Circuit required, to convert one rotary encoder behavior into another

Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
Hi, I know very little about electronics and researched rotary encoders for a couple of days.

My project is to replace a non working turning knob on an appliance interface. I desoldered the rotary encoder and looked at its behavior
It is of the type where when you click from one indent to the next it will go low on A followed by B ( and vice versa ) and then go back to supply voltage (quadrature encoder). I searched long and far but there is no exact replacement available (PIN distance, mount orientation, shaft length etc. )
So I got a different encoder, a wheel from one of the maker suppliers. This encoder behaves differently. When you go from one indent to the next it will turn A low B high and the next indent A high B low. I am trying to research a circuit where I could make the new encoder behave like the old one. I do know programming, but do not want to use a microcontroller and instead learn how to do this in electronic components. This is about learning for me.
I thought about a RC circuit that pulls A up automatically after it went low, but the encoder has this alternating behavior where the next indent I would need to pull it high ( or something:) )

I saw a Youtube video "How To Use A Rotary Encoder Without Software" where the person shows some tricks with electronic components. It's not the easiest to understand for a beginner and either way his output is not what I need.

Can somebody guide me along how to do this best?

P.S. If I was not clear this is part of an interface board for an appliance where the original encoder is mounted on a round circuit board with 3 cables. Ideally the new encoder and circuit would be just drop in and work with the existing board. It looked to me like the main interface board has some debounce RC filters for A and B. So this would still be active I guess.
 

MrChips

Joined Oct 2, 2009
26,089
Welcome to AAC!

You have described in words how the old and new encoders behave. I think this is doable in hardware but if we had more information we would be in a better position to recommend a solution.

Can you post make and model of the actual applicance?
Do you have part numbers of the old and new encoder?
Can you post pictures of the two?
 

crutschow

Joined Mar 14, 2008
29,785
This encoder behaves differently. When you go from one indent to the next it will turn A low B high and the next indent A high B low.
A quadrature encoder signal allows detection of which way it is rotating.

I don't see how you could do that with your new encoder if both outputs change at the same time, as it seems both outputs have the same information, except one has a 180° phase shift.
I think you need to find another quadrature encoder.
 

MaxHeadRoom

Joined Jul 18, 2013
25,206
What is the resolution of the encoder you have (pulses/Rev?)
It may be possible to construct or replicate the action.
Do you know the detection method used in the original?
 

Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
Thank you. I sure can
The appliance is a dryer Electrolux EIMGD60LSS3 - specifically the silver rotary selector knob is not working
The old encoder is an AEC16BR1E4012 ( if you google it you will find one offer from a medical provider, I was even willing to pay $20, but they cancelled on me. I don't think this is manufactured anymore )
One of the big parts suppliers with M ( not sure they can be mentioned ) has CUI encoders. But the one needed is not stocked with a minimum 1000 order
The new encoder is the ANO https://cdn-shop.adafruit.com/product-files/5001/ANO+Encoder.jpg
 

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Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
A quadrature encoder signal allows detection of which way it is rotating.

I don't see how you could do that with your new encoder if both outputs change at the same time, as it seems both outputs have the same information, except one has a 180° phase shift.
I think you need to find another quadrature encoder.
I am pretty sure direction can be inferred. The demo they have on the website does it. As I said I am a total newbie to all of this. It may be that I didn't know how to adjust or handle the oscilloscope. In the old encoder I saw how A was offset from B. When I looked at it in the new encoder it did look simultaneously. The datasheet though shows an offset. The datasheet though also shows A and B go high, so maybe I am not reading it correctly. Let me take a screenshot from the oscilloscope too. I likely don't know what I am doing.
 

MaxHeadRoom

Joined Jul 18, 2013
25,206
If it is a true quadrature encoder, one square wave is offset by 90° to the other .
At one point, both will be either low or both high, dependent on the actual position,
 

Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
My sincere apologies. I see something very different today after setting the Oscilloscope back to default. I must have done some weird setting somewhere. As I said, this is all new and I only know 3 buttons there. So I do see the phase shift now and A and B go in the same direction. Albeit one click they go down, the other up. So this is still different from the original which only went down and comes up by itself. The images are from 2 consecutive clicks int the same direction
 

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Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
What is the resolution of the encoder you have (pulses/Rev?)
It may be possible to construct or replicate the action.
Do you know the detection method used in the original?
Datasheet for the original has some RC debounce circuit and from there it seems to go into a microcontroller I guess. On the board I see some resistors and caps close to the 3 wire cable ( I think that's what they are anyways ).
 

MaxHeadRoom

Joined Jul 18, 2013
25,206
Normally with a quadrature encoder the actual position is not known at power up,.
There must be some means of establishing where the button was left in the previous usage?
 

Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
So I am looking for some electronics circuit ( likely some logic gate and or flip flop or something ) that can convert the new behavior into the old behavior. Essentially
1 click :
old encoder behavior A low B low then later A high B high
new encoder behavior A low then B low A stays B stays ( I could pull this up I guess as I said in the initial post )
2nd click:
old encoder behavior A low B low then later A high B high ( same as above )
new encoder behavior A high then B high A stays B stays ( I would need the inverse of this I think )
So essentially an inverse on every other click I think.
 

Thread Starter

GUGLHUPF

Joined Apr 3, 2022
14
Yep. Just to be clear I did replace the control unit already. This is not about the easiest way to get to a working appliance. I did that. This is about learning about electronics which I am interested in. I have a software background. When you have new people you let them fix bugs. That's the fastest way to learn. In one week I already learned a lot about electronics, rotary encoders, RC filter circuits etc. I am convinced there is an easy way to interface the new encoder with the old board ( some things I need to research flip flops, multivibrators, logic gates etc. - I know very little/nothing about these ). I thought this forum is suited to help me at east guide me what to research to make this possible. If I misunderstood, my apologies. I searched for circuit forum and this came up.
 
Last edited:

crutschow

Joined Mar 14, 2008
29,785
Have you connected the new encoder to see if it works as is?

If not, than an inverter gate on each output may do the trick.
 
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