From: John Popelish
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Subject: Re: job: Who can draw or send me a 1/10 second countdown timer?
Date: Thu, 05 Dec 2002 16:36:34 GMT
NNTP-Posting-Date: Thu, 05 Dec 2002 11:36:34 EST
> I'm looking for a photographic timer electronic circuit that lights a
> 100w/230VAC halogeen lamp.
> I could pay you with paypal.com or bank-deposit.
> *Timer 0 to 99 seconds or more
> *in 1/10 of a second
> *countdowntime saved for continues repeading lightings
> *with 3 or more 7-segment leds
> *10-digets keyboard OR 4 buttons(1/10sec+seconds up and down) OR 2
> buttons(faster counting by time pressed)
> *2 buttons start, stop/reset
> *Enough power for relay with 230vac/100w contact (halogeen lamp)
> Please let me know on: michelradino (a) hotmail . com ;-)
A bit of advice:
While you may need tenth second resolution when the total time is a
second or two, this digit is just a nuisance when the time is in tens
of seconds or more. So, if you build a timer with a 10 second dial, a
second dial and a tenth second dial, you have way more choices than
you probably need. If the selection were done with an up/down pair of
switches, and the time read out on a digital display, you could use a
program in a microprocessor to give you time steps that had a constant
ratio, from one step to the next. For instance, your camera does not
provide tenth of F stops, but selected constant ratio effective
exposure values at two to 1 ratios or square root of two to 1.
You might want the enlarger timer to have steps at the 4th root of two
ratio, so that every 4 steps would double the total time. It could
also round off the time to simple numbers, if the remainder were and
insignificant (much less than an adjacent step). The ratio might also
well be coarser for very short times, since the filament warm up time
(and especially the cool down time) gets involved in the effective
time, so very small steps are not very precise, anyway, without a
.1, .14, .2, .28, .4, .56, .8
1, 1.4, 2, 2.8, 4, 5.6, 8
These step by the square root of two, with a smaller jump at the digit
10, 12, 14, 17, 2, 2.4, 2.8, 3.4, 4, 4.8, 5.7, 6.7, 8, 9.5
4th root of 2 (quarter stop) steps. This decade could also be used for
tens of seconds and hundreds of seconds.
This sequence breaks the .1 second to 95 second range into only 42
choices, but would require a efficiently micro to hold the table of
times and operate the display.