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Subject: Re: Thanks!
Date: Sun, 17 Nov 2002 23:29:45 GMT
NNTP-Posting-Date: Sun, 17 Nov 2002 18:29:45 EST
Organization: Road Runner
> That's a great idea, using the unused part of the opamp as a flasher. Would
> you have a schematic for such a flasher????
> Thanks again
It's a simple thing, really. Here's a quick sample:
.1uf | ,---------. |
-V o---||----x-|- | | 10K LED
R1 100K | out|--x----/\/\----(>|---o -V
ENABLE o--/\/\--x--|+ | |
R2 68K | `---------` |
Depending on the op-amp, the ratio of R1 and R2 can vary slightly.
Generally, you can make them the same, but the duty cycle may not be
quite what you want. For a typical LM358, I usually use a ratio of
10/6.8. That is, if R1 was 100K, then R2 would be 68K. This provides the
reference voltage. The idea is to have the output go above and below the
reference voltage by about the same amount in order to give you 50% duty
cycle. R3 should be enough to reduce the output voltage by enough to
insure oscillation (but not too much), and will effect the rate. The
.1uf and the 1M form the RC that really determines the rate. I almost
always use a 1M for this because it means a smaller cap. I like using
ultra-bright LED's to keep the current down. Mouser part# 351-3232 gives
a nice glow with good viewing angle and low current.