Re: Circuit/device to make internal phones ring?

["Patrick Lidstone" <patrick@xxxxxxxxxxxx>]

--- In ukha_d@xxxxxxx, LeeUKHA <mailinglists@v...> wrote:
> Last week I missed a delivery (of new toys) by being the shower when
the
> CityLink van called by.
> Annoyingly I thought I heard the door bell, so he didn't just stick
the
> card in and run...
>
> Anyhow, it struck me that now I have a shiny new VIOM, I could hook it
> up to the doorbell and then get the HA server to ring the internal
> phones just once, rather like the Comfort system...
>
> Despite a good deal of Googling, all I can find are circuit designs to
> make a phone ring, as long as it's NOT actually plugged into a phone
> line. Fair enough as who knows what may happen at the BT exchange by
> putting ringing into the external phone line, but as I've got a PBX
> installed, is that actually a problem? The only problem then is how to
> attach the circuit?
>
> Anyone?

Many PBXs have a special doorphone input for exactly this purpose -
perhaps yours does?

To generate ringing on an existing extension, you need to put a
changeover relay between the extension and pbx, and then feed 40VAC or
so across tip and ring on the extension when the relay is in the
"ring" position. Of course, if the relay is activated whilst a
call is
in progress the call will be interrupted by silence.

Plan B would be along similar lines, but to put the changeover relay
in front of the PBX, allowing all extensions to be triggered from a
single relay. This would bring you closer than you "should be" to
the
BT circuit.

Plan C would be to generate a ringing voltage on an unused trunk
circuit of the PBX. This will ring all the phones that are not
currently on a call, and won't interrupt any ongoing call (you may
even be able to configure a call-waiting style beep).

Patrick