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From: "John Jardine"
Subject: Re: job: Who can draw or send me a 1/10 second countdown timer?
Date: Fri, 6 Dec 2002 15:30:52 -0000
References: <3DF0D25D.C182E284@rica.net> <3YJYg5Bfv679EwTE@jmwa.demon.co.uk>
NNTP-Posting-Date: 6 Dec 2002 15:18:38 GMT
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John Woodgate wrote in message
> I read in sci.electronics.design that John Jardine
> wrote (in
> ) about 'job: Who can draw or send me a 1/10 second countdown timer?',
> on Thu, 5 Dec 2002:
> >Years ago did a photo timer 0 to 99 secs using a single pot. The dial was
> >logarithmic which allowed 0.1 sec increments at the bottom end and
> >(or less) at the top end. Time setting resolution depends how you mark
> >dial and how big you make it.
> And the law of the pot. Log law pots (if that's how you obtained the log
> scale) have just two or three linear sections of different resistivity.
> Regards, John Woodgate, OOO - Own Opinions Only.
> Interested in professional sound reinforcement and distribution? Then go
> PLEASE do NOT copy news posts to me by E-MAIL!
A perfectly normal linear pot. It's the distributed CR network that acts
with a log time constant. More sections more log ranging (or design for
other curves). Acts in a similar manner to say a segmented approximation to
a 1db or 3db per octave audio noise filter. . Each CR section TC is about
20X the preceding one (best least squares approximation to a log conformity
curve). Vast frequency ranges can be covered with no range switching.
Idea came from a reference in Scroggie's R.E.L.H. (looked, can't find ref).
Original article was about 1949 as a "Six league oscillator". Sine wave,
dual ganged pot, two identical distributed RC 90deg phase shift networks.
(lost that as well!)
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