On Tue, 15 Apr 2008 18:38:04 +0100, Mr Sandman wrote:

Hi all,

its been a while since I played with electronics, so could do with some
advice.

I have 2 magnetic door locks, keypad operated to control access into my
house. I also have a mains power smoke alarm system.

what I want to do is use a relay operated by the smoke alarm when
sounding to turn off the mag locks to allow people to leave with out
having to get their fobs out.


So the maglocks de-energise to release, I assume. That's normally the
case.

system was working fine with one mag lock, but now I have two I have a
problem. the smoke alarm when operating shorts out 2 wires going to the
one maglocks power supply.

So you have separate power supplies for each maglock now?

the electricians has simply connected those
wires to to the same connections in the new power supply. the problem
is now that if someone opens the back door with a fob, the front door
also unlocks! and vice versa.

So both maglocks have now been put on the same power supply, fed from the
alarm panel, or both maglocks are fed from the same alarm panel terminals?

I was thinking about using diodes to try
to get round this problem. I'm not sure if I have explained the set up
very well..so ask away if you have any questions!



To use two maglocks you need two sets of terminals in the alarm panel,
one pair for the front maglock and the other for the back one. They have
to be wired to separate terminals otherwise your system won't work - as
you've found out. If you only have a single set of terminals then you'll
need to look for a new panel or a suitable second-door adaptor (if one is
available for that unit). It's quite possible that the electrician has
connected your panel in the only way possible!

For the smoke alarm you need to add a 2-pole relay, operated by the
signal from the smoke detector. Each pole of the relay is then connected
in series with a maglock. From your description it sounds as if the alarm
has a single volt-free contact, so you need to power the relay from
somewhere - probably at 12 or 24v via a transformer as such contacts are
rarely rated for mains voltage. You would use the normally-closed
contacts on the relays so that they cut off the maglock supplies when the
relay operates.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info http://mixpix.batcave.net
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