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'Help: Connecting Phones'
1999\11\18@221008 by John Mullan

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In my endeavours to utilize 16F84 and 12C508 for my own brand of PBX, I am
finding that almost all similar projects by others use transformers to
couple the audio to the voice paths.

I have tried using capacitors to do this but get lousy audio.  (.1uf or 1uf)

Is there a good "transformerless" method??

Am I using improper value caps ( I was going to try 10uf non-polarized
elec.)

This seems to be the last bit of info I need to get to work on this.  I was
hoping to only use transformers (if necessary) on the CO side of the switch
matrix.

Thank you in advance.

John Mullan
spam_OUTjmullanTakeThisOuTspamcgocable.net

1999\11\19@021331 by Keelan Lightfoot

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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

1999\11\19@022136 by Dave VanHorn

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> 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.

Good foundation. Their older analog PBXs are excellent. I still prefer them
to the new digital equipment, especially if there's modems involved.

1999\11\19@084109 by Max Toole

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In a message dated 11/18/99 10:18:26 PM Eastern Standard Time,
.....jmullanKILLspamspam@spam@CGOCABLE.NET writes:

> In my endeavours to utilize 16F84 and 12C508 for my own brand of PBX, I am
>  finding that almost all similar projects by others use transformers to
>  couple the audio to the voice paths.
>
>  I have tried using capacitors to do this but get lousy audio.  (.1uf or
1uf)
{Quote hidden}

I use the Motorola MC34014P Speech circuit.  It works great.

Max

1999\11\19@114433 by V sml

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Keelan,

May I know how much does it cost you and how is it working now?  How
much can you do to the software?

Thanks.

Ling SM

>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.

1999\11\19@183139 by John Mullan

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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 removed}

1999\11\19@183409 by John Mullan

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Finding an older analog PBX board(s) would be too easy.  I'm just trying to
fill my hobby time with some learning and maybe get a practical device out
of it at the same time :)

John Mullan


{Original Message removed}

1999\11\19@201458 by John Mullan

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So now I have what I need as far as parts and sourcing.

I think I'll settle on the MH88612 from Mitel as the SLIC.

I'm also going to get a couple of MT8808 8x8 crosspoint switches.

Both of these are available from Electrosonic here in Ontario.

MH88612  $16.87CDN
MT8808   $10.73CDN

Now, as I understand it, I would use the SLIC chips at the CO side of
things.  Would this be correct??  Or is there another interface chip that I
may need??

John Mullan

-------------------------------------
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

<snip>

Have a look at http://www.mitelsemi.com
Also, Teltone's (http://www.teltone.com) dial pulse counter ICs and progress

<snip>

- Keelan Lightfoot

1999\11\19@222303 by Keelan Lightfoot

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>So now I have what I need as far as parts and sourcing.
>
>I think I'll settle on the MH88612 from Mitel as the SLIC.
>
>I'm also going to get a couple of MT8808 8x8 crosspoint switches.

Wait!! I would use a SLIC with a single wire matrix switch interface (88500,
88510/11) You will only have to buy half as many matrix switches if you do
it that way.

>Now, as I understand it, I would use the SLIC chips at the CO side of
>things.  Would this be correct??  Or is there another interface chip that I
>may need??

You would use the SLIC on the station line side of your PBX, and a COIC
(Central Office Interface Circuit) for the CO side of your PBX.

Have a look at:
www.bzzzzzz.com/beehive/keelanl/PBXdiag.gif
for a block diagram of a simple PBX using Mitel's devices. All that is shown
in that diagram are the voice connections, you'll have to figure out control
logic on your own :)

And, no, I have no financial interest in Mitel :) They just make good
products that work really well together :)

- Keelan Lightfoot

1999\11\19@223323 by Keelan Lightfoot

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>Keelan,
>
>May I know how much does it cost you and how is it working now?  How
>much can you do to the software?

Like I said, I'm still in the design stage of things. I still haven't yet
decided on what CPU I am using -- I need a lot of I/O because of the strange
architecture I am designing this PBX with. I'm thinking either a Zilog Z80
or a PIC17C44.

I have calculated that building a 16/4 system would cost a lot of money
(~$500 Canadian), that is why I am going with a modular design (a card for
each line), so that I may build a small PBX and upgrade it as I can afford
it. A 2 line, 1 trunk system would probably cost ~$100 Canadian to build,
not including time :)

I haven't settled on a 'mental image' of the software yet, as the hardware
surrounding the CPU is very modular -- there will be 24 slots in the system,
into which any type of card can be plugged - DTMF receiver, tone
transmitter, line card, trunk card etc. -- most PBXs have a slot that only
works with the card designed for that slot (DTMF receiver goes in the DTMF
receiver slot)

- Keelan Lightfoot

1999\11\20@063810 by Picsend

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Hi John,

May I suggest an idea, separate in two parts, peripherals and heart:
- lines interfaces (internal or external, it's near the same).
- control with 2 pics using a one multiport memory like PLX.

