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Help with rotary encoder/ switch for ADAU1701 on Wondom AMP2 / DSPB-K DSP board

Category: Hardware

Hi, I have been struggling to get external switches or rotary encoders to work on the Wondom AMP2 when programming it using an IPC3.

Whenever I connect up the switch or rotary encoder I cant get a readback value and then it seems to break the whole chip, only working again when I reboot.

Focusing on the switch first because its simpler. 

I have got the switch connected to MP5 on the J3 connector and ground (pin 1 on the J4 connector). When I bridge the switch to ground, all the readbacks and features on the board disable



Edit: additional info for Dave as reply isn't working

Hi Dave, thanks very much for replying, I've been scouring the internet for answers and its all a bit over my head (for now anyway).

I have also tried using an external potentiometer and have not been able to get a successful readback (I have set the onboard ones to 100%), would you mind checking if my wiring is okay, like you say I think I am shorting power to ground (luckily the board seems resilient!)

Yep I agree I had the switch in the wrong place so here is an updated diagram that hopefully makes it clearer as I'm still only getting a readback of 1 when its open or closed.

If the rotary encoder requires soldering I would rather not attempt it, these are the encoders I bought 

Thanks a lot for your help



Edits added to main post
[edited by: ollieb123 at 6:23 AM (GMT -4) on 16 May 2024]

Thread Notes

  • Hello,

    I do not know why this post did not show up as new so I just saw this. 

    You have several issues. The first is a number format issue. The index controlled MUX must have an integer input of 0 or 1 in 28.0 format. It is used as a pointer offset so when the switch is putting out a "1" in 5.23 format it is pointing WAAAYYY far away in memory to some unknown memory address. 

    A rotary encoder is a larger issue. I know there have been posts about it on the forum. I can look for them later. 

    You mentioned MP5 on J3, MP5 is not on J3....  Then you mentioned pin 1 on J4. I wish they documented the actual pin numbers but that might be correct. MP5 does show up on J4. 

    It almost sounds like you are shorting power to ground or some other bad thing. 

    I have several of these boards back home so I can look deeper into this tomorrow. 

    Regarding the rotary encoder. You will have to draw a schematic of how you intend to connect this. You will most likely need pull up resistors. 

    There are a couple of different types of rotary encoders so that will also be important to know what you are using?

    Also, include your SigmaStudio project. It helps. 

    Dave T

  • Hi Dave, thanks very much for replying, I've been scouring the internet for answers and its all a bit over my head (for now anyway).

    I have also tried using an external potentiometer and have not been able to get a successful readback (I have set the onboard ones to 100%), would you mind checking if my wiring is okay, like you say I think I am shorting power to ground (luckily the board seems resilient!)

    Yep I agree I had the switch in the wrong place so here is an updated diagram that hopefully makes it clearer as I'm still only getting a readback of 1 when its open or closed.

    If the rotary encoder requires soldering I would rather not attempt it, these are the encoders I bought though amazon.co.uk/.../B07CMVQHLT

  • Hello ollieb123,

    Sorry for the delayed response. I have a lot of plates spinning. 

    I was thinking of drawing this out as a schematic to prove to you what the problem is but I will just describe it. 

    You MUST remove the existing pots on the board. You cannot dial out the ones on the board. Here is the problem.

    If you set the pot to max clockwise, then the wiper of the pot, which is tied to the AUXADC input pin, will be sitting at the power rail. Only the wiper resistance in series with the 3.3V power. So if you then tie in another pot onto the AUXADC input pin and turn it to the minimum (ground) then you have introduced a short between power and ground via the wipers of the two pots! something will burn up or melt!

    If you set the built in pot to ground then the opposite is the problem, if you dial in your external pot to the max it will be a short between ground and power. 

    If you set the internal pot to 50%, then it is better as far as a short is concerned, but you will have resistances in parallel which will change the curve of the linear pot to be non-linear. I have done this in many designs, put a 10K pot on the wiper to ground and use a linear 10K pot to get a pseudo-log taper. Look at the old Neve recording consoles and you will see that done. 

    So you MUST remove the pots on the board if you want to have the pots be sitting on a faceplate or something like that. I was going to suggest I could make a deal because I have one of these boards with bad pots on them. I could remove them and send it to you but you are out of the country so not a simple thing to do. I use these boards for an oscilloscope lab in my classroom where I teach evening classes. I needed a signal generator with various signals to have something to "see" with a scope. I had a student twist the trim pots so hard that it damaged the internal stops and the pots now spin 360 degrees around. These boards are so low cost that it would cost me more to buy replacement pots than it does to just buy a new board. But I hate wasting an otherwise good board.

    Back to your questions. 

    I will attach a couple of project I have for rotary encoders. They are a little bit more involved but it will give you an idea. 

    The one with micro-controller control features is certainly more complicated but also shows how you can easily limit the index to a table. 

    Also, have you found my YouTube channel yet? 

    Dave T

    2158.ADAU1701 Rotary Encoder with extras.dspproj

    ADAU1701 Rotary Encoder using Up-Down and uC control.dspproj

  • Hi Dave,

    Thanks very much for taking the time to reply, it's very helpful. I'm glad I didn't break the board! No worries about the board, as you say they are quite inexpensive. I've ordered some 10k pots and might end up desoldering the existing ones like you mentioned. I also found this for super cheap store.sure-electronics.com/product/800 so have ordered one as it looks like its a prebuilt version of what I need with some extras.