dale@lamont.UUCP (dale chayes) (10/18/87)
I am (reluctantly) doing an interface between a PBX (probably a Mitel SX-20) and a Magnavox MX-211 INMARSAT (ship earth station) and am in need of a (the) reference that defines (electrikly) a Subscriber Line (SLIC?.) The MX-211 uses a '4 wire' phone line. I already have a '4-wire to 2-wire' conversion that works, and the interface to get the MX-211 to establish a connection through a satellite. What I have yet to resolve is the 'off hook' detector. The interface was built for a Hayes 1200 baud modem and the 'off hook' is done with the other set of relay contacts that only appear to exist in the Hayes 1200s. It seems to me that the 'thing to do' is to supply a current source (as if there was a 'local office' in my 4 to 2 conversion box, and detect 'off hook' by from the current flow. Comments, reccomendations, and a reference are welcome. Dale Chayes snail: Lamont-Doherty Geological Observatory, Palisades, N.Y. 10964 phone: (914) 359-2900 ext 434 net: ...!philabs!lamont!dale fax: (914) 359-6817 -- are we having fun yet?....
brian@casemo.UUCP (Brian Cuthie) (10/27/87)
In article <159@vema.lamont.LDGO.Columbia.edu>, dale@lamont.UUCP (dale chayes) writes: > > I am (reluctantly) doing an interface between a PBX (probably a Mitel SX-20) > and a Magnavox MX-211 INMARSAT (ship earth station) and am in need of a (the) > reference that defines (electrikly) a Subscriber Line (SLIC?.) > > It seems to me that the 'thing to do' is to supply a current source (as if > there was a 'local office' in my 4 to 2 conversion box, and detect 'off hook' > by from the current flow. > > Comments, reccomendations, and a reference are welcome. Dale, you forgot to mention which side of the PBX you would like to interface to. If you want to interface on the instrument side (ie. where a phone would normally go) then you must make something that looks like a phone to the PBX. This really isn't too hard. You just need to have a two wire interface that has an impedance of about 600 ohms and a DC resistance of about 200 ohms or less. This is usually done best through a transformer. To my knowledge, Mitel uses their MH88500 SLIC as the interface on that end. (You can get the specs on that part from Mitel. They sell it in the open market and it's in their data book. I've used them in my own PBX and they're quite nice.) If, rather, you would like to connect to the trunk end of the PBX (the interface that usually connects to the phone company), then you need to build something that looks like a phone line. It should be a 2 or 4 wire interface (depending on the Mitel trunk interface) and it should be capable of supplying about 24 volts and 30 ma into a 200 ohm DC load. It should also have an impedance of 600 ohms. Depending on the requirements of the Mitel PBX you could actually use their MH88500 SLIC. Really, it would be best to get the Mitel data book and look at their SLIC. It will provide some useful information regardless of which interface you actually have to build. Hope this helps... Cheers, Brian ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Brian Cuthie CASE Communications Columbia, Md 21046 (301) 290 - 7443