When a ring or hang-up occurs, line interface send wait message for external
call or a waiting for dial ring for internal. The two Pics try each line :
one stop when it get an interruption and the connecting work. With dual port
ram, one Pic can lock line and the other Pic see when it is busy.

You can handle 4x8 lines without problems.

Hope it help.
SP

1999\11\20@202013 by John Mullan

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Keelan,

Sounds like maybe you live in Canada.  If so, me too.

Where do you purchase your Mitel Chips??

John Mullan


{Original Message removed}

1999\11\21@001517 by Keelan Lightfoot

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>Keelan,
>
>Sounds like maybe you live in Canada.  If so, me too.
>
>Where do you purchase your Mitel Chips??

I live on the BC side of the BC-Alberta border, in the south of BC.

I haven't purchased any chips yet, (I'm poor (:), and have only been
throwing this idea around for a week or so), but I was going to buy them at
Insight Electronics (http://www.insight-electronics.com) (they were the only
people I could find that sells them), but it looks like I might be better
off with Electrosonic, so I will probably be ordering them from them. Hmm..
I'm looking at Electrosonic's results, and it looks like a minimum purchase
of 100 per device. Okay, back to Insight :)

- Keelan Lightfoot

1999\11\21@105733 by John Mullan

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Interesting.  My sister is going to work the ski season near Banff.  She's a
chef.

Well, I suppose Insight sounds a bit better.......

I was hoping to get off a little cheaper in starting this project.  I have
all the micros I'll ever need for this.  From your knowledge, is the MH88500
a better choice than the MH88612??  Is this because the MH88500 is "single
wire"??

I suppose it might be a little cheaper to use the CO interface chips as
opposed to discrete interface.

John Mullan


{Original Message removed}

1999\11\21@114552 by John Mullan

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I'm thinking that, with exchange and stuff, Electrosonic would be better for
most of the devices.  Can't help but wonder about the MH88500 being a 100
minimum!!!  That is probably because they have none in stock.

But the MT8808AE and MH88634B are good bets.  If the MH88612 is usable in
the design, then Electrosonic can be used as well.

Teltone in Ottawa will sell 10 of the M991 (I think that is correct) for
$6US.  These are the Call Progress Tone Generators.  That's cheap and they
send a free sample (I've yet to receive mine :)

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

John Mullan


-----Original Message-----
From: pic microcontroller discussion list
[.....PICLISTKILLspamspam.....MITVMA.MIT.EDU]On Behalf Of Keelan Lightfoot
Sent: Sunday, November 21, 1999 12:18 AM
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
Subject: Re: Help: Connecting Phones

I'm looking at Electrosonic's results, and it looks like a minimum purchase
of 100 per device. Okay, back to Insight :)

- Keelan Lightfoot

1999\11\21@155916 by Keelan Lightfoot

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>Interesting.  My sister is going to work the ski season near Banff.  She's a
>chef.
>
>Well, I suppose Insight sounds a bit better.......
>
>I was hoping to get off a little cheaper in starting this project.  I have
>all the micros I'll ever need for this.  From your knowledge, is the MH88500
>a better choice than the MH88612??  Is this because the MH88500 is "single
>wire"??
>
>I suppose it might be a little cheaper to use the CO interface chips as
>opposed to discrete interface.

Yes, the 88612 has separate voice transmit and voice receive wires, meaning
that 2 matrix switches are needed (1 for Voice TX, another for Voice RX),
and keeping track of the switching matrix would be a bit more complex
because you would have to connect the VX pin of one SLIC to the RX of
another, and vice versa. With the single junctor wire interface, you connect
the junctor pin of one SLIC to the junctor pin of another. Mitel doesn't
make any COICs with a juctor pin, so you have to use their '4' wire to '2'
wire converter (actually 2 wire to 1) to connect the COIC to your system
(MH88524).

I'm in Fernie, another ski town :)

- Keelan Lightfoot

1999\11\21@160324 by Keelan Lightfoot

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>I'm thinking that, with exchange and stuff, Electrosonic would be better for
>most of the devices.  Can't help but wonder about the MH88500 being a 100
>minimum!!!  That is probably because they have none in stock.

I agree with you there, but maybe Insight's Calgary distributor can sell us
the components we need, avoiding exchange.

>But the MT8808AE and MH88634B are good bets.  If the MH88612 is usable in
>the design, then Electrosonic can be used as well.

Thanks, I'll get mine from there :)

The MH88612 can be used, but it will make hardware and software a little
more complex. Also, I don't know how a 3 way call could be created with the
MH88612:

2 way call:
L1   L2
Vx---Vr
Vr---Vx

3 way call:
L1   L2   L3
Vx---Vr---??
Vr---Vx---??

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.

>Teltone in Ottawa will sell 10 of the M991 (I think that is correct) for
>$6US.  These are the Call Progress Tone Generators.  That's cheap and they
>send a free sample (I've yet to receive mine :)

When I ordered a sample from Teltone, it took about 4 months to arrive :(

>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

1999\11\21@171032 by D. F. Welch

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A quick question, do any of these chips provide a ring signal function?

