[sdiy] 12 bits D/A converter?

[Eric Brombaugh]

Miguel,

I checked out your schematic and it looks like a cool little synth. I 
see that you're using a dsPIC30, and that your current DAC is a 
home-made R2R ladder driven from two registers loaded separately in 
parallel.

I can see why you're interested in a monolithic 12-bit DAC - the ladder 
DAC takes a lot of parts and suffers from some interesting distortion as 
you load the two halves sequentially.

In addition to the DACs that Tony mentioned, have you considered a SPI 
(serial load) DAC? You can get them fairly cheap from many sources (ADI, 
Linear Tech, TI, Microchip, etc) and your dsPIC30F3014 has a built-in 
SPI port that would be able to drive it. I initially used a 12-bit SPI 
DAC from Microchip in some of the early prototypes of a voltage 
controlled digital oscillator that I did last year and they were easy to 
use as well as inexpensive. If you try the Microchip parts you can get 
free samples from them too.

The only downside is that I don't know what your sample rate is. If 
you're running faster than about 200kHz it may be difficult to run the 
SPI port fast enough to keep up. At lower rates though they work nicely.

Eric

labolida wrote:
> Thanks Tony, i'll looking for in local market (Brazil, Rio de Janeiro)
> but i'm afraid that it will be veri expensive here.
> Cheers 
> ---------- Cabeçalho original -----------
> 
> De: synth-diy-bounces at dropmix.xs4all.nl
> Para: "Synth DIY" synth-diy at dropmix.xs4all.nl
> Cópia: 
> Data: Thu, 12 Jul 2007 14:31:43 +0100
> Assunto: Re: [sdiy] 12 bits D/A converter?
> 
>> The AD7545 and the AD7945 are good products. Parallel load and 
>> multiplying so very good for DIY stuff.
>>
>> A bit expensive at about 8GBP each but samples would be available I 
>> would think.