On Tue, 02 Feb 2010 14:54:02 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Geo wrote:
Sounds a bit like my Danfoss TP75. It uses an Omron latching relay type
G6CK-2117P which works off a 20mS 3V pulse:-
http://www.omron.com/ecb/products/pry/121/g6c_2.html

Interesting - but nothing like those on my board. I no longer have it so
can't take pics. The description isn't that clear - does it take (near)
zero current when made or just a reduced amount? For long battery life it
would need to be zero. Nor did the noise it made when the 'switch'
operated sound anything like a relay.

No current at all. Imagine a balanced metal arm pivoted in centre and a coil at
each end with some remanent magnetism. A current pulse through either coil is
sufficient to overcome the small static magnetic pull and trip the bistable to
the other condition. The Danfoss WP75H uses a much larger Gruner 703H to switch
up to 25A for an immersion heater.

This article has a short explanation and some driving circuits:-
http://www.electronicsweekly.com/Articles/2008/11/21/44977/circuits-drive-single-coil-latching-relays.htm

--
Geo