Thanks for your help.

-Dan

At 01:12 PM 11/21/99 -0700, you wrote:
{Quote hidden}

-Dan
amerscispamspam_OUTflash.net

1999\11\21@175733 by Keelan Lightfoot

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>A quick question, do any of these chips provide a ring signal function?

They need an externally generated ring signal. I am currently working on a
ringing signal generator. I'll post my schematic to my web-page when I get
it finished.

- Keelan Lightfoot

1999\11\22@074043 by paulb

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Keelan Lightfoot wrote:

> Also, I don't know how a 3 way call could be created with the MH88612:
> With the MH88500, just tie the junctors together.

 Is that actually documented so?  I can't see how they do it.  In fact,
I still haven't figured (without recourse to the documentation which I
trust *is* readily available on the site) whether this system is analog
or digital.

 If analog, then duplexing must be on the basis of a characteristic
impedance and grounding would be *critical* to the system.  Tying three
lines together would create an impedance mismatch which would increase
side-tone to each station as it speaks.

 If digital, then it uses either time-division multiplexing (CSMA/CD)
which would be adaptable to multiple stations, or ternary multiplexing
which would have exactly the same problem tying multiple lines as an
analog system, but would be far more noise-tolerant.

 If you know the answers to the above, *then* you might be in a
position to figure the two-wire version relatively easily.
--
 Cheers,
       Paul B.

1999\11\22@163536 by Keelan Lightfoot

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Paul B. Wrote:

>  Is that actually documented so?  I can't see how they do it.  In fact,
>I still haven't figured (without recourse to the documentation which I
>trust *is* readily available on the site) whether this system is analog
>or digital.
>
>  If analog, then duplexing must be on the basis of a characteristic
>impedance and grounding would be *critical* to the system.  Tying three
>lines together would create an impedance mismatch which would increase
>side-tone to each station as it speaks.
>
>  If digital, then it uses either time-division multiplexing (CSMA/CD)
>which would be adaptable to multiple stations, or ternary multiplexing
>which would have exactly the same problem tying multiple lines as an
>analog system, but would be far more noise-tolerant.
>
>  If you know the answers to the above, *then* you might be in a
>position to figure the two-wire version relatively easily.

I could duct-tape 48 SLICs together, wrap them in aluminium wire, dip them
into a solder bath for 4 hours, pull them out, douse them in vanilla
pudding, parade them down an obscure avenue in Chicago, paint them with
stars and stripes, nominate them for president, back them out in a shroud of
controversy, put them on my head, spin around 39 times, connect them to a
450 VAC, 46.9 Hz, 900 KA power supply then smuggle them into Manitoba and
buy a bottle of water for them, followed by spitting on them and gluing
them, with sheep mucus, to the front right fender of a '58 ford Fairlane. I
could then use an oxygen lance and cut the front half of the Fairlane off
and sell it to a podiatrist, but not before peeling of the 48 SLICs and,
using woodworkers glue, 3 cans of baked beans, a bottle of MSG and a steam
roller, affix them to a PCB made out of wax, nail filings and kitty litter.

Am I in a position to do that?

- Keelan Lightfoot

1999\11\22@214649 by John Mullan

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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...

@spam@jmullanKILLspamspamcgocable.net

John Mullan


{Original Message removed}

1999\11\22@214703 by John Mullan

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OK. I forget!  What is your web page????


-----Original Message-----
From: pic microcontroller discussion list
[KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU]On Behalf Of Keelan Lightfoot
Sent: Sunday, November 21, 1999 6:01 PM
To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU
Subject: Re: Help: Connecting Phones


>A quick question, do any of these chips provide a ring signal function?

They need an externally generated ring signal. I am currently working on a
ringing signal generator. I'll post my schematic to my web-page when I get
it finished.

- Keelan Lightfoot

1999\11\22@220528 by Wagner Lipnharski

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> >A quick question, do any of these chips provide a ring signal function?

Using a small power transformer, lets say 110Vac x 30Vac (center tap) x
300mA, two TIP30 transistors (or IRF530 FET) and 12Vdc power supply are
enough to generate around 60Vac under 20Hz, driven by a
microcontroller.   The ring generation is not a problem at all.  The
problem is to recognize the ringing phone just answered the call and the
ringing generation should stop.  One of the possibilities is measuring
the voltage over the phone line *when it is not ringing*, if it is lower
than 16Vdc then the calling phone is off hook, if it is above 16Vdc then
keep ringing.  Some extra current measurement could be done even when
ringing...

Wagner

1999\11\22@223047 by Wagner Lipnharski

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... I forgot to say, I may have few hundreds transformers 115/230 |
20/40 Vac, 300/150mA, pulled from brand new phone line simulators.  If
someone is interested, take a look at:
http://www.ustr.net/parts/trafo.shtml

Wagner.

1999\11\23@173834 by John Mullan

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The SLIC chips from Mitel provide a loop current detect and can be made to
disconnect the relay to stop ringing.

John Mullan


{Original Message removed}

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