Re: How to count pulses per second ?

In article <pan.2007.02.13.23.58.32.761612@xxxxxxxxxxx>,
Rich Grise <rich@xxxxxxxxxxx> wrote:
On Tue, 13 Feb 2007 14:58:15 -0800, Mike C wrote:
On Feb 13, 5:41 pm, "Tim Williams" <tmoran...@xxxxxxxxxxx> wrote:
If it's constant, missing pulse detector. Can be made from a few
transistors, or a few transistors and a comparator, or a single chip
(LMxxx?) that does it. Hell, it can be done with the 555, IIRC.

If it's not constant, then a decade divider like CD4017 set to reset every
second (so you need another clock) and something to say that it's got enough
counts or it doesn't.

"Mike C" <tiberi...@xxxxxxxxx> wrote in message

Hi, I'm hoping someone could help me create a very basic circuit which
would:

Count the number of pulses it receives per second (from a 555 timer,
or a switch, for example) and if the number of pulses per second is
equal to, or greater than 10 it turns on a transistor.

So basically it should check every second if a clock frequency of 10Hz
is being met - if so, a transistor should turn an LED on and keep it
on for as long as 10Hz a second is hitting the circuit. As soon as the
clock stops, or the frequency goes below 10Hz, it should turn off the
LED.

Thanks so much for your help !

Guys, thanks alot for your response. In this case, the clock
frequency is variable, so it would just need to count the number of
cycles per second, and a missing pulse detector may not do it. I can
see how a decade divider could work (I just dont have any lying around
now, and would like to build it this week). What did you have in mind
by doing it w/ just transistors and a 555 ... or a comparator .. im
looking for anything crude and simple. :)


The dead simplest would be an RC low-pass or high-pass, and a comparator.

You'll have hysteresis, if you don't want your comparator oscillating,
and it won't respond very quickly, but it'll demonstrate the concept.

LM339's come 4 to a package. You could make a one shot action by having
one discharge a capacitor and another monitoring the voltage on it. This
way, the first comparitor oscillating won't show at the output.


--
--
kensmith@xxxxxxxxx forging knowledge

.

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