switching the bell wire...

["Paul Gordon" <paul_gordon@xxxxxxx>]

Following the earlier threads about turning off the bell wire, I've spent
the morning grubbing around in the cellar tidying up the phone wiring, and
bringing it all onto a phone patch panel ready for setting it up how I 
want..

I've got a latching relay from Maplins (part NG65V) which I plan to use for
the switching. - Note that there are two reasons why I got a latching one;
firstly, they didn't have any stock available of the first 3 that I chose
(shock horror!), and secondly, although I realise it will require two
output 
ports on my controller, I thought there might actually be some advantage to
a latching relay, namely, power-saving (not necessary to keep the coil 
energised to keep the relay in position), and conservation of state across
power failures. (the relay won't switch under any circumstance *other* than
a signal from the HA controller)

However, there is one disadvantage, which is that because I won't be
keeping 
the relay energised to maintain its state, I won't be able to use the coil
power supply to run an indicator. (I wanted to have an LED to show at a
glance whether the bell wire was on or off...)

Is there any way of using the phone wiring itself to power an LED to show
when the bell wire is connected?. I checked with a meter, and I see the
following:

38VDC across LINE A  and LINE B
36VDC across BELL    and LINE B

Could I therefore put an LED across LINE B and BELL, *after* the relay? -
with the relay closed (BELL connected) I have 36VDC, and with the relay
open 
(BELL disconnected) I would obviously have 0V....  Would this cause
any 
problems? if it's feasible, can anyone suggest a suitable indicator?(I 
presume I'll need to get that down to about 5VDC to be useful?)

Or am I talking total twaddle?

TIA

Paul G.







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