From: Spehro Pefhany
Subject: Re: blinking LED
X-Newsreader: Forte Agent 1.92/32.572
Date: Tue, 12 Nov 2002 19:56:17 GMT
NNTP-Posting-Date: Tue, 12 Nov 2002 14:56:17 EST
On Tue, 12 Nov 2002 19:03:52 GMT, the renowned "Michael Painter"
>I know little about design.
>I want a LED to blink at a steady rate, once every 15 seconds and it should
>be accurate within a second or so.
>An on/off switch and in a small package wearable on a wrist would be ideal.
>It would be used to take (human) pulses in low light, no light, or sometimes
Pretty easy. You're only asking for 5%-ish accuracy. A 555 would do it
if you don't mind calibrating it (adjusting a trimpot to get the 15
seconds accurate). Use a CMOS type (eg. TLC555) for battery
operation. This would be about 6 or 8 parts total, including the
adjustment potentiometer, and could be fairly small (the film type
timing cap would be the largest component, followed by the trimpot)
There are some microcontrollers that could be programmed to do it with
essentially no external parts (a capacitor and a resistor). With the
addition of a few more parts (a watch crystal and some passives) it
could be made as accurate as you'd ever want, or to have features such
as a switch stepping through 15/30/60 seconds pulses.
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