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Telephone line audio interface to PC

Discussion in 'Electronic Design' started by Country Loon, Oct 24, 2004.

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  1. Country Loon

    Country Loon Guest

    I want my PC to interface to the telephone line and was wondering about the
    problems. I know how to interface the audio via an ac coupled 1:1 isolation
    transformer and a diode limiter to prevent the ringer ac voltage from
    damaging the sound card. How do I do the off the hook connection and the
    audio output from the PC feeds where ? How do I accept a call etc

    Thanks

    Tom
     
  2. Rich Grise

    Rich Grise Guest

    Go buy a "voicemodem".

    Have Fun!
    Rich
     
  3. Mac

    Mac Guest

    If you are in the US, there is approximately 50 VDC across the two lines
    that make up your telephone. If you draw a certain amount of DC current
    from that 50 VDC, it will bring down the Voltage, and it will cause the
    central office to consider your telephone "off the hook."

    You can do this by switching in a resistor of the correct value, I guess.
    Or applying a dead short, but that might make it hard to pick up the audio.

    I don't know much about telephones. Hopefully someone will fill in more of
    the details.

    I wonder, would you need to worry about high power line transients and
    lighting and so on? It would be a shame if your computer was completely
    destroyed by a lighting strike miles away from your house.

    And it would be even more of a shame if your house burned down
    altogether.

    --Mac
     
  4. Country Loon

    Country Loon Guest

    I have heard the quality is not as good.

    Tom
     
  5. Country Loon

    Country Loon Guest

    I found this
    http://www.colinfahey.com/2003may_phone_interface/2003may_phone_interface.ht
    m
    http://www.hut.fi/Misc/Electronics/circuits/teleinterface.html


    and other page that explained about the surge voltage protection.

    Tom
     
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