[sdiy] "voltage control" on the 556

[Scott Gravenhorst]

>On 8 Mar 2009, at 05:04, Horton wrote:
>
> I was wondering if there's any way to take advantage of the "control
> voltage" pins on the 556...
> Am I totally barking up the wrong tree with this one, or what?

It works by varying the threshhold voltage at which the timer will reset.  As such,
it will control the pitch of an astable multivibrator, but within a limited range
and it will also change the output amplitude (lower amplitudes for higher frequencies).

A way to get better control over the pitch of a 555 oscillator is to use a circuit
like the PAiA FatMan VCO.

Also, the CMOS version (7555) which is pinout identical is a better IC because it
won't spit nasty current spikes at your power supply every time it resets.

-- ScottG
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-- Scott Gravenhorst
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