Alternative to MIDI-CV

Kimmo Koli kimmo at clara.hut.fi
Thu Feb 8 17:02:42 CET 1996


william.b.fox wrote:
> 
> Hi Kimmo,
> 
> Thanks for the Frequency-to-CV schematic.  I have two questions.
> 1.  What value resistor should be used?
> 2.  What is connected at the top of that resistor? (5V, 15V?)
> 
> Bill Fox        wbf at aloft.att.com

Actually, that schematic was only a principle to input a exponential CV
to a
VCF or a VCO that has linear CV control and uses the typical exponential
converter.

The Frequency-to-CV converter can be built for example from a LM2907 or
LM2917.
Or simply by chaining these blocks:

   comparator       pulse generator       filter
      or        ->     for ex. 555   ->  10-100Hz
  zero-cross det.                        low pass
     
If the zero-cross detector triggers both at rising and falling edges,
input frequency is doubled and ripple is reduced.

If the pulse generator uses accurate pulses (Xtal-clock synchronous)
and the amplitude is accurate, accurate F-to-V conversion should be
possible.

If the input frequency is high enough, also the filter corner frequency
can be higher and the response time is faster. Otherwise filter should
be 12 db/oct or even steeper.

Hope this helps,
--------------------------------------------------------------------------------
  Kimmo Koli      			     Email: kimmo at clara.hut.fi 
  Helsinki University of Technology          URL:
http://clara.hut.fi/~kimmo
  Electronic Circuit Design Laboratory
  Otakaari 5 A 
  FIN-02150 Espoo     			     Tel:  +358 0 451 2273
  Finland      				     Fax:  +358 0 451 2269
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