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Cheap 12 bit DAC and ADC's

Discussion in 'Electronic Design' started by Martin Riddle, Jul 18, 2009.

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  1. I'm looking for a cheap 5v Rail buffered output 12bit DAC
    And a 12bit ADC (8 channel).

    Any recommendations?

    Cheers
     
  2. John Larkin

    John Larkin Guest

    For the ADC, maybe an ADS7866 and an HC4051?

    John
     
  3. Joerg

    Joerg Guest

    Define "cheap". Also, none of them truly goes to the rail if that's what
    you want. Many are 0V to 4.095V because that gives you a nice 1mV
    granularity. Others go by whatever external ref you provide.
     
  4. Frank Buss

    Frank Buss Guest

    Depends on your requirements. There are huge price differences depending on
    speed. And there are different interfaces, like SPI or parallel and you
    might not like BGA style parts.

    A good source for selecting the right part is the parametric search at
    Digikey, even if you don't buy it there:

    ADC:
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556291

    DAC:
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556292

    Not cheap, but nice and fast is the LTC2624, which is on the Spartan3E
    evaluation kit, with which I've implemented my signal generator:

    http://www.frank-buss.de/SignalGenerator/
     
  5. Joerg

    Joerg Guest

    I like the AD5328 and the AD7928 but they aren't exactly cheap.
     
  6. I should have mentioned SPI, But I think the AD7927 is the one, half
    the cost of the LT part we are using now.
    The are some Dacs that are priced right from analog too.

    If I had extra port pins then the Mux I would play around with, but
    thats not an option.

    Thanks
     
  7. Joerg

    Joerg Guest


    That falls under "cheap"? Hmm, you guys leave too much money on the
    table :)

    At that cost I'd consider muxing the SPI stream so you can hang a
    register onto the SPI that rotates through the ADC channels. Not an
    option for the DACs though.
     
  8. Frank Buss

    Frank Buss Guest

    There are some cheap high quality audio DACs, but I don't know if they can
    go down to DC.
     
  9. Joerg

    Joerg Guest

    They used to, but at least the ADC part of audio codecs often has
    inherent highpass filtering in there which can't be turned off. Learned
    it the hard way when I wanted to hack a laptop into going down to below
    1Hz. But it did go down to about 5Hz.

    Also you usually get only two channels. Example of a really cheap audio
    DAC, for 3.3V supply though:
    http://www.nxp.com/acrobat_download/datasheets/UDA1334TS_2.pdf

    They don't even spec the offset of the opamp that does the current to
    voltage conversion. It could very well be above the 12bit granularity
    because it doesn't matter to the audio guys.
     
  10. Frank Buss

    Frank Buss Guest

    Sometimes it matters. If you have a sample rate change and you have to
    disable the output before changing the clock for the DAC to avoid any
    clicking noise, it could be a problem. I know a schematic with lots of
    transistors, op-amps and a relay, for which I've designed and implemented a
    software concept (including FPGA functions), which is really necessary to
    avoid any clicking noise for professional audio monitoring systems, where
    you can get deaf at signal levels of 0 dBu. I don't care, but looks like
    radio broadcasting customers do :)
     
  11. Joerg

    Joerg Guest

    True, don't ever touch the clock rate or data stream, then it is indeed
    a problem. Curing that at the output is like a squelch and it seems that
    even manufacturers of professional communications gear no longer fully
    understand how to handle this. As evidenced by the popping squelch and
    the schematic a guy at the German NG posted a while ago (Michael, the
    one with the large model railroad). That was a truly horrid circuitry.

    BTW, after we had our "glorious" switch to DTV (don't even get me
    started on this #@^&!! ...) we now "enjoy" the occasional tsk, pop, pock
    and phsst sound when video content such as news reporter pieces changes.
    Oh, and the movie we wanted to watch yesterday pixelated out into a blue
    screen, as usual.
     
  12. Well I could add like a 74HC595 and feed the mux with that. I think I
    have 1 or 2 pare port pins.

    Also For the DAC I found a microchip part MCP4922, $3.

    Cheers
     
  13. E

    E Guest

    Microchip? hmm..
    For the ADC maybe a dsPic with simple program to output data via SPI, $3
    Some devices have inbuild 16-bit DAC also (like dsPIC33FJ64GP802)
     
  14. Joerg

    Joerg Guest

    Well, there's the solution. All you need is to disassert the device
    select for the DACs/ADCs and run another CS line to the 595, then use
    the regular (same) SPI lines for clock and data.

    But that's only a dual DAC. Plenty of those.
     
  15. Joerg

    Joerg Guest


    Not really, each circuit situation is just too different and sometimes
    tricks need to be played with the DACs. I like the AD5328 and the AD7928
    for ADC when I have to have lots of channels (if I need more than one
    channel it's usually lots of them). For a 2ch DAC the DAC7612 is kind of
    ok at $3, although a long hard search should turn up less expensive
    ones. Whenever I have a project I go by price and most of all widespread
    availability. Certain parts are on the black list, but we all know who's
    those are.

    Most of the time my clients already have DACs or ADCs in their designs
    and prefer that I use the same.
     
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