OK.  I checked the chips at Mitel site.  The MH8612B seems like a reasonable
choice for my project.  As well, a couple of MT8809 crosspoint switch matrix
chips should do the trick.  I have already order a few TelTone call progress
tone generators.

Questions:

- If you have used these, can I assume that the VR and VX are the pair that
(via the matrix) actually connect to the telephone sets??

- Also, would you share how you generate your 90volt ring signal??

John Mullan


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Keelan Lightfoot
Sent: Friday, November 19, 1999 2:15 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Help: Connecting Phones


Over the past week, I have been designing my own PBX, with capability for 16
lines and 4 trunks. I looked at all design options I had available to me for
switching, voice transmission, etc., and the best I have found so far is a
line of ICs by Mitel -- Their SLICs, COICs and analog switch matrix devices.
With very few additional components, you could easily build a PBX.

Have a look at http://www.mitelsemi.com

Also, Teltone's (http://www.teltone.com) dial pulse counter ICs and progress
tone generator ICs are helpful.

Using the Mitel 'system', you can construct a PBX with no transformers or
capacitors in the audio path -- Just connect the junctor on the SLIC to the
analog switching matrix. Connect the right matrix points together and you
have a connected call.

- Keelan Lightfoot