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PICList Thread
'Telephone ring detector'
1996\03\12@164142 by Thanasis Stefanopoulos

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Hello to all the PICers,

I am developing a project for my Univercity and a part of my circuit is the
telephone ring detector. The circuits I have tried didn't work properly.
The operation of the detector is: The input is the telephone line and the
output
goes to a port-pin of the PIC. The input is optically isolated with the
output. When
the phone rings the output must have a logic 0 (0V) and when it doesn't ring
it must
have a logic 1 (5V).
My problem is that when the phone was ringing the output dropped only at
2.5Volts
and not below the 1Volt.
I would like to suggest me more circuits that do this detection, or give me
any kind of
information to help me.

The circuit I tried:                                              o+5v
                3.3K                270                             \
 o--| |------/\/\/\/\----------/\/\/\/\/\---------                / 10K
      470pF             |                           |                |
                             |                           |                |
--------------o  output
Line                       _/                         \/   --->    |/
       Zener4.7V    /                             _  --->    |\
                            /\                           |                |
                            |                            |                |
 o--||----------------------------------------                _  0V
                                                                          -


Thank for reading my problem,
Thanassis Stefanopoulos

email: spam_OUTthastef80345TakeThisOuTspamhol.gr

1996\03\12@172806 by Mike Riendeau

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  Thanasis,

  Although I could not decipher your circuit,
  I think you may have trouble rectifying the
  AC ring signal.  I'm no telecom expert, but
  the following circuit might help you:

                               +5V     +5V
                                ^       ^
                                |       |
                                >      ---
                                > 47K  --- 0.1uF
                                >       |
                                |       |
                                |-----------> To
                                |             PIC
                                >
                                > 2.2K
       0.47uF                   >
               4.7K             |
         ||                     |
  Tip >--||---^^^^v---v         |
         ||    1  |   |         | 4
                 _|_ ###      | /
                 \ / / \ -->  |/
                 ### ---      |
               2  |   |       |\
  Ring <----------v---v         V 3
                                |
                AC input opto   |
                               ---
                NEC PS2701-1    -  GND

 All parts are available from Digi-Key.

                               Good luck,
                                  Mike

1996\03\12@175223 by Scott Dattalo

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Thanasis,

I couldn't make out your circuit either. But rather than
try to explain or decipher what you have got, I can point you to:

ftp://ftp.ee.ualberta.ca/pub/cookbook/telecom/

or its mirror:

file://wattson.ee.ualberta.ca/pub/cookbook/telecom/

There you will find a "Phone in Use Circuit", which is similar (I think)
to what you want to do.


Scott

1996\03\13@070508 by Liu, Zemin

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Thanassis Stefanopoulos,

Your circuit don't display properly in my screen, so I cannot get what you
really have tried. I have some experience on this subject myself. Maybe you
can try the scheme below.  The important thing is you should choose the
values of C, R1 and opto coupler according to the specifications of your
phone line( especially its ring voltage). Choose C and R1 to enable the
coupler be drived sufficiently.

In our country, I use C = 1uF/400V, R = 50K ~ 100K, and 4N26 or 4N30 coupler.
D is for protection, I use 1N4007.

Hope this helps.

Zemin Liu
.....isslzmKILLspamspam@spam@zsulink.zsu.edu.cn



                                     +5V
                                    |
                                    > R2
                                    <
                          opto      |
        C    R1           coupler   |
 ------| |--/\/\/--|-----|     /----|-------------- Output
                   |     |   |/
                   --   \/   |
 phone line        /\   --   |\
                D  |     |   | \
                   |     |      V
 ------------------|-----|      |------------------ GND
{Quote hidden}

1996\03\13@071349 by Andy Errington

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I don't know about other countries, but here in the UK one is expressly
forbidden to connect non-approved (e.g. home-made) equipment to the
telephone system.  To detect a phone ringing I would by a plug-in telephone
ringer (approved) with an LED, and use a photodetector to detect the LED
flashing.  On the other hand I don't know any of the PTTs can tell you are
using non-approved equipment...

