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'[PIC]: Modulated pulses'
2000\08\18@164715 by igorp

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Hello all:

I would like to get any help how to find a busy signal on telephone line by
a PIC knowing exactly neither the modulation frequency nor the length of
pulses.
Could someone tell me where to look for a theory or some example?

Thanks in advance

Igor

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2000\08\18@215528 by Dan Michaels

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Igor Pokorny wrote:
>Hello all:
>
>I would like to get any help how to find a busy signal on telephone line by
>a PIC knowing exactly neither the modulation frequency nor the length of
>pulses.
>Could someone tell me where to look for a theory or some example?
>


I think most of the following are correct:

US TP SYSTEM
============
D.C. Line Voltage (Talk Battery) - 48v with receiver on-hook, red wire
(ring) negative, 5v for off-hook (with 50-1000 ohm d.c. load on line).

Ring Signal - 20-90 vp-p, at 20-40 hz.

Dialtone - dual 345 and 440 hz sinewaves.

DTMF Tones - 1 high-band plus 1 low-band sinewave at frequencies shown in
DTMF Table, at max transmission level of 0 dBm averaged over 3 sec (approx
24.5v RMS), for minimum of 50 msec duration and 45 msec interdigit time.

Busy Signal - dual 480 and 620 hz sinewaves, 0.5 sec on, 0.5 sec off.

Ringback Signal (simulates phone being rung up) - dual 440 and 480 hz
sinewaves, 2 sec on, 4 sec off.

Receiver Off-Hook Tone (when someone forgets to hang up the phone) - quad
1400, 2060, 2450, and 2600 hz tones, pulsed at a 5 hz rate.

Speech Signals - 200 - 3400 hz, bandlimited.
======================


I also have an appnote that shows a number of these signals on
a scope display:

AN-PTB04 - Telephone System Testing Using the PTB

http://www.sni.net/~oricom/appnotes.htm

best regards,
- Dan Michaels
Oricom Technologies
===================

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2000\08\19@084521 by Bob Ammerman

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All of the below is nominally correct. Unfortunately you will find quite a
bit of variation in the real world, especially on PBX and key systems used
in businesses.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2000\08\20@095037 by igorp

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Thanks guys,

Bob just defined my problem. The task is to recognize a busy signal from any
PBX. It's rather about recognizing a signal with some stable frequency. I
don't believe someone would be able to whistle into a mike a busy signal
accurate enough :-).

Igor Pokorny

> {Original Message removed}

2000\08\20@095905 by Scott Dattalo

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On Sun, 20 Aug 2000, Igor Pokorny wrote:

> Thanks guys,
>
> Bob just defined my problem. The task is to recognize a busy signal from any
> PBX. It's rather about recognizing a signal with some stable frequency. I
> don't believe someone would be able to whistle into a mike a busy signal
> accurate enough :-).

Perhaps, but I know of someone who could whistle DTMF tones accurately enough to
dial phone numbers! That same person has spent several years in jail and is now
not allowed near a computer. Any guesses?

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2000\08\21@140246 by jamesnewton

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I've added Dans info to the existing data at
http://techref.massmind.org/pots
aka
http://techref.massmind.org/techref/default.asp?url=pots

---
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http://techref.massmind.org
All the engineering secrets worth knowing

{Original Message removed}

2000\08\21@142554 by Dan Michaels

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Jim Newton wrote:
>I've added Dans info to the existing data at
>http://techref.massmind.org/pots
>aka
>http://techref.massmind.org/techref/default.asp?url=pots
>

I found that info a couple of years ago scattered between half
a dozen articles in various magazines, and don't know of any
definitive source, and never had an opportunity to double check
it all. Maybe someone does have a definitive source. Ma bell?

- danM
==================


>{Original Message removed}

2000\08\21@144408 by David VanHorn

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>
> >D.C. Line Voltage (Talk Battery) - 48v with receiver on-hook, red wire
> >(ring) negative, 5v for off-hook (with 50-1000 ohm d.c. load on line).

