Author Topic: Digital pots to analog effects control unit project  (Read 6684 times)

MetalGuy

Digital pots to analog effects control unit project
« on: December 21, 2005, 10:20:14 AM »
Hi,
Concerning the topic discussed here:

http://www.diystompboxes.com/smfforum/index.php?topic=39959.0

I contacted couple of professionals in the microcontroller field and they agreed to design such a unit - schematics, PCB, code and everything. The total cost of the project will be around $300 USD. In the end we'll have something like Sanamp TRI A.C., JMP-1 or even more versatile control unit. No MIDI for now.
If anyone is interested to share the cost of the project I can go ahead and start the procedure.
Please let me know what you think.

Dave_B

Re: Digital pots to analog effects control unit project
« Reply #1 on: December 21, 2005, 10:44:56 AM »
Is this going to store a bunch of patches?  I know you don't want MIDI, but it's going to suck if you're at a gig and a brownout deletes your programs.  It happened to me.  I realize that adding a sysex dump utility is a big addition,  :)   but it's something to keep on the radar. 

Have you decided what you're using for the pots?
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MetalGuy

Re: Digital pots to analog effects control unit project
« Reply #2 on: December 21, 2005, 11:44:07 AM »
Yes it will be able to store patches. It's all bout that in the first place. I usually use 3 to 5 different sounds so I was thinking about 10 patches for a start. So there'll be an EPROM with stored editable patches.
Because the guys writing the code are not musicians and I don't know s*** about MIDI which means I can't explain them how to include it in the project. The only digital pots around are Microchip's MCP4XXXX series but that's not final.

grapefruit

Re: Digital pots to analog effects control unit project
« Reply #3 on: December 21, 2005, 04:25:43 PM »
Even if they don't know how/couldn't be bothered to do the midi programming I'd get them to put the hardware for midi on the PCB so midi can be added later. It's only an optocoupler and a few resistors. If you use a microcontroller with built in uart use the uart pins for the midi I/O. This will make programming the midi code relatively easy. You'll need some way of selecting MIDI channel and dumping data. Maybe just a DIP switch.

Also, make sure you're aware of the limitations of digital pots. All the microchip ones I'm aware of have a terminal voltage range of GND to VDD. (0V to 5V). If you're using it on 9V powered effects that use a 4.5V virtual GND it might not be of much use. In a circuit I've designed to use the mchip pots I'm running a large section of the circuit on a 5V supply with 2.5V virtual GND.

$300 is bloody cheap. There's no way I'd do it for that.

The Tone God

Re: Digital pots to analog effects control unit project
« Reply #4 on: December 21, 2005, 06:26:48 PM »
I contacted couple of professionals in the microcontroller field and they agreed to design such a unit - schematics, PCB, code and everything. The total cost of the project will be around $300 USD.

Paying others to design and build something for you ? Thats not DIY. For shame. :::waves finger in your direction::: ;)

You are paying "professionals" to develop a system like that and they are only charging $300 ? hmm.

Andrew

Gladmarr

Re: Digital pots to analog effects control unit project
« Reply #5 on: December 21, 2005, 06:45:08 PM »
Yeah, that's weird.  I could see students doing it for $300.  I've been paid to make stuff before.  Does that make me a professional?

MetalGuy

Re: Digital pots to analog effects control unit project
« Reply #6 on: December 21, 2005, 07:18:22 PM »
Well, about DIY you're right but only to a point. The circuits/effects we all build have already been designed - we only kind of ...assemble them. So it's still DIY, maybe half DIY.
The "professionals" are actually really students - friends of a friend of a friend of mine that's why it's so cheap. In the beginnig they were kind of reluctant to do it but I challenged them they couldn't do it and they took it personally... I called them professioanls because they are such compared to me.
As far as I know all digital pots run at 5V/GND which if I'm not wrong limits the input voltage. I'm using  JMP-1 schematic for reference and I don't see any problems with that or may be I can't see them. I'm not specialist in the digital field and I would appreciate any comments and remarks concerning this matter. Moreover the project has't started yet /if at all/ so if it's not a big deal we can add MIDI but I would need a schematic or something. The problem is if it doesn't work I don't know how to fix it.
So if anyone is still interested let me know.
« Last Edit: December 21, 2005, 07:19:54 PM by MetalGuy »

