A related non obvious thing that happened to me the other day: a relay driv= ing circuit that worked fine the first time round stopped working when I bu= ilt a second. The relay was a standard 5v non latching miniature type bough= t from maplin as " BT type 47 relay". Eventually I noticed that the second relay I bought was a different part ( = even though sold as the same maplin part number ) and this one had a coil t= hat only operated in one polarity! I guess there is a permanent magnet I'm = there to reduce the operating current or something. I was completely surpri= sed by this having spent far too long probing around convinced that the sec= ond copy of the driving circuit must be at fault. Maybe one day this tale w= ill save one of you the same head scratching :)=20 Cheers,=20 Robin. On 25 Oct 2011, at 21:01, "Bob Blick" wrote: > On Tuesday, October 25, 2011 11:54 AM, "alan smith" wrote: >> http://www.aislu.com/documents/HG30T_EN_S101027V1.pdf >>=20 >> If you look at the drive principle, its saying a position DC to latch, >> and a negative DC to unlatch? Is this the same thing as just reversing >> the DC voltage on the coil? Ive not used latching relays before.... >=20 > Yes. >=20 > Relays in home thermostats use latching relays with that method of > operation, also they can have a center-tapped coil so you drive one side > or the other, same idea of reversing magnetic field. A permanent magnet > inside the relay keeps the relay latched. >=20 > Cheers, >=20 > Bob >=20 > --=20 > http://www.fastmail.fm - Same, same, but different... >=20 >=20 > --=20 > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .