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how I can connect 89c51serial port to telephone lineto send data?

Discussion in 'Electronic Basics' started by [email protected], May 27, 2007.

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  1. Guest

    dear all,
    I try to send vedio from cctv via telephone line I connect the cctv
    camera output to ADC and the output of the ADC to Atmel 89c51
    micocontroller to send the data serial but I want to connect the
    output of the atmel89c51 to the telephone line

    please help?

    what the next step

    best regards
  2. Jamie

    Jamie Guest

    you need a one to one audio transformer to isolate the
    DC voltage .
    A good pair of clamping diodes to protect the processor
    from the ring voltage.

    Don't expect to send square wave signals directly. you'll have
    to device a method of using sine wave audio.
    this can be done via good voltage comparator on the RX end to
    decode it.
  3. Guest

    first of all many thanks for your reply but I ask for this audio
    transformer I didn't find it in the electronic shop in my village. and
    I have 2 questions here
    -is there is replacement for it with another circuits & if it to
    isolate could I replace it with opticoupller pc817 for example because
    it is available here or optodiac to fire triac gate if it is suitable?

    -for the voltage comparator is it ok (lm393 Low power dual voltage
    comparator )
    and if it is ok what is the reference voltage value I should use?
    ( I measured the telephone line voltage & it about 57volt at rest &
    may be 70-110 at ring (sure I didn't measured the ring voltage)
  4. Bob

    Bob Guest

    Sheesh! The silly gets ridiculous.

    If sending baseband data over a phone line were this easy then the modem
    would never have been invented.

    The maximum bitrate a plain old telephone line will pass, through the public
    switched network, is about 50kbps. Can you limit your video signal to this
    type of bitrate? No, right?

    Your only chance is to store up a bunch of video and then send it
    s-l-o-w-l-y over the phone line (in non- real time) by using a modem. If you
    can send the digitally-encoded video over a DSL or cable modem then you'll
    be able to send it in real time. Otherwise fahgettaboudit.

  5. Don Bowey

    Don Bowey Guest

    You are correct if the intended connection is a dial-up.

    However, the OP has not stated whether it is, or whether it is a
    point-to-point connection, perhaps on non-loaded cable.

    How about it OP? What are you trying to do?

  6. Jamie

    Jamie Guest

    if you want to got that with the isolator that's fine. in your case it
    might just work how ever, you should be using a transistor output type
    that drives a HV transistor with a reverser polarity protection diode.
    I think it would be simpler for a 1:1 transformer..

    For common stores and parts look at Radio shack, I don't know where
    you are from how ever.. take a look here

    You should also have a 120 Volt suppressor on the line side along with
    clamping diodes on the uC side.
    if you only have single project then rip one from an old modem or
    the like.

    If this is going to be a production product then look else where like or for 1:1 isolation signal transformers.
  7. Jasen

    Jasen Guest

    learn about bandwidth.

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