an idea ...

[Kimmo Koli]

On Wed, 13 Nov 1996 Christopher_List at Sonymusic.Com wrote:
> ...
>   There's a lot to work out - such as the classic program-able synth
>   dilemma - "how do we show knobs with values that differ from the
>   programmer's values?"
> 
>   I've always thought the best solution is having an LED next to each knob
>   that lights up when a knob differs from the program. It would also be
>   need to have a LED/LCD to display the current program number.
> ... 

Why not toggle with a push button between the memory CV and the knob CV. If
done with CMOS-switches and logic, you could reset the toggle switch every
time a patch is recalled from memory.

Or make a derivate of the knob voltage to switch the control from patch 
memory to the turned knob. And then show with a red/green LED when knob 
position matches with the patch memory...

And another thing:
Why use D/A-converters for CV-control ? A 100 kHz variable pulse-width signal
(or even better a tri-state signal = double resolution) could be easily 
generated with software. A microprosessor would update 8 of these at the 
same time with one parallel port and 8 RC low-pass filters. Should be 
quite clean DC for controlling VCOs and VCFs. The settling time and 
resolution can be adjusted by the RC time constant independently for each 
CV-output. An for lower noise these bit-streams could be opto-coupled. 
Or make differential outputs...

Higher rate bit-steams coud be implemented with 8-bit counters etc.

That's all,
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   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      Otakaari 5 A 
   Tel:  +358 9 451 2273              FIN-02150 Espoo
   Fax:  +358 9 451 2269              Finland 
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