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<DIV><FONT face=Arial size=2>What you have here is almost a classic LFO
design.</FONT></DIV>
<DIV><FONT face=Arial size=2>Just replace R1 with a potentiometer to make the
frequency variable.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Probably one of the easiest ways to ad CV control
is to replace R1 with a LDR </FONT></DIV>
<DIV><FONT face=Arial size=2>Put a resistor parallel to the LDR to set the
lowest frequency.</FONT></DIV>
<DIV><FONT face=Arial size=2>Have a LED light the LDR and your almost
done.</FONT></DIV>
<DIV><FONT face=Arial size=2>There are plenty examples for how to control the
LED with a opamp on the net.</FONT></DIV>
<DIV><FONT face=Arial size=2>BTW you need to cover the LED/LDR combination in
complete darkness.</FONT></DIV>
<DIV><FONT face=Arial size=2>Ready made combinations are also available and
known as Vactrols.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>An other option is to replace R1 with a 4053 Cmos
switch and a series resistor to set the highest frequency.</FONT></DIV>
<DIV><FONT face=Arial size=2>This would work like this.</FONT></DIV>
<DIV><FONT face=Arial size=2>- The comparator sets the switch
position.</FONT></DIV>
<DIV><FONT face=Arial size=2>- The switch toggles between the </FONT><FONT
face=Arial size=2>CV and the inverse of the CV.</FONT><FONT face=Arial
size=2> </FONT></DIV>
<DIV><FONT face=Arial size=2>- The CV or inverse CV load/unload the
integrator.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Both options work ok for a LFO or other application
where frequency and temperature stability is not critical.</FONT></DIV>
<DIV><FONT face=Arial size=2>However neither will be the best solution for
music VCO.</FONT><FONT face=Arial size=2></FONT></DIV>
<DIV><FONT face=Arial size=2>It might be a idea to take a look at VCO examples
on the web.</FONT></DIV>
<DIV><FONT face=Arial size=2>You will see VCOs generally use a slightly
different setup,</FONT></DIV>
<DIV><FONT face=Arial size=2>resulting in more simple and reliable
solutions.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>HTH</FONT></DIV>
<DIV><FONT face=Arial size=2>Theo</FONT></DIV>
<DIV> </DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A href="mailto:housenationmedia@yahoo.com"
title=housenationmedia@yahoo.com>bill berzinskas</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
href="mailto:synth-diy@dropmix.xs4all.nl"
title=synth-diy@dropmix.xs4all.nl>synth-diy@dropmix.xs4all.nl</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, October 19, 2002 7:34
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [sdiy] How To Make This
Oscillator into a VCO</DIV>
<DIV><BR></DIV>
<P>Hey everyone.. </P>
<P>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? </P>
<P>you can see the schematic here: <A
href="http://hnrserver.dynip.com/oscschem.jpg">http://hnrserver.dynip.com/oscschem.jpg</A></P>
<P>Any help is appreciated! </P>
<P>--billie</P>
<P><BR>
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