PBX design help.how to start???

[eng_ahmed22]

hi every body.

i want to build a PBX, with only internal telephon lines (no CO interface at the begining) let us say 4 internal lines,
can any body suggest schamatic or block diagram or anything to start???
i have some experience (2 years) in installing SIEMENS PABX (up to 500 line) now i hope to start to build my private PBX.
thanks alot for ur time
have a nice day

AHMED

 

[IanP]

Maybe this project will be of any help to you:

Home made PBX

Specifications:

-Eight telephone extensions with roughly telco spec voltages and currents (48V onhook, 90VRMS 20Hz sinusoidal ringing, about 25mA loop current offhook.) Ring trip is sub-spec but can handle at least 3 "500" type rotary dial telephone sets in parallel without false tripping. Lines are not balanced, nor is one side ground.

-One central office line capable of inbound calls (ring detector) and outbound calls with DTMF and pulse dialing (selectable, independent of the type of extension phones. That is, the PBX can convert tone-pulse and pulse-tone.)

-Three internal voice buses, meaning up to three calls in progress simultaneously.

-Telco standard call progress tones (dial, busy, fast busy, audible ringing.)

http://wandel.ca/homepage/pbx.html

Regards,
Ianp