I am planning on interfacing the Daisy Seed with a MAX11300 chip to give me 20 DA (CV) outputs to control a bunch of Electrosmith analog submodules. I see there is support in libdaisy for the MAX11300 but does anyone have any examples of using the MAX11300 to provide control voltages for the Electrosmith analog submodules?
Why do you need so many DACs?
You can control dozens of oscillators with just one DAC.
The Profit 5 used one DAC to control 38 different CV channels. This was using a Trash 80 8 bit microcontroller and 1980’s multiplexers. Using the two DACs on the Seed+ plus a modern multiplexer you should be able to control MUCH more.
Is there a multiplexer chip that holds the values of channels when they are not selected?
Why would you need this? you can just store the value in code any time the multiplexer updates.
I’m talking about CV output here. I want the control voltages of the modules I’m controlling to remain stable after I’ve set them. If there is a mux between the DAC and the CV input to the module I need to make sure it retains its value.
Ah sorry, I was indeed thinking multiplexing for input 
I’m not aware of a chip that combines the mux with sample and hold. TI has an app note about how to build it:
DACx0501 Delivers Multichannel Output using External S&H for Battery Test Equipment and Oscilloscope_3pages_sbaa326.pdf (48.6 KB)
I didn’t know that either, makes sense that mux and S&H would be on a single IC, since they are so often used together.
“Is there a multiplexer chip that holds the values of channels when they are not selected?”
Holding the values is as simple as adding a capacitor (and often an opamp) after the mux, this is how the Prophet did it.
This website has detailed schematics and explanation of the Prophet Sequential Prophet 5 Rev 4 – Info and Modifications – maffez synth mods
Also seems worth pointing out that the MAX11300 only has one DAC. It has an onboard multiplexer as well.
Do I need to use capacitors on the output of the MAX11300 to hold the values? Do I need to cycle through all of the outputs and continually post values to keep them constant?
As @IC_Alchemy mentioned: you’ll need a Sample&Hold (which is basically the functionality you are asking).
However I’m not sure how you could sync those up with the output selection.
And anyway having to add an S&H to every output would make the circuit blow up quite a bit …
Maybe I should step back and ask if there is a book or series of web articles that would help me get up to speed on synth circuits. I’m a programmer and have some experience with electronics but I haven’t done analog design yet. I bought a bunch of the ElectroSmith analog submodules hoping I could just wire them together and to a microcontroller via something like the MAX11300 and create a synth that could be controlled by the microcontroller but have an analog signal path.
No, but you probably do have to read the data sheet, and probably should get a chip and start experimenting.
EDIT: a little more reading of datasheet and I’m less certain about how to set a steady voltage on a port.
I have the PIXI Click module that contains a MAX11300 so I will be experimenting with it soon. I have looked over the data sheet but I need to go over it more closely. Thanks for your help!