[Lf] DDS controlled via soundcard

[Andre Kesteloot]

DL4YHF at aol.com wrote:

> Hi all,
>
> During a nice QSO in Jason mode today, and thinking about this and
> that, a crazy idea went through my brain. Maybe it's only good for the
> waste bin but how about this:
>
> Let the PC produce a digital control word for a DDS  VIA THE SOUNDCARD
> ?
>
> A DDS like the AD9832 needs a special serial control word, which is
> generated by a PIC processor in most cases. Three digital lines are
> required. How about "producing" the control word for the DDS via the
> SOUNDCARD ? We could either use a stereo output for clock+data
> (producing digital signals) , a few clamping diodes, two or three
> transistors and possibly a monoflop for the FSYNC signal (a third
> control line from PC to PIC). An alternative would be using different
> levels for the FSYNC, but proper level adjustment and clamping would
> be required because most audio outputs are only "AC coupled".
>
> Johan (SM6LKM) has written a routine in "C" for PIC controllers which
> I have adapted to run under DOS, using the parallel port. But it's
> complicated to do this under windoze, especially if the DDS shall be
> controlled in a highly "synchronous" way through the parallel port.
>
>
> What would be the benefit of using the soundcard to drive a DDS ?
> - you wouldn't need a programmed PIC processor acting as an interface
> between PC and DDS.
> - you wouldn't need a LPT interface which is tricky to access under
> Windoze NT + XP.
> - you wouldn't need a serial interface which does not exist on some
> cheap notebooks.
> - no need to fool around with USB programming
> - The serial control word for the DDS chip can be timed very precisely
> under windoze. A
> continuous output (with update the DDS every 100 ms or so) is
> possible.
>
>
> Disadvantages:
> - It's not a 'stand-alone' solution. A PC (or at least one of these
> tiny PDA's) is always needed. But which of the "modern modes" runs
> without a PC ?
> - To implement this, basic knowledge of Windoze API programming is
> required. But I know at least one other reader of this reflector who
> has.. ;-)
>
>
> If this sounds interesting, let me know and I'll do some more
> "research". The result could be a routine which produces raw 16-bit
> analogue samples to drive an AD9832 (which is the only DDS I have at
> the moment).
>
> 73,
>  Wolf DL4YHF.



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