DAC output

Feifer · Joined: May 16, 2012 Posts: 32 Location: San Diego

I was just wondering if anyone has ever tried to interface a Lunetta with an analog synth in this way. I know a common use is to use a Lunetta as a gate pattern generator, but does anyone have experience with taking some data streams from various spots and put them into a digital to analog converter to be used as a control voltage?
Edit:
I'm reading about R-2R resistor ladders, so I know that's always there, but I was thinking about a chip like a dac0830 (which I have left over from a failed midi to cv project).

JingleJoe · Posted: Fri Sep 28, 2012 6:49 am Post subject:

I thought DAC chips just had R2R ladders in them? Laughing

one of my earlier devices (the lunetta death pipes form outer space) used just that, some square wave LFOs going into an R2R ladder and then into a VCO, there were other controls between for level and waveform.

Feifer · Joined: May 16, 2012 Posts: 32 Location: San Diego

Hey JingleJoe. Yeah, I guess the chips do have R2R ladders in them, although I'm sure much higher precision. What I was thinking of though was that on the chips you can give it a reference voltage, where as with just the resistors your reference voltage is determined by your CMOS output. I was just thinking it might make it easier to tune it to land on 3rds, 5ths, octaves, etc.
How did your setup sound? Was it pretty much random pitches, or did it ever come out sounding somewhat musical?
Thanks

Psyingo · Joined: Jun 11, 2009 Posts: 242 Location: Canada

There are many different kinds of dac topologies, r2r is just one.

http://en.wikipedia.org/wiki/Digital-to-analog_converter#DAC_types

Feifer · Joined: May 16, 2012 Posts: 32 Location: San Diego

I might experiment with this a little bit. If I use that 8bit DAC chip I have and give it a Vref of 5.313V, the least significant bit would be 5.313V / 256 = 20.8mV. Which would make the 3rd bit = 83mV or a half step for a 1V/oct synth. Ignoring the lowest 2 bits and use it as a 6bit DAC, I could get these values:
000001 = half step
000010 = full step
000100 = major 3rd
000111 = perfect 5th
001100 = octave
011000 = 2 octaves

At least I think that's right.. Confused

I'll report back if and whenever I get a result.

Feifer · Joined: May 16, 2012 Posts: 32 Location: San Diego

Well I made a little proof of concept circuit and it's working pretty good. I just have a clock going into a CD4516 decade counter, those bits get tweaked a little with some nand gates and then go into the top 4 inputs of a 8bit DAC. The DAC is being fed a reference voltage such that the 5th bit puts out 83mV and is then doubled up from there. Seeing how I've done pretty much all analog stuff up to now and this is really my 2nd attempt at CMOS, I'm wondering why I held off for so long. This is opening up a whole new can of fun! Very Happy