I have an Arduino on the way and my plan is to use it to generate programmed control voltage (CV) for my modular synthesizer.

My question is in regards to the voltage output on the PWM. I know the synth gear will take as much as 15v. The Arduino PWM outputs will do up to 5v, correct? Will that be enough to work with?

Have any of you worked with this before?

Thanks,

-adam

So, something like this should cover me?

http://www.national.com/pf/DA/DAC0800.html

I found that by looking at Ken Stone's wavetable module schematic. I figure that has to be a decent example of generating CV.

http://www.cgs.synth.net/modules/wavetable.html

idx wrote on 25.01.2007 at 19:09:40:


With the resistor stage dac (i assume a simple "ladder" structure), are you limited to 0-5v of scaling or can you increase it to 15v with an outside power source, as with the Ken Stone example.

Are you using 4 i/o pins for your resistor ladder?

Hopefully that makes sense. I haven't messed with this stuff a whole lot over the past decade so I have some catching up to do.

Thanks for the link. I'll need to order some parts.

It appears the 8-Bit Descreet DAC Module 1 schem covers what I'm trying to accomplish. To get a higher voltage that the 5v I'd probably just apply a hotter voltage across P1, correct?

I finally found some time to mess with this last night.

I made an 8-bit R2R digital-to-analog converter. (I also tested with a DAC0800 chip)

Was sending control voltage to my modular synth using a simple loop where I spit out like 16 steps of binary data. I fed that into my exponential input to control the pitch of a VCO.

You can see a photo here of the pile of wires.

http://farm1.static.flickr.com/148/396515209_0ad58fb480_o.jpg

I plan to do some more work with this later. I didn't even need the opamp following the R2R. The voltage the Arduino generated was plenty enough to control pitch. I haven't tested it on a gate input yet, but I assume that should work, too. I would like to get the 741 working with it, though. From what I've read, it smooths out the signal quite a bit. I'd also like to pickup some 1% resistors to get more precise control.

This project really makes me realize how much I need an oscilliscope.

Nice one, and real nice looking modular, I take it your running all outputs direct from the arduino?

I did the naughty for the oscilloscope and sent it through a pre-amp before my computer btw, the signal was very low anyways, but it enabled me to run an oscilloscope app too get some rough idea what was going on.
I'm sure some people on here will caution me on this, as I'm sure I should be using some input buffer of some sorts

I'm trying to conserve ports on my arduino as to get midi input also, and possibly another serial in for some crude control input.
Running it through the hc595 causes a bit of spiking due to it not holding the signal I think, Im now experimenting with some gate- flip/flops to see if i can do sample-hold the signal before it goes through the R2R.

It would all be a lot easier for me using something like the DAC0800 like you mentioned, but it isn't half as much fun and messy as the R2R is it ?

Project is up here along with a polydac build if your interested.
http://homepage.mac.com/speedghost/JaffaMountain/page17/SynthDIY.html

Theres also an arduino page on there where I have a rough arduino pdf and omnigraffle stencil I use for mocking up some ideas.

I'm probably going to build the arduino into part of my modular as shown somewhere earlier in the blog. In theory once its running the polydac should be able to through midi to the arduino rack while the arduino outputs sound to the rest of the modular stages.  I'm hoping for lots of noise and character

You can take a look at my "Computer Interface" at the bottom of this page:
http://kymatica.com/index.php/Hardware/Schematics

I use it to control my homegrown modular through the paralellport.
My plan is to build a new one based on the arduino, so that I can controll it through USB instead.  
(parallellports are outdated nowadays...)

I don't like using midi2cv interfaces due to the limitations of MIDI (resolution and speed).

If you guys come up with some nice midi code, I'd love to get at it.


I think that would be the hard part. After you have midi note values (goes up to 128 or sommat), just spit out data to a DAC. I'd want my DAC to be more accurate than 8 bit though. The purpose of a control voltage is to allow as smooth a transition as possible. You might even want to build a glide circuit that smooths out the output...


Anyway, working backwards, you might want to get a control voltage (from a pot or something) and control your VSTi from it. Whatev.



Maybe soon VSTi will be bundled with hardware? (Ultimate copy protection is hardware)