Andy

--
---------------------------------------------------------------------
Andrew M Errington                               Tel: +44 1524 593678
Microcomputer Consultant                         Fax: +44 1524 844011
Lancaster University                      .....a.erringtonKILLspamspam.....lancaster.ac.uk
Lancaster LA1 4YW     www.lancs.ac.uk/people/cpaame/cpaame.htm
---------------------------------------------------------------------

>

1996\03\13@123849 by Kalle Pihlajasaari

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> output. When
> the phone rings the output must have a logic 0 (0V) and when it doesn't ring
> it must
> have a logic 1 (5V).
> My problem is that when the phone was ringing the output dropped only at
> 2.5Volts
> and not below the 1Volt.

The Ring signal is AC at 17 .. 25 Hz and the average of a half wave
rectified signal at 5V will be about 2.5V.

You can place a cap across the photo transistor to hold the level
for the off half cycle or place a bridge rectifier BETWEEN the ring
capacitor and the optoisolator.

Cheers
--
Kalle Pihlajasaari     EraseMEkallespam_OUTspamTakeThisOuTdata.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751

1996\03\13@133930 by mike
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In message <826719287.20137.0spamspam_OUTvms.dc.lsoft.com> @spam@PICLISTKILLspamspamMITVMA.MIT.EDU writes:
> I don't know about other countries, but here in the UK one is expressly
> forbidden to connect non-approved (e.g. home-made) equipment to the
> telephone system.
[snip]

Okay, so how would someone who wanted to do this legally and have it
approved by BABT do this?

Regards,


Mike

1996\03\14@020204 by f-L. Troska

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>> ...  When the phone rings the output must have a logic 0 (0V) and when it
doesn't ring
>> it must  have a logic 1 (5V).
>> My problem is that when the phone was ringing the output dropped only at
>> 2.5Volts and not below the 1Volt.

Kalle Pihlajasaari     (KILLspamkalleKILLspamspamdata.co.za) wrote:

>The Ring signal is AC at 17 .. 25 Hz and the average of a half wave
>rectified signal at 5V will be about 2.5V.

The actual frequency varies from country to country...
 ... and is in the range of  45 .. 100 (..120) V AC at the a-, b- phone lines.
 AC ring voltage too varies as above ...
( Example: German Telecom: 23 .. 54Hz @ 45 .. 75 V/AC for ring detect )

I propose two(!) z-diodes with (e.g.) their anodes back to back at a
row with the RC-combination; thus give protection to the optocoupler and
limiting the  input voltage.

Keep in mind, that this circuitry is broadband.
Frequence detection, duration and pause times should be done by the
PIC !

As some others posted: you are not allowed to connect this equipment to the
public telephone system   --  to a PBX ... of course you can.

(for more information have a look at the ITU recommendations
and the technical infos of the PTT in your country.)

Regards Ralf.

1996\03\14@031624 by f-L. Troska

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>The Ring signal is AC at 17 .. 25 Hz and the average of a half wave
>rectified signal at 5V will be about 2.5V.

IMHO: No.
It's because the opto's output / the transistor is switched with this
low frequency, thus giving an average of 2.5V ...

Take a voltmeter & you get at the transistors output:
 a) needle type   -->  2.5V reading
 b) digital type  --> 'fluctuating' reading

 c) take an osci. -->  you'll see the ring signal at full (or half )
                       frequency  _but_  'clipped' to 5V peak-peak !!


>You can place a cap across the photo transistor to hold the level
>for the off half cycle or place a bridge rectifier BETWEEN the ring
>capacitor and the optoisolator.


A capac. at the opto's output(!) will not be the solution (in a general
application), so you have to check at this point of the circuitry for
the correct frequ. range (!) of the ring signal.


>Cheers

.. to you too

Ralf.

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