[sdiy] I2C DAC

[jays at aracnet.com]

There are a lot of things they can be used for. I work in instrumentation and here are some of the things we use them for:

Offset calibration - Add some offset voltage to a channel on an instrument to null out any internal offsets so 0V is really 0V.
Trigger thresholds - CMOS, TTL and a number of other signal/logic types all have different on/off thresholds.
Voltage refs - We use them as voltage references in power supplies to tweak the voltages. Also done on computers to over-clock.
LCDs - Brightness and backlight control.
***

Jay S.

Mike Beauchamp wrote:

> I don't mean to jump in on this thread, but can anyone show me an
> example of a 12-bit DAC  (I2C is fine) that is being used to output
> CV?
> 
> I guess I was always under the impression that DAC chips were only
> useful for audio applications (that is, constantly changing values)
> and I never thought they could actually just "hold" a value and do it
> with any stability, etc.
> 
> Mike
> 
> 
> 
> 
> On Sun, Jun 20, 2010 at 9:28 AM, Eric Brombaugh <ebrombaugh1 at cox.net> wrote:
> > On 06/19/2010 02:09 PM, MTG wrote:
> >>
> >> I'm almost out of pins, but I have two left in a project that I want to
> >> hook a DAC up to for control voltages. Anyone recommend a decent I2C
> >> single or multi-channel 0 to 5v voltage out DAC? What are most people
> >> using for resolution of control voltages these days? I know 7-bits was
> >> the standard for a long time. Is it worthwhile looking at higher
> >> resolution for things like filter cutoff or pitch bend or ... ?
> >
> > I think you'll have a hard time finding something as low as 7-bits
> > resolution. 8 is pretty common, but for CVs is a bit coarse. 12-bit
> > resolution will cover most CV applications without too much in the way of
> > zipper effects and can even be used for reasonably accurate 1V/Oct scaling.
> >
> > What processor are you using? Does it have a hardware I2C capability, or
> > will you have to bit-bang the low-level protocol? I2C can be a bit tricky
> > due to the built-in acknowledge cycle, and somewhat slow to update due to
> > the relatively low clock rates. On some MCUs the pins available for I2C
> > ports are limited due to the open-collector drivers required so you may not
> > be able to arbitrarily reassign them.
> >
> > Eric
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