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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: 68HC11 and relays
Organization: The Armory
Date: Wed, 14 Sep 1994 09:53:28 GMT
Message-ID: <Cw465A.6Ly@armory.com>
References: <000C3FB8.fc@bcsmac.org> <352afu$9du@handler.eng.sun.com>
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In article <352afu$9du@handler.eng.sun.com>,
Chuck McManis <cmcmanis@Sun.COM> wrote:
>Jake V. Bouvrie (Jake_V._Bouvrie@bcsmac.org) wrote:
>: does anyone know how i could trigger a relay to drive a motor, or to 
>: just drive the motor, using the regular....say PORTC pins....theres 
>: not enough current to flip then and i was wondering how to get a 
>: switch like action...a NPN transistor?
>
>The simplest way is to use a Peripheral Driver chip like the DS3632N
>(available from DigiKey 1-800-DIGI-KEY, for $3.68). The cheapest way
>is a 2n2222A transistor. Use this circuit:
>			Relay Voltage
>                              |
>			      +----o
>			      +----o To relay
>			      |
>			     /|
>		    1K	   |/ -
>	PORTC o---\/\/\/---|  ^ 1N4001 Diode
>			   |\ |
>			     v|
>			      |
>			     Ground
>--
>--Chuck McManis	   All opinions in this message/article are
>FirstPerson Inc.          those of the author, who may or may not
>Internet: cmcmanis@firstperson.COM   be who you think it is.
--------------------------------------
That's well and good, Chuck, but why don't you think we shouldn't have the
protective free-wheeling diode across the relay coil taps instead of across
the 2N2222??? I know we might like to keep the downward thrust of the
coil's inductance out of the C-B junction, but the diode the way you have
it wouldn't do it anyway! It's backwards with respect to the coil discharge
potential's direction, and we can't very well turn it around, now can
we??!:)
-Steve Walz   rstevew@armory.com

