From: Richard Lamb
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Subject: Re: How to get CMOS counter to drive a relay?
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NNTP-Posting-Date: Sun, 20 Oct 2002 01:42:24 EDT
Organization: Prodigy Internet http://www.prodigy.com
Date: Sun, 20 Oct 2002 05:42:24 GMT
Dave VanHorn wrote:
> > I simply rembered a guy, 25 years ago, who had wired some
> > 7-segment led displays to a clock chip, not using any
> > transistors at all. The chip ran pretty hot, but it
> > worked okay. I wondered what would happen - call it an
> > experiment - if you tried hooking up that 20mA relay
> > without a buffer.
> If you added a protection diode across the relay coil, it might work.
> It wouldn't be a good idea though, unless the chip is rated to sink or
> source that much current, and it's internal voltage drop at that current is
> low enough that the relay will always pull in.
> It's the sort of thing that you see in hobby designs, where it might work
> for me, with my chips and my relay, but not for you with similar chips and
after "hand selecting" the relay?
> If you stay within the specs, then it's guaranteed to work. If you violate
> the specs, then it still may work, but the next one may not. I've seen
> PhD engineers make that mistake. (and had to clean up the mess too)
I worked for a while as a preipehral design engineer at a large
I had two phd electronics types replace a circuitboard - without the
And another try to direct inject video into his TV set.
The little green radio shack jumper he used to "ground" his computer
to the TV chassis - flashed - once.
The are rare, but so entertaining!