control a latching relay with one switch?

[foxsam]

I might be missing the point but can't you just use a DPDT momentary switch to reverse polarity to the latching relay? it would only use the battery while you press the switch and since its a DPDT there is no need to flip flop.

[Steerpike]

The latching relays that I happen to have are German-made Haller, with a dual coil - one to latch, the other to unlatch. And two pairs of change-over contacts.

With that type of relay, this circuit will do. You may have to tweak the value of the capacitor, if the relay chatters when holding the pushbutton in. (I took at guess at 470uF, as low as 100uF may work)

NO=normally open, NC= normally closed.
The other pair of contacts can be used on whatever load you like.

[Eva]

If you can find a latching relay with multiple contacts, you can use one of them to remember the state.

[eclectic2k]

Originally posted by bluebeard
I need the previously chosen state to stay the same when the component is returned to power.

though this is all far too late to be of use to the OP, a few comments:
(btw, did you build something to your satisfaction?)

I usually consider it a feature that my amps and such, to default powered off after return to power. I'm paranoid about things not being stable for a while after power failures and such... but that doesn't meet all circumstances or needs I suppose. -- I used some 4000 CMOS logic to integrate a momentary push button and 12v trigger control.

Steerpike seems to have found the simplest solution to this in what looks like the perfect answer if you can get the right relays. (simplest besides a nice latching power switch ;-)

I'm always surprised what can be done with the right basic building blocks, even standard non-latching SPDT relays. this "app note" from DLC parts is nice: http://www.dlcparts.com/images/BoschGuide.pdf

-CK