Subject: Re: One-Shot
Date: Sat, 14 Dec 2002 14:46:38 -0800
X-Mailer: Mozilla 4.78 [en] (Win98; U)
Anyone have a circuit for a one-shot that would
light up a LED for a exact
period of time after a button is pushed, no matter
how many times the button
is pushed. All the timers I have found are
cumulative, and keep resetting
the timer every time the button is pushed.
Specification Police Alert!!!
Yet another vague question. In the general case,
what you stated probably
cannot be done. With a tiny amount of
specificity, it's probably trivial.
Last thing you need is a circuit that doesn't do
what you want.
A circuit suitable for lighting the led for 10 uS
might be different from
one that lights the led for a week.
Are you saying that I can push then release the
button randomly for a month
and you want only one lighting of the led? What
defines the end of the pushing session
so the circuit can reset? Whether you're cycling
the button or just holding it on
could simplify the solution.
What is exact? Ain't no such thing in
electronics. How long and how accurately matters.
Any restrictions on the button? Can I define the
You gotta put some boundaries somewhere on
Once you've adequately stated the problem, you'll
probably find that the problem
is a LOT more complicated than you thought. If
it's not obvious from your
complete spec, post the spec and ask again.
Specify a state machine. Although it may
degenerate into some analog timers if your
requirements are loose enough.
For these kinds of stuffs, a PIC or similar
processor is often a good
solution. Cheap, simple, ultimately
configurable...once you get past the
learning curve. If you don't need portability or a
lot of them, stuff the
switch into the parallel port on a PC and do it in
BASIC. Emulate the led
on the CRT. Don't get more simpler than that.
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