[sdiy] How To Make This Oscillator into a VCO

[Theo]

What you have here is almost a classic LFO design.
Just replace R1 with a potentiometer to make the frequency variable.

Probably one of the easiest ways to ad CV control is to replace R1 with a LDR 
Put a resistor parallel to the LDR to set the lowest frequency.
Have a LED light the LDR and your almost done.
There are plenty examples for how to control the LED with a opamp on the net.
BTW you need to cover the LED/LDR combination in complete darkness.
Ready made combinations are also available and known as Vactrols.

An other option is to replace R1 with a 4053 Cmos switch and a series resistor to set the highest frequency.
This would work like this.
- The comparator sets the switch position.
- The switch toggles between the CV and the inverse of the CV. 
- The CV or inverse CV load/unload the integrator.

Both options work ok for a LFO or other application where frequency and temperature stability is not critical.
However neither will be the best solution for music VCO.
It might be a idea to take a look at VCO examples on the web.
You will see VCOs generally use a slightly different setup,
resulting in more simple and reliable solutions.

HTH
Theo

  ----- Original Message ----- 
  From: bill berzinskas 
  To: synth-diy at dropmix.xs4all.nl 
  Sent: Saturday, October 19, 2002 7:34 PM
  Subject: [sdiy] How To Make This Oscillator into a VCO


  Hey everyone.. 

  A week or so ago, I put out my schematic for an oscillator I was working on..  I got some good responses, and I've designed this 2 opamp oscillator (schmitt trigger and integrator)..  My question now, is how would i go about making this into a vco? 

  you can see the schematic here:  http://hnrserver.dynip.com/oscschem.jpg

  Any help is appreciated! 

  --billie





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