Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!mephisto!udel!udccvax1!hamilton
From: hamilton@vax1.acs.udel.EDU (Andrew W Hamilton)
Newsgroups: sci.electronics
Subject: Help with a timing circuit
Message-ID: <5712@udccvax1.acs.udel.EDU>
Date: 12 Feb 90 23:33:38 GMT
Reply-To: hamilton@vax1.acs.udel.EDU (Andrew W Hamilton)
Organization: University of Delaware
Lines: 21

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