Re: Circuit Power Consumption



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No. A 555 is a very bad choice for such a long timeout. However,
the second one could be used to drive a piezo buzzer.
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(and)

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No. There is no need for a voltage divider since CMOS is available
which can run directly off of 9V at _very_ low current.

Ahh ok. is the "755" and "CMOS 555 Timer" the same thing? Jameco's
'search' function was giving me the same results for both searches, but
IMHO it's not the greatest at times.

I'd use something like a 4060 for the timer and a transistor to turn
on a 555 astable to drive the piezo buzzer.

Good thing I asked. I had never heard of a CD4060 before ;) Does "CD"
mean 'CMOS' or something?

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4) This circuit will be exposed to outdoor temperature changes. Will
that make a very large impact on its timing intervals?

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depends on what's being used to generate the timer's clock. What
kind of stability do you need?
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It's pretty non-critical. The long 'wait' period could vary by a
couple of hours, actually. I would prefer it to err on the side of
longer, but either direction is ok. I bet that any variation would be
in *minutes* at the most, huh?

However, when you say "what's being used to generate the timer's
clock", do you mean 'which IC'? I'm assuming that the 4060 can be set
up to just 'run' automatically once you apply power to it, like the 555
and things, right? No need for an external clock or trigger.



5) Any estimate as what to expect for battery life? I realize that a
precise answer is hard, but am I looking at hours, days, weeks or
months, perhaps?

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Neglecting the buzzer for a moment, if the rest of the circuit draws
500 microamps from the battery, all the time, and the battery has a
capacity of 500mAH, that means you can expect about 1000 hours out
of the battery. About 6 weeks.

If the buzzer needs 50mA and it runs for 15 seconds a day, that's
only increasing the load on the battery by about 9 microamps, so the
life would still be about 6 weeks. The trick here would be to get
the timer to run on as little current as possible. I think 100
microamps is doable and that would get the life up to about 10000
hours. About 417 days.


Thanks for this rundown on the time, or *specifically* how you deduced
it. It's given me more stuff to google ;-) 260 days is entirely
acceptable. The plan is to build several of these circuits with
slightly varying 'wait' periods, and tape each one to a 9V battery.
Then I'll randomly stash them out in my best friend's workshop and see
how long it takes to annoy the bejeebus out of him >:-) I'll pretend
like I don't hear them or something. After awhile I'll stick one under
the seat of his truck and one under the lid of his toilet or something.

(We prank each other all the time, it's all great fun.)

Thanks for all the suggestions and help.

Jasper:
If i were to use a uC then I'd have to make it play music or something.
You know, "The Atmel Tiny Canon in Dbminor" or something :-)
I'm already trying hard enough to resist using multiple buzzers and
multiple 555s to play reciprocating tritones or something. :-D

--
John Fields
Professional Circuit Designer

-Phaeton,
Stark Raving Mad Scientist

.

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