Alternative to MIDI-CV revisited

[gstopp at fibermux.com]

     Don - great idea on the 4-chip converter - have you tried it? How well 
     would the log discharge curve comply to an exponential power-of-2 type 
     curve? Is there a "warpage" factor that can be added?
     
     I like the "hybrid" idea, using a converter plus a PLL for fine 
     tuning.
     
     I forgot to mention that the PLL approach produces an audio output 
     (the PLL VCO) as well as a CV, which is kinda cool to mix in to the 
     controlled synth's external VCF input.
     
     Also there's that trick seen in an old Electronotes - the external 
     audio signal to be converted to CV is processed into a square wave 
     before the conversion, and this pulse train is passed through a FIFO 
     to delay it, so when the external signal goes away the converter still 
     has time to sample and hold the CV before it starts trying to convert 
     zero hertz and the CV drops to zero.
     
     Much unexplored territory here....
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: Alternative to MIDI-CV revisited
Author:  don at till.com at ccrelayout
Date:    5/9/96 5:29 PM
     
A way around this problem is to use a "blind" converter for a first 
approximation, and then add a PLL loop to tweak that voltage a bit. 
You get the best of all worlds.
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     .
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Soooo, on the first cycle one cap charges for a fixed amount of time 
then discharges for the rest of that cycle, and on the next cycle that 
cap's voltage is held and fed to the output.  Meanwhile the other cap 
is doing the alternate job, holding while the first cap is charging/ 
discharging, and vice-versa.
     .
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The whole thing can be implemented in four chips (one cmos schmitt 
trigger, one cmos dual flop, one cmos dual 1/4 mux, and an opamp) and 
some random Rs and Cs.