Re: DIY doorphone?

["PatrickLidstone" <patrickl@xxxxxxx>]

--- In ukha_d@y..., "Lee" <lee@v...> wrote:
> Flush with the successfull installation of my BT 2+8 PABX box,
thoughts
> have now turned to the idea of using one of the eight internal
lines as a
> doorphone.
>

Many PBX's have an explicit input for "doorphone ringing" -
shorting
the input typically causes all phones to ring. Any extension can then
answer the door by phoning the extension which has the doorphone
attached. If the PBX supports this function, the extension can be
programmed so that the fact that it is always off-hook doesn't pose a
problem.

If you go the butcher-a-phone route, and your switch supports
grouping of extensions, I suggest using a phone with a progammable
memory. Pressing the memory button then dials the extension group
causing all phones in the group to ring. You also need to find a way
to take the phone off hook/hang up automatically - possible using a
timer circuit of some description?

If you have to simulate an exchange line, it all gets a bit hairy -
you need to build (or buy) a ring generator to fool the PBX into
thinking there is an incoming call and then switch it off when the
off-hook condition is detected. Hardly worth it IMO. Or if you just
want the phones to ring, without establishing a speech path, the ring
generator on it's own would be fairly easy to set up.

HTH

Patrick