FW: [sdiy] DAC via Mux

[Jerry Gray-Eskue]

-----Original Message-----
From: Jerry Gray-Eskue [mailto:jerryge at cableone.net]
Sent: Thursday, November 19, 2009 9:06 AM
To: Justin Owen
Subject: RE: [sdiy] DAC via Mux



It sounds like you are on a good path except I suspect you need to put a
Sample Hold on each mux output.
This setup is like that used in the Fatman from PAIA.

Take a look at this Figure 5a at the bottom right of the schematic to see a
possible Sample Hold setup using a TL084 and a .1 cap.

Without a Sample Hold you are going to get a lot of uncontrolled voltage
output. The speed you use clocking the mux with S/H should be no faster than
the time the S/H takes to acquire a good match for the input
voltage,(several Time Constants of the Mux ON resistance and the Cap used)
and the time between updates should be short enough that the S/H do not have
time to drift significantly.

- Jerry

http://www.paia.com/manuals/docs/9308-fatman-manual.pdf


- Jerry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Justin Owen
Sent: Thursday, November 19, 2009 6:08 AM
To: SDIY List
Subject: [sdiy] DAC via Mux


Hey all,

I want to run the 2 outputs of my TLV5618 dual DAC via a 4052 2 x 4 out Mux
but I thought I'd check in here first just to make sure I'm not heading off
on completely the wrong path.

Firstly - my plan is to clock the mux via pins on my micro. The sequence
would be - inhibit the mux, set the DAC output value then open the correct
mux output - and then just keep repeating that. I figured a clean break as
the mux was inhibited is better than glitches and crap as the values were
re-written. Sound right?

Secondly - I'm wondering about the speed I should be clocking the mux at and
if I should be trying to 'sync' that to the write rate of the DAC. As fast
as possible? Something based on the speed of something else?

Lastly - I'd appreciate any advice on signal conditioning into or out of the
DAC.

The DAC will be outputting various types of CV - i.e. Pitch, Velocity,
Envelopes, etc.

Any input would be appreciated.

Cheers - J.


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