[sdiy] Choosing a DAC

[George Hearn]

Maybe slightly off topic but if you are using PWM and a filter for a DAC, a
good trick if you want a nice bipolar output is to use the PWM pin as the
select input to a multiplexor (4052/4053 etc.).  The inputs to the
multiplexor can then be the supply rails or whatever range you want at the
output.  For example +/-5V on the multiplexor inputs would give a range from
-5V to +5V with 0V at 50% duty at the filtered output.  Where it gets really
interesting is that you can actually then feed other signals into the
multiplexor inputs, even potentially audio.  The multiplexor is a single
component and avoids an opamp with resistors etc.  Just an idea!  George 

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jerry Gray-Eskue
Sent: 29 June 2009 20:37
To: Synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Choosing a DAC

Good accuracy requires a long count period to adjust the duty cycle in. By
the time you add a filter ( and its time constants) to get a solid DC level
PWM is very slow compared to other DAC types. Depending on your PWM clock
speed and what you are using it for, it MAY be fast enough for satisfaction
performance.

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of David Anderson
Sent: Tuesday, July 07, 2009 12:12 PM
To: Synth DIY
Subject: Re: [sdiy] Choosing a DAC




Ingo Debus wrote:
> Can you use a PWM-based DAC? This would be very accurate, and since you
> only need 8 bits (or even less) it would surely be fast enough.
>
> I'm not an AVR guy, but many microcontrollers have some PWM output
> already on chip.

And here's an example of converting PWM output to a 0-10v range. There's
a circuit Melanie's reply:
http://www.picbasic.co.uk/forum/showthread.php?t=245

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