Ok.  So now I have to add yet another chip (MH88524).  When I started this
idea I figured it would be a little easier.  But that's the fun of it I
guess.

My PBX is going to be designed for typical residential use.  2 CO and 8
extensions.  I'll allow for two intercom paths, external audio path and
maybe a paging path.

I originally though that I could use some pics for much of the "subsystem"
stuff.  Like one per extension and one per CO and 8051 (actually AT89C52) as
the brains with configuration possible via RS232.  I have about 30 PIC16C84
chips that probably won't get used much here!!!

Now I'm going to start getting the Mitel chips (a little at a time,
Christmas budget you know) and then start planning out my circuit.  I figure
I'll get a couple of the SLIC chips and the crosspoint switch first.  I can
quickly get a PIC to switch the matrix and connect/disconnect two phones.
After practicing that, I'll build up from there.  Probably do an
"auto-seize" and make sure I can make a call.  From this point on I'll move
on to the AT89C52 and put some real functionality into it.

Now that that is all said, refering to an early message of yours, I think
that the end product will cost something more than $200 CDN.  The price of
the chips and tax passes that (even considering the ones I have around ie;
uController).  Then there are the relays, powersupply etc.

But it will make for quite a project that I expect will keep me busy towards
late spring or summer.

If you would like to collaborate from time to time, you can email me
direct...

mailto:jmullan@cgocable.net

John Mullan


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Keelan Lightfoot
Sent: Sunday, November 21, 1999 4:06 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Help: Connecting Phones


With the MH88500, just tie the junctors together. If you connect too many,
the audio would sound quiet, so in my system, i'm going to limit the number
of stations on one line to 3.

>If the MH88634 is necessary (as per my previous email) then I guess Insight
>(out of Alberta) would be the place for those!

I would recommend it for your CO lines, because it is compatible with the
Mitel 'system'. Also, the chances of Mitel's COIC causing problems with your
telco's phone line is minimal. Keep in mind that for every 2 MH88634s you
will need 1 MH88524, to convert them to a single wire interface.

What size PBX are you planning on building?

- Keelan Lightfoot