  But when a contact bounces it generates a spark and crater in one or both contacts.  Metal from the crater is deposited nearby, possibly along with non-conductive ash from lubricants or other contaminants like flux and flux cleaner.  So the next time around there is more surface roughness and more electrical bounce.  The electrical bounce is a combination of contact opening from physical bounce of the contact and opening due to non-conductive material between the contacts.  Splitting the contact into multiple subcontacts (sometimes called fingers) reduces the probability of all elements being opened at the same time.  Often the length of each finger is made different so that they have different bounce frequencies, further reducing the chances of all fingers being off at once.

There are elements of quality control in the equation also.  To my knowledge no one has a complete theory of contact design allowing design based on that theory.  Good companies do have thousands of hours of empirical data on the best combinations of contact geometry, spring pressure, contact metallurgy and other factors that result in good performance.  Lesser suppliers usually have a design that either based on a copy of an existing design, probably without understanding tolerances and required material properties, or have a design that has limited test background and possibly wide variation in product.   In some cases they may know how to do it right, but have been forced to jettison design and process elements to achieve a price goal.
 

Offline BreakingOhmsLawTopic starter

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Re: Comparing an Alps rotary encoder to chinese rip-off
« Reply #35 on: May 29, 2020, 11:17:07 am »
In cheap switches an encoders, you will find mostly just nickel-plated spring steel parts as it is the cheapest material and easy to process.
Good quality stuff will use something like a copper-beryllium alloy. That material has properties that make it ideal for this purpose: It can be bent many more times than steel without fatigue. It has better self-cleaning properties and is non-magnetic, so it does not pick up any scrapings that cause even more bouncing.
Of course the price is higher, and it is challenging in production and work safety because beryllium is very toxic.
Adding nickel, zirconium and cobalt to CuBe alloys can change the electrical and mechical properties, and major manufacturers will likely employ several metallurgists for research.
They will also do 100% automated testing, so something like that encoder from hell from my original post would never see the light of day.
Anyway, you get what you pay for - just be aware where the gremlins lurk.

 


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