Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: Larry Lippman Newsgroups: comp.dcom.telecom Subject: Building a 1A2 Key Service Unit Message-ID: <11249@accuvax.nwu.edu> Date: 23 Aug 90 17:00:57 GMT Sender: news@accuvax.nwu.edu Organization: TELECOM Digest Lines: 56 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 589, Message 2 of 8 In article <11088@accuvax.nwu.edu> atn@cory.berkeley.edu (Alan Nishioka) writes: > I am trying to build a box for my five line key system phone. I want > it to flash the lights and do automatic hold. > The system I was going to time has been dismantled and replaced with > Panasonic phones with LEDs so you can't tell which line is ringing... I would suggest that you look around for a used key service unit (KSU) with 400-type line cards, which will perform all of the functions you desire. With the extensive proliferation of electronic key telephone systems and "mini" PABX's, such used KSU's often sell for very little money - especially at say, an amateur radio flea market. Design of a 1A2 key system to work with your telephones is not a trivial effort. It's not that difficult, either, but you will spend some time doing it. If you are determined to build it from scratch, I would suggest a "non-traditional" approach. Use a microprocessor with I/O expander for all logic and timing functions. Detect ringing and loop current using optoisolators. Drive the lamps with ten volts DC switched by suitable current drivers. Sense the A-lead ground closures preferably with optoisolators. Use a reed relay to place a 300 ohm hold resistor across the telephone line. In summary, your microprocessor would have five ringing detector inputs, five loop current detector inputs, five A-lead inputs, five lamp outputs, five hold relay outputs, and one common audible relay signal output. Everything else is software. :-) The lamp signals and interrupted common audible signal sequence would be generated under software control. Yet another alternative would be to obtain just the 400-type line cards, make your own card cage, and build a power supply and interrupter circuit yourself. All you need is -24 volts DC for the 400-type line card control power and ten volts AC for lamps (do not substitute DC for AC on the ten volt lamp circuit with newer 400-type line cards since they use triacs or SCR's for lamp control instead of relay contacts). The standard KSU interrupter operates from the ten volt AC supply. You will also need 18 volts AC or 20/30 Hz ringing for common audible signals, depending upon whether you use buzzers or ringers. > Does anyone have the light flashing cadences? (frequency and duty > cycle). Lamp flash for incoming calls is interrupted at 60 IPM with a 50% on-duty cycle (i.e., 500 ms on, 500 ms off). Lamp wink for hold is 120 IPM with an 80% on-duty cycle (i.e., 400 ms on, 100 ms off). Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry