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'Phone Interface'
1996\10\06@082229 by Ricardo Barbosa

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Hi Folks

I need a code (PIC16c54) for an dialer (pulse) and detect line tone.
Can someone help me ? Thanks
Ricardo

       +-------+       +---------+
       | Trafo |       |    P    |
       | 1:1   |-------|    I    |---------- relay (phone line)
       | 600R  |       |    C    |
       +-------+       |    1    |
                       |    6    |---------- relay (phone line dialer)
                       |    C    |
                       |    5    |---------- SET dialer (start)
                       |    4    |---------- RESET dialer (stop)
                       +---------+


'phone interface'
1997\02\03@095801 by Clewer,Brian
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Hi all,
    I am making a project which will ring me up if a certain condition is
met.  My problem is, how do you tell (electronically) when someone picks up
the phone at the other end after placing a call?
Thanks for any info,
Brian.

1997\02\03@102956 by John Payson

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>      I am making a project which will ring me up if a certain condition is
> met.  My problem is, how do you tell (electronically) when someone picks up
> the phone at the other end after placing a call?
> Thanks for any info,

In the U.S., a normal telephone line will not return answer supervision; to
tell when a call is answered, you must listen to what you're getting on the
audio path.  If you hear ringing followed by voice, it was probably answered
(though you may have gotten a "Sorry, all circuits are busy" message).  If
you hear busy signal or continuous ringing, then the call was not answered.

1997\02\03@115518 by Christopher Zguris

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At 02:55 PM 2/3/97 PST, Clewer,Brian wrote:
>Hi all,
>     I am making a project which will ring me up if a certain condition is
>met.  My problem is, how do you tell (electronically) when someone picks up
>the phone at the other end after placing a call?
>Thanks for any info,
>Brian.
>
>

The way I detected something similar was to hook up a line sense relay
between the line and the load (phone, phone line interface etc.). I know a
hangup at the other end causes the relay to deenergize for a fraction of a
sec (.25, maybe?). Not sure if it does the same for a pickup at the other
end, never tested for that.

Chris

   ======================================================================
         Christopher Zguris  -  spam_OUTczgurisTakeThisOuTspaminterport.net  -  Uhhh, Ear?
                     1991 VFR 750 (with aspalt detailing)
                             IVFROC, HSTA, HRCA

                              RUSSIAN COMMUNISM
                              =================
    You have two cows.  You have to take care of them, but the government
                             takes all the milk.

   ======================================================================

1997\02\03@124300 by engmessi

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How about detect when the ringing signal stops ?


>At 02:55 PM 2/3/97 PST, Clewer,Brian wrote:
>>Hi all,
>>     I am making a project which will ring me up if a certain condition is
>>met.  My problem is, how do you tell (electronically) when someone picks up
>>the phone at the other end after placing a call?
>>Thanks for any info,
>>Brian.

1997\02\03@143933 by Tim Kerby

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What about a line voltage change.  Judging by British systems this is the
standard:
Ring is on audio in line and is capacitive coupled to bell line
When the phone is picked up, BT must know when and thus sense a line voltage
change.

Tim


At 15:42 03/02/97 -0200, you wrote:
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1997\02\03@170619 by TONY NIXON 54964

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>     I am making a project which will ring me up if a certain condition is
>met.  My problem is, how do you tell (electronically) when someone picks up
>the phone at the other end after placing a call?
>Thanks for any info,
>Brian.

I once constructed an alarm system that interfaced to the phone line
via a relay and isolation transformer if it triggerred.

A simple high gain amplifier was used in conjunction with a
comparator to 'sense' the signals on the phone line. Any time a
signal was present on the line the comparator output would go high.

If this high was continuous I would assume that Dial Tone was present
and I could begin dialling a number.

Busy Tone, Ring Tone, Number Unobtainable, etc., all have set bursts
of tone which can also be detected in this manner. I have never tried
it but I would think that if the signal from the comparator was
erratic, then you could assume 'talking' on the other end.

Note that in Australia there are some stringent laws that prohibit
any such devices to be connected to phone lines unless approved by
the appropriate authority. With good reason too. Safety to equipment
and more importantly - personnel.

Regards
Tony


Just when I thought I knew it all,
I learned that I didn't.

1997\02\03@171027 by Andrew Warren

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Clewer,Brian <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU> wrote:

> I am making a project which will ring me up if a certain condition
> is met.  My problem is, how do you tell (electronically) when
> someone picks up the phone at the other end after placing a call?

Here in the States, you have to listen to the audio.  With
trial-and-error, you should be able to train your PIC to recognize
the difference between rings, busy signals, and voice.

-Andy

Andrew Warren - fastfwdspamKILLspamix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1997\02\03@180236 by Lee Jones

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>>> I am making a project which will ring me up if a certain condition
>>> is met.  My problem is, how do you tell (electronically) when someone
>>> picks up the phone at the other end after placing a call?

>> How about detect when the ringing signal stops ?

> What about a line voltage change.  Judging by British systems
> this is the standard: Ring is on audio in line and is capacitive
> coupled to bell line.  When the phone is picked up, BT must know
> when and thus sense a line voltage change.

Without the details, that essentially how it works in the US too.
Ring is 20Hz'ish 95VAC signal coupled to ringer.

However, the central office (aka CO) has a real advantage in
telling when the remote phone instrument is "picked up".  The
CO provides 48VDC potential across the phone line (1 pair).*

When the phone instrument goes off hook, a set of contacts
close and place a resistance across the line.  This causes
a current to flow.  Depending on rural versus metropolitan
conditions, distance from the CO, and phone instrument, the
current flow is 20mA to 60mA.

When you are placing a call, the situation is reversed.  The
CO sees you go off-hook (current starts flowing) on an idle
line, so it assignes you to a digit collector and gives you
dialtone.  The current flows continuously during your call.
When the current flow stops, the CO assumes you've hung up.

If answer supervision is available and active on your line,
the information on the called party answering (i.e. going
off-hook) is commonly passed back as a voltage reversal.
In other words, the 48VDC potential supplied to you by the
CO will invert polarity; sometimes only for a short period
of time.

There are standards in this area.  There's also lots of
variability depending on the carrier (operating company
in the US) and/or the equipment installed at the CO.

                                               Lee Jones

* My discussion is restricted to analog POTS (plain old
 telephone service) lines.

-------------------------------------------------------------------
Jones Computer Communications             .....leeKILLspamspam.....frumble.claremont.edu
509 Black Hills Dr, Claremont, CA 91711         voice: 909-621-9008
-------------------------------------------------------------------

1997\02\03@185628 by Christopher Zguris

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At 01:02 PM 2/3/97 -0800, Andrew Warren wrote:
>Clewer,Brian <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU> wrote:
>
>> I am making a project which will ring me up if a certain condition
>> is met.  My problem is, how do you tell (electronically) when
>> someone picks up the phone at the other end after placing a call?
>
>Here in the States, you have to listen to the audio.  With
>trial-and-error, you should be able to train your PIC to recognize
>the difference between rings, busy signals, and voice.
>

If all you want to do is decode progress tones (busy, ringing, fast-busy,
dial-tone), Teltone makes a progress tone decoder IC that has 4 outputs plus
a strobe (total 5 lines). It is fairly speech immune, and designed for
commercial telecom devices. Price was ~$12 ea last time I bought some. They
also make a cheaper decoder that is not as easy to use, I have no experience
with it.

>-Andy
>
>Andrew Warren - fastfwdspamspam_OUTix.netcom.com
>Fast Forward Engineering, Vista, California
>http://www.geocities.com/SiliconValley/2499
>
>

Chris

   ======================================================================
         Christopher Zguris  -  @spam@czgurisKILLspamspaminterport.net  -  Uhhh, Ear?
                     1991 VFR 750 (with aspalt detailing)
                             IVFROC, HSTA, HRCA

                              RUSSIAN COMMUNISM
                              =================
    You have two cows.  You have to take care of them, but the government
                             takes all the milk.

   ======================================================================

1997\02\03@191100 by Glenn Johansson

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part 0 559 bytes
On the side with the RINGING telephone, the polarity switches when the hook is lifted (besides, the ringing in a phone with a bell is caused by switching polarity fast). A hook-lift is signalled by changing the impedance.

On the CALLER side, there is no simple way of telling whether the recipient picked up the phone or not. My ZyXEL voice modems resorts to a "ringback goes away" timer for this (which by the way doesn't work, and nobody at ZyXEL ever answer my faxes).

Regards,
Glenn
SATELLITE HACK SERVICES
http://www.tripnet.se/~glenn/s.htm

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