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Telephone line to Audio Interface

Discussion in 'General Electronics' started by Eduardo Fonseca Brasil, Apr 16, 2004.

  1. Hello,

    I need to build some hardware that will be connected to a regular
    phone line and to the input and output of my sound card.

    I want to be able to send sound from my computer to the phone line,
    and from the phone line to my computer.

    I've searched google, and found this site:
    http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html

    It has lots of phone line interfaces, but i don't know which one i
    should use. I don't even know if any of the interfaces from this site
    will work.
    Some of the interfaces only sends audio in one way (telephone line ->
    computer), but i wanted one that could send the audio both ways.

    Anyone ever done something like this?
    Is this easy/possible to do?

    Anyone could help me? (Maybe some other site, some successful
    experience or some documentation)

    Thanks in advance (and sorry about my bad english)
    Eduardo
     
  2. Karl Uppiano

    Karl Uppiano Guest

    Your best bet might be to use a voice/modem
    http://www.modemsite.com/56k/voice.asp. These modems are set up to interface
    audio to phone lines. The work with your sound card to separate the send and
    receive audio for you with minimal feedback. This would eliminate the need
    for an external interface. You can just plug your phone line into your
    computer.
     
  3. Seth Koster

    Seth Koster Guest

    Anyone ever done something like this?
    The absolute easiest way I can think of is to plug a microphone
    into the mic input of your sound card and tape it to the earpiece of
    the phone and to plug a speaker into the speaker output of your sound
    card and tape that to the mouthpiece of your phone. This also
    isolates the phone from the computer for safety.
    My cordless phone has a jack to accept a handsfree headset, you
    might be able to wire the sound card output and input to a cord which
    plugs into the jack if there is one on your phone.
    The question is what does the phone expect as input and what does
    it send as output, and what does the sound card expect as an input and
    send as an output. I don't know and without this info I'd be leery
    of wiring my expensive computer to a phone. Maybe someone else here
    has more knowledge of phones and computers and could help more.
    I never even considered doing this, so I have no experience.

    Your welcome and your english seems fine to me.
     
  4. Dbowey

    Dbowey Guest

    Eduardo posted:

    <<
    I need to build some hardware that will be connected to a regular
    phone line and to the input and output of my sound card.

    I want to be able to send sound from my computer to the phone line,
    and from the phone line to my computer.

    I've searched google, and found this site:
    http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html

    It has lots of phone line interfaces, but i don't know which one i
    should use. I don't even know if any of the interfaces from this site
    will work.
    Some of the interfaces only sends audio in one way (telephone line ->
    computer), but i wanted one that could send the audio both ways.

    Anyone ever done something like this?
    Is this easy/possible to do?

    Anyone could help me? (Maybe some other site, some successful
    experience or some documentation)
    You should use the one titled "Telecom hybrid circuits for other equipments
    than telephones

    Traditional transformer hybrid circuit"


    Most telephone lines are not 600 Ohms, however, so you should use a 900 Ohm
    resistor in series with about a 2 mFd capacitor as RB.

    The 111C transformers (Repeat coils in Telco parlance) may be available on
    eBay, but if not, any good (lots of iron) 1:1 transformer will do the job. You
    need two identical transformers.

    Don
     
  5. Externet

    Externet Guest

    Hello Eduardo.

    The correct way to interface a telephone line is with ANY audio output
    transformer. Those tiny ones canibalized from old transistor radios
    work fine.
    Connect the low impedance secondary ~8 Ohm IN SERIES TO ONE of the
    telephone line conductors.
    The primary will be a two-way audio path for any use, cannot be
    detected, can be left permanently connected, and will not be damaged
    with ring signals.
    For protection and clipping, install 2 diodes in inverse parallel to
    the transformer secondary. That will limit audio to 0.7V pp

    Your english is better than many yankee's

    Miguel
     
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