Path: utzoo!attcan!uunet!ginosko!gem.mps.ohio-state.edu!uwm.edu!bionet!ames!pacbell!sactoh0!americ!erk From: erk@americ.UUCP (Erick Parsons) Newsgroups: sci.electronics Subject: Re: Latching Relays Message-ID: <2030.AA2030@americ> Date: 21 Sep 89 20:18:27 GMT Followup-To: sci.electronics Distribution: na Lines: 57 Expires: Keywords: From: atn@cory.Berkeley.EDU (Alan Nishioka) Message-ID: <17419@pasteur.Berkeley.EDU> >For a friend's mechanical engineering project I needed a circuit that >latched. I built a circuit using two SPDT relays in which power through >one coil closed a switch which energized the second coil which closed a >switch which energized the first coil, or something like that :-) Kinda >like an RS latch. This worked fine for my application, except there was >a condition where if the wrong switch was closed, the system would >oscillate. A very common latching circuit (for motor control) is to use one relay with two sets of contacts. It is a DPDT relay. ^^^ It requires three wires in the control conduit, two switches: SPST momentary contact, one normally open and one normally closed. 1st set of contacts for control _________ Hot | | ___ | ------o-----------|/|-----------o-------------- . . --o | | | | o-----o-----------| |-----------o-------------- .---. --o | |_________| | | C |-----o------------O------------o-----------------------o I | L Gnd _________ | | o-----------|/|-----------o | | o-----------| |-----------o |_________| 2nd set of contacts for load -----------symbols used------------ |/| normally closed contact of relay | | normally open contact of relay .---. normally closed momentarily opened manually operated switch ___ . . normally open momentarily closed manually operated switch -- ------------------- // ---------------------------------------------------- Erick Parsons // Knowledge is little more than knowing the questions ------------- // erk@americ.UUCP or ..ames!pacbell!sactoh0!americ!erk Sacramento Ca \\ // GEnie: E.PARSONS %-) Hamatuer Radio N6RZB -------------- \X/ --------------------------------------------------------