Re: Doorbel via telephone

Ross Herbert wrote:
On Mon, 04 Feb 2008 16:39:54 +0100, VMI <VMI@xxxxxxxxxxx> wrote:

:Hi,
:As I've been asked (family) to construct a doorbel - PABX interface I :have to resort to the ingenuity of fellow readers.
:What is the aim?
:When the doorbel is pushed, all telephones connected to the in-house :pabx (1 external line, 6 internal lines, 2 wire) have to ring.
:Any of them can accept the call and talk to the kind of "parlefoon" on :the door.
:This "parlefoon" is connected as telephone nr6 of th PABX.
:A two way communication is then setup.
:There is a method to let all connected telephones to ring when a :particular sequence of digits is sent to the PABX.
:1. How to generate this sequence of tones.
:2. How to establish a conversation.
:
:Thanks
:Zilog


I believe you are wasting your time if you try to do this. For a start nobody
can advise you unless they intimately know the existing PBX system currently
installed in your premises. Even then, it is highly unlikely they would know all
the intricacies of that particular PBX, facilities, programming modes,
circuitry, hardware add-ons etc, etc. And they would be even less likely to know
how to advise you to hack into the system to incorporate your add-on circuitry.

You would be far better off, and it would be cheaper in the long run, to buy an
off-the-shelf system such as the Panasonic KX-TA824
http://www.panasonic.com/consumer_electronics/communication_systems/pdf/KX-TA824_BusSpec***.pdf
or even the older obsolete KX-TA308 which may be available 2nd hand or on Ebay,
which provide most if not all of your requirements. These systems have a door
telephone and call forwarding. If the door phone is activated it will ring a
selected phone but if this isn't answered in a preset number of rings, it
forwards the call to another phone, and so on. While these systems also include
all-phones paging with call pick-up, this function is not activated from the
door phone. If it were possible then your problem would be solved. It may be
possible to build an add-on circuit for these systems to intercept the door
phone call and then activate the paging/call pickup function, which would be far
simpler than what you propose.
Thanks for the reply.
But I have to ask you to read all the postings before answering.
As you could have seen all that's needed is an interface between the doorbel (eg parts of an old telephone?) and the pabx.
One internal line is used for this doorbel (telephone).
After pushing the doorbel (= same as taking the phone Off-Hook) the interface must generate a sequence of known numbers (eg 6 0 0 - six zero zero) and when this sequence of numbers is send to the pabx ALL telephones ring one after the other. A feature excisting in the pabx!
If any of them will answer a conncetion is created.
AFter the answering phone is placed On-Hook, the connection is interupted.
Only other problem remains,; if after a fixed number of rings (eg 10) the ringing will stop.

So there are two main items:
1. Generate a known sequence of numbers (DTMF code)
2. A Ringing counter that resets the doorbel interface.

Voila.
This must clarify the problem a b it more.
There is no option of buying another pabx. I'm looking for an interface to be build.
Tips and links to schematics are very usefull.
No new PABX.

Thanks,
Zilog
.

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