[sdiy] PLL / VCO

[Scott Gravenhorst]

You can see my PLL stuff at:
http://home1.gte.net/res0658s/fatman/4046pll.html


harrybissell <harrybissell at prodigy.net> wrote:
>Andrew Wyld wrote:
>Hi there,
>
>I am wondering if it is possible to use an arbitrarily weird VCO in a
>PLL.
>Basically I want to use a square wave from a computer (specifically a
>horribly cannibalized Commodore 64) to drive an analogue VCO, making a
>drift-free synth that can be sequenced and controlled completely from
>the
>computer console, but still sounds like an analogue synth.
>
>I'm figuring I can do this if I do some kind of horrible gating
>operation on
>the VCO.  What would people suggest I read up on / look up on the net /
>etc?
>
>Of course its possible.  An arbitrary VCO needs to have an acceptable
>range, and some
>waveform that will be stable... specifially a square wave output.  You
>need to feed this
>to a phase discriminator, and filter the output and send it to the VCO.
>
>If your 'arbitrary' VCO does not have a square wave out, you'll need to
>make one.
>The toughest challenge will porobably be the loop filter...which will
>set the speed that
>the loop can lock at. Too slow and you will have a permanent glide..too
>fast and it will
>bounce and overshoot.  Just right might not even be 'just right'...it
>depends on how
>fast you plan on running that sequencer.
>
>Check the data sheet for the CD4046 which should get you started. Also
>look up
>Scott "Fatman" Gravenhorst of this list... who has used the CD4046 a lot
>in his
>PAiA Fatman modifications.
>
>H^) harry
>
>
>
>
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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