🚀 go-pugleaf

I'm trying to build a circuit which outputs a continuous square wave
where the period can be varied from about 4 seconds to 60 seconds using
a variable resistor.  The catch is that no matter what the period is,
the "high" must be a contstant 3 seconds, i.e, a period of 10 seconds
would have a 7 second low and a 3 second high.

I tried using a 555, but I'm not too familiar with them, and I can only
set the ratio of high time to low time, rather than a specific high time
for any period.

The circuit should run at about 10-12 volts.

Any ideas?

Thanks in advance,
	Andrew.

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Andrew W Hamilton
hamilton@vax1.acs.udel.edu
hamilton@freezer.it.udel.edu