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 Forum index » DIY Hardware and Software » Arduino
Arduino as a digital pot/matrix mixer etc
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the19thbear



Joined: Apr 19, 2007
Posts: 148
Location: denmark

PostPosted: Sat Oct 20, 2018 12:59 pm    Post subject: Arduino as a digital pot/matrix mixer etc Reply with quote  Mark this post and the followings unread

Ok.
Warning!
I have no experince with code, and I only have basic electronics knowledge, but have built DIY kits in the past and can follow signal flow in a schematic, and can tell a resistor from a pot/transistor etc.

So I have been toying with an idea.
I have an analog device, that does not have memory, but I would love it to have memory:)

Could I use an arduino with a shield to control it?

I want something like this:

Analog device control pot (pot/switch etc) send to arduino, and then to analog device circuit board.
The arduno would be in between.

My idea would be to take a specific pot on the device, and note its ohm value (seems like all pots are 110k lin), and then emulate that on the arduino.
I would then desolder the pot and in its place, would place a pot that is not connected to the device, but goes directly a arduino in port on a shield (or similar). Then the arduino would control a digital pot (or whatever) that is connected to the solder points where the original pot was soldered in.

So basically I want the arduino to function as a digital pot. (many pots and switches actually, about 53 total).
I *DONT* want to digitize any of the devices analog signals. I only want to control them.
What specific shield could be used?
Is the digital pot the most elegant and easy/cheap solution?
Could you point me in the right direction post some links etc, pretty please:)


This is my findings so far:

I looked at the schematic of my device, and sometimes the pots are connected to +15v and other times -5.
I couldnt seem to find a single digital pot that covered from -5 to +15. I guess I would need different pots (some +15 in specific places, and some -5 in other places?). Or maybe it doesnt matter, since the whole +15/-5 i just a matter of polarity?

Look at this as an example:
https://www.mouser.dk/ProductDetail/Microchip-Technology/MCP45HV51T-104E-ST?qs=sGAEpiMZZMsX%252bY3VKDPZyCU7AZzp3iUEYCFgI9JIJlXNbsckjo4zUg%3D%3D

It has a supply voltage of 1,8 to 36 volts.
It also has 256 steps, which is ok. Not amazing, better than normal midi, which has 127 steps.

Would this pot work in cases where it is connected to +15v and -5v?
It doesnt have to go from +15 to-5 in the same connection. The -5 is one pot, the +15v is another pot.

If this could be used, I guess I would move on to the whole coding and hardware aspect.
Since i want to connect about 54 pots/switches to the arduino, what shield should i use?
I'm thinking that i can get around with this, by doing some multiplexing, and not be needing physically 54 inputs?

And then there is the coding part!!! what am i thinking! I know nothing about it!
Heheh:)
I'm trying to find out the cheapest way to get this done, and to see if it makes sens to do at all. It is a hobby project, so i dont mind learning lots of new stuff by doing this.

Thanks again:)
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Grumble



Joined: Nov 23, 2015
Posts: 796
Location: Netherlands
Audio files: 23

PostPosted: Sun Oct 21, 2018 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

In the datasheet you mention there is written:
Quote:
The system can be implemented as dual
rail (±18V) relative to the digital logic ground (DGND).

So it must be possible to cover your needs in the +15 to -5 volt region.
But before you buy a humungus amount of digital potmeters and to keep you from a huge disappointment I think it is a good idea to just buy 2 of these potmeters (or maybe 4 because you can have 4 individual potmeters to one I2C bus ), wire them up, program your arduino or whatever processor you will be using, and get a feeling for what they can handle qua voltages, what is the speed, the cross talk all that kind of things.
And when you feel comfortable about it all, you can expand, buy more pots, go ahead multiplexing the sh*t out of it, and if you feel like it ask more questions as you progress in the diy world.
Good luck!

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Grumble



Joined: Nov 23, 2015
Posts: 796
Location: Netherlands
Audio files: 23

PostPosted: Sun Oct 21, 2018 1:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, btw: If you do want to have that much potentiometers like you stated in your first post, try to find SPI controlled pots, because they are easier to multiplex and faster than I2C ones.
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the19thbear



Joined: Apr 19, 2007
Posts: 148
Location: denmark

PostPosted: Mon Oct 22, 2018 4:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks.
I will need a psu as well though.. I guess I will need a psu that has the same voltages that the circuit has. So a -5v +15v psu.

For the multiplexing thing, adding that many pots etc, will i need an extra shield for the arduino? And what is the smallest arduino i can get by with?

And will i need to filter out hight freq content on each pot, in order to avoid heavy stepping?

Thanks
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Oct 22, 2018 6:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I never work with shields so I don’t know. I usually buy a arduino nano or something similar, solder that on a perfboard and add electronic parts that I need for the module I’m working on.
See below for some youtubes of my synth. Almost every module I made has an arduino in it.
About the filtering: If you use these digital pots to control a voltage, some filtering may be benificial but a good start is also to make smaller steps in a short time so you already have kind of a ramp, so the filtering can be less heavy.
If you use the digital pots as a volume control there is no need to filter, it even could destroy your signal this way.

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the19thbear



Joined: Apr 19, 2007
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Location: denmark

PostPosted: Mon Oct 22, 2018 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

impressive work!Smile
I cant seem to find any SPI pots that will go to+15v

They all have voltage supply of up to 5v.

I'll have to go without SPI it seems (i'll probably get the one I linked to earlier).

And i'm planning on buying the behringer pro one (i'm sure you are familiar with it), and add this once I gets released.

Here is a schem:


Posted Image, might have been reduced in size. Click Image to view fullscreen.

Actually, its of the original, but i'm assuming it will be very close to the original in every way.

I have messed around with the model D already and it's a great sounding machine. I really like what Behringer is doing, but I would really like memory on these little things. (I had a modular as well, a formant elektor DIY synth+many other classic mono/polysynths, but have sold them all over time).

Let me know if you have any thoughts on the project/schematic. Anything I should be aware of etc.

And if you could point me to anything about coding, then it would be much appreciated.

I'll probably get back once i get the synth or when i find new problems.

Thanks a lot so far!
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Wed Oct 24, 2018 5:42 am    Post subject: Reply with quote  Mark this post and the followings unread

I only had a quick glance at the schematic but it looks like you won't need the range for the pots you might think you need.
For example the "AMP SUSTAIN" pot (R1204) is connected in series with a resistor to +15V. since this pot is 100K and the
resistor is 200K the voltage over the pot itself is only 5V. Also a lot of pots could probably be replaced with DACs since they
just provide a (DC) voltage, but if I understand correctly that's something you don't want to do.

I'll hand the mic back over to grumble who seems to be a bit of an expert here when it comes to synths and arduinos.

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the19thbear



Joined: Apr 19, 2007
Posts: 148
Location: denmark

PostPosted: Mon Oct 29, 2018 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahh, ok. Guess i'll have to measure the points to really know.

How is using a dac a better solution?

If its a cheaper solution, maybe i could use that for the DC places, but that might be a mess... using 2 different ways instead of one.

thanks
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PHOBoS



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PostPosted: Mon Oct 29, 2018 9:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I am not saying it's a better solution but to me it seems a little bit like using digital pots is an extra step, which it isn't really.
I think you will be able to get a higher resolution though and I am pretty sure you can get 8 DACs in a single chip, which might
also be cheaper.

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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Oct 29, 2018 3:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Analog Devices has some 40 channel DAC’s...
Just sayin’ Rolling Eyes Very Happy

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