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From: Fred Bloggs
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Subject: Re: How to get CMOS counter to drive a relay?
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Date: Fri, 18 Oct 2002 11:54:33 GMT
NNTP-Posting-Date: Fri, 18 Oct 2002 04:54:33 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
John Fields wrote:
> On Thu, 17 Oct 2002 14:12:43 GMT, Fred Bloggs
>>You're right, the simplest way may be to use parallel spare CMOS buffers.
> The _simplest_ way would be to drive the relay directly from the
> counter's outputs.
> Outrageous? _You_ may think so, but then you've always had problems
> with relays, no?
> Consider this:
> Use a reed switch and wind the coil so the switch's ampere-turns
> requirements are met with the output current available from the
> counter's outputs.
> Wanna try to figure it out, just for fun? You'll get to use all of
> your in-depth knowledge about relay coil aging (???) copper wire
> tempco and manufacturing tolerances. Let's take a nicely sensitive
> reed switch with a worst case 7.5AT sensitivity from -55°C to 125°C
> and see how it goes, OK?
Nope- I would not consider using an ultrasensitive reed in an
environment with large magnetic field strengths.
Why don't you consider this. Use a decoder to select the counter output
used to activate the relay. The decoder output connects to the counter
output through a suitable current limiting resistor and a PNP BE is
connected across a resistor in series with the counter Vdd line. The
single PNP then drives the relay.
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