Path: utzoo!mnetor!tmsoft!torsqnt!jarvis.csri.toronto.edu!rutgers!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Latching Relay - does such a thing exist
Summary: Relay latching circuits...
Keywords: relay, latching
Message-ID: <3397@kitty.UUCP>
Date: 21 Sep 89 02:15:06 GMT
References: <3558@dgis.daitc.mil>
Organization: Recognition Research Corp., Clarence, NY
Lines: 48

In article <3558@dgis.daitc.mil>, generous@dgis.daitc.mil (Curtis Generous) writes:
> I have an application where I need to activate a SPDT set of contacts
> such that the toggle action does not release after coil voltage is removed.
> And I should then be able to toggle back the contacts with another pulse.
> The best analogy is a SPDT RELAY that latches in the activated position until
> another pulse comes and toggles it again.

	There are several options:

1.	You can get latching relays with various contacts from such vendors
	as Guardian, Magnecraft, Potter & Brumfield, etc.  These relays
	fall in two categories, with one category using a separate operate
	and a separate release coil, and with the other category using
	a single coil with an escapement mechanism such that the contacts 
	change state alternately with every pulse.  These coils are
	available in both AC and DC voltages.  A rotary switch driven
	by a Ledex rotary solenoid is another form of this device.

2.	You can get relays which are magnetically bistable and have an
	operate and a release winding.  The two windings can be connected
	using the contacts such that a single pulse will alternately
	operate and relase the relay.  The vendors in (1) above also much
	such magnetically bistable relays; they are also common in miniature
	sealed can variety as used in military applications.

3.	You can build a relay flip-flop with two DPDT relays and two 
	resistors so that a signal (either ground or battery) will
	alternate the relays, and in effect create the action you desire.
	However, this approach requires that some power be available at
	all time to maintain the state of the relays.

4.	You can build a relay latching circuit using a single relay with
	two normally open contacts (one of which is needed for the load)
	and a single resistor such that alternate momentary application
	of battery and ground will cause the relay to change state.
	However, this approach also requires that some power be available
	at all time to maintain the state of the relay.

5.	You can implement (3) or (4) using a large variety of discrete
	or integrated solid-state circuits.

	If you want the basic mechanical latching relay, chances are that
you can pick one up for a few dollars at a surplus store.

<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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