ComputerVoltageSources

Greetings group!

I'm glad to see this kicked off. I was watching with
interest the discussion in synth-diy a few weeks back
and wanted to pursue this area further.

One thing that caught my eye in the earlier discussion
was the idea of using a fast CPU as not only a CV
source, but also for VCOs, VCFs, VCAs, and general
signal processing. The BasicATOM Pro isn't quit fast
enough to do a lot of this, but several other
processors were mentioned that would support this.

I followed up on the Analog Devices ADuC702x family
which looks very promising for this. It's a 40MHz ARM7
with 12-bit ADC (muxed) and 4 dedicated 12-bit DACs
on-chip. Some members of the family are inexpensive
(~$6) and available in packages that are relatively
DIY-friendly.

I'm presently doing top level design on a 4chl
input/4chl output module based on the ADuC7020. This
member of the family has somewhat limited digital I/O,
but with an SPI-based port extender such as the Maxim
MAX6957 it would be possible to support buttons, LEDs
and an LCD display.

ADI sells a $30 development system for this part which
includes the ADuC7020 on a 40-pin DIP carrier, along
with a download cable and two different C-based IDEs.
I've ordered one of these and plan to slap something
together.

Back-of-the-envelope estimates indicate that it should
be possible to get ~60kHz sample rates on 4
simultaneous channels, including a bit of oversampling
& filtering on the ADC inputs to eliminate noise and
improve SNR.

The big downside is that the development environment
is not BASIC but C. I'm comfortable in C, but I agree
with Grant's earlier observation that BASIC is a great
enabler, allowing a broad range of users to quickly
come up to speed and contribute. There is the
possibility of porting a freely-available BASIC
interpreter such as Brandy-BASIC to the ARM7 though,
and this is on my road map.

I'd be interested in any comments & criticism from the
group.

Eric


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