That off-hook number is pure imagination. You can get anything from
near-zero to ???
I've seen 6V to 18V across off-hook equipment. Mostly, it depends on the DC
resistance of the telco line (an unknowable for you) and the instrument
(another unknowable, unless it's your design)

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2000\08\21@151527 by Dan Michaels

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Dave VanHorn wrote:
>>
>> >D.C. Line Voltage (Talk Battery) - 48v with receiver on-hook, red wire
>> >(ring) negative, 5v for off-hook (with 50-1000 ohm d.c. load on line).
>
>That off-hook number is pure imagination. You can get anything from
>near-zero to ???
>I've seen 6V to 18V across off-hook equipment. Mostly, it depends on the DC
>resistance of the telco line (an unknowable for you) and the instrument
>(another unknowable, unless it's your design)
>
>--

These should probably all be checked, if James is gonna cast them
on techref, but I seem to recall 48v was supposed to be the nominal
voltage applied at the telco end - miles of wire away.

- danM

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2000\08\21@152754 by David VanHorn

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>
>These should probably all be checked, if James is gonna cast them
>on techref, but I seem to recall 48v was supposed to be the nominal
>voltage applied at the telco end - miles of wire away.

Even that, I've seen as low as 12V and as high as 52, 24 is not uncommon.
48 is the correct "nominal" number, but the telco may supply other
"nominal" voltages depending on the equipment in use. The on-hook voltage
is almost immune to line length variation though, since almost zero current
is flowing.
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2000\08\21@163435 by Barry Gershenfeld

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>Thanks guys,
>
>Bob just defined my problem. The task is to recognize a busy signal from any
>PBX. It's rather about recognizing a signal with some stable frequency. I
>don't believe someone would be able to whistle into a mike a busy signal
>accurate enough :-).
>
>Igor Pokorny

IMHO if someone tries to imitate a busy signal, and the thing hangs
up on him, so be it!  Seems to me that the criteria for a busy signal
could be pretty loose.  There are only a few things you would normally
get during call progress.  So, sample the amplitude and see if it fits the
following:

Goes on and off (on= > 60% amplitude, off = < 20% amplitude, and
 yes I made those numbers up, use your own)

The repeat rate of the sound is between 3Hz and 1Hz.

The duty cycle on the 'pulses' is the "same" each time you
sample it.  (You decide how close "same" is).

Pretty loose definition, but it ought to work.  The only reason
I'm brave enough to suggest such a thing is that I've owned a
lot of modems over the years and been surprised at how many
different kinds of busy signals they recognize.  Seemed to me
they weren't being too critical about the whole thing.

Think of this: if you had a light instead of a speaker, could
you "spot" the busy signal?

Barry

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2000\08\21@200142 by Bob Ammerman

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----- Original Message -----
From: Dan Michaels <oricomspamspam_OUTLYNX.SNI.NET>
To: <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Monday, August 21, 2000 3:14 PM
Subject: Re: [PIC]: Modulated pulses


> Dave VanHorn wrote:
> >>
> >> >D.C. Line Voltage (Talk Battery) - 48v with receiver on-hook, red wire
> >> >(ring) negative, 5v for off-hook (with 50-1000 ohm d.c. load on line).
> >
> >That off-hook number is pure imagination. You can get anything from
> >near-zero to ???
> >I've seen 6V to 18V across off-hook equipment. Mostly, it depends on the
DC
> >resistance of the telco line (an unknowable for you) and the instrument
> >(another unknowable, unless it's your design)
> >
> >--
>
> These should probably all be checked, if James is gonna cast them
> on techref, but I seem to recall 48v was supposed to be the nominal
> voltage applied at the telco end - miles of wire away.

Yep, and given that the DC resistance of an on-hook phone is nearly infinite
(relative to the wire to the TELCO) you'll see the 48v nominal across the
set.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

>
> - danM
>
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