Dave_B

Re: Digital pots to analog effects control unit project
« Reply #7 on: December 21, 2005, 10:59:35 PM »
In theory this isn't that tough a project.  In fact, I'm now wondering why it hasn't been done here already.  The only reason I can think of is that the really easy to implement chips are surface mount. 
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gez

Re: Digital pots to analog effects control unit project
« Reply #8 on: December 22, 2005, 04:09:38 AM »
the guys writing the code are not musicians

Be afraid...be very afraid!  :icon_lol:
"They always say there's nothing new under the sun.  I think that that's a big copout..."  Wayne Shorter

MetalGuy

Re: Digital pots to analog effects control unit project
« Reply #9 on: December 22, 2005, 05:52:19 AM »
Quote
As far as I know all digital pots run at 5V/GND

Well, obviously not all. AD5290 proves it, which makes me think of implementing it directly in an all tube preamp, but then 10k, 50k and 100k don't sound like all tube preamp pot values. What's used in Mesa Triaxis?

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Be afraid...be very afraid!

I'm afraid, believe me, but the deal is to pay for a working according to my requirements product - so I'm not paying only for the code but for a working prototype.

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In theory this isn't that tough a project.  In fact, I'm now wondering why it hasn't been done here already

It's easy for those who know how to do it and I'm sure  some people here can. Why it hasn't been done before I don't know - may be the demand for such a product is not very high as I can see from the number of people discussing it.

Dave_B

Re: Digital pots to analog effects control unit project
« Reply #10 on: December 22, 2005, 08:03:25 AM »
...10k, 50k and 100k don't sound like all tube preamp pot values. What's used in Mesa Triaxis?
It's a little early for me, but if anyone else wants a look-see: http://www.tubefreak.com/schema.htm#triaxis

Quote
It's easy for those who know how to do it and I'm sure  some people here can. Why it hasn't been done before I don't know - may be the demand for such a product is not very high as I can see from the number of people discussing it.
Dunno.  PIC coding isn't hard if you can get your head around it.  Personally, I had a tougher time biasing my Obsidian-M.   :icon_biggrin:  The PIC code I've written so far includes some of what your asking for and I started coding in October. 

What did you give them for requirements on the board size?  Is this going to be rackmounted? 
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petemoore

Re: Digital pots to analog effects control unit project
« Reply #11 on: December 22, 2005, 08:46:08 AM »
 may be the demand for such a product is not very high as I can see from the number of people discussing it...
  Since it 'isn't around'...people don't know what they like until they actually Have 'it'.
  I've typed about this...'there's gotta be a way to'...make an electric pot...without using a sewing machine.
  Once something like this is 'in' something and working, they'll come...because it offers this and more...
  No wafers to wear out, no wipers to get messed up, just other problems that are 'modern' [like for anti lock brakes...that we don't want to know about just yet].
  They allow you to do '  ' function, with no manual 'input', using timers, sensors etc. to initiate '  ' function.
  You can make more than one pot do '  ' at the same times, or with staggered timing.
  It enables us to think about doing things we've not yet thunk about, for example the 'E Pot' phaser, uses no Jfets or light sensors, and the resistances inducing phase sweep can be easily adjusted for...
  These multi effect control footboard pedal monstrosities [the kind with the assignable 'pad' footcontrollers for I/O etc.,  and a treadled pot or two]...well, they need some 'Epot's on 'em I think.
   The ability to slowly and precisely 'ramp up' voltage, a little bit at a time, no more.
  They'll come, if you build it.
  If a 'pot' could be made to automatically go from say 2.7 to 4.4 settings wise, and within a predecided amount of time..tha'td be 'something'.
  An Example of the auto-setting pot function, but the 'long way around' to it is the Cyber Twin, and it's 'ghost-knobs twisters'.
Convention creates following, following creates convention.

MetalGuy

Re: Digital pots to analog effects control unit project
« Reply #12 on: December 22, 2005, 09:05:07 AM »
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PIC coding isn't hard if you can get your head around it.

This is the problem - mathematics and stuf like this are not for my head. I can build and modify analog effects and tube amps but  PIC programming is not my cup of tea.
The board should be as small as possible and yes I'm thinking rack mountable although something more simple like Sansamp TRI A.C. shoud be doable as well. My idea is to be able to connect already existing  effects  to the control unit.  Ihave in mind distortion effects for now but it can be expanded to control other effects as well.

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Since it 'isn't around'...people don't know what they like until they actually Have 'it'

Yor're right. This reminds me of the economics debate whether the demand determines the supply or vice versa.