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telephone circuit

Discussion in 'Electronic Basics' started by lerameur, Sep 2, 2008.

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  1. lerameur

    lerameur Guest

    Hello,

    I am using a pic controller for a dialer project. My goal is to dial
    a number, when the receiving end picks up, then send some dtmf tone
    for a few minutes.
    Sounds simple, but I do not know how to tell my controller that the
    receiving end has picked up or not. Right now I just let it ring for
    10 seconds, and send my dial tone after that. I would like it to be
    more 'intelligent' by knowing when the receiver has picked up so I can
    send the dial tone (message),
    thanks

    K
     
  2. lerameur

    lerameur Guest

    Yes but how is this handle in circuitry. I just realize that I cannot
    use the same circuit with audio transformer as I did in DTMF to signal
    out. How should the voltage at the line while dialing? and once the
    party has pick up the phone ?

    Ken
     
  3. ian field

    ian field Guest

    Yes but how is this handle in circuitry. I just realize that I cannot
    use the same circuit with audio transformer as I did in DTMF to signal
    out. How should the voltage at the line while dialing? and once the
    party has pick up the phone ?

    Ken

    Examine an old internal PC modem to see what general components are used,
    the telephone line is energised with about 48V, there are various examples
    of telephone circuitry that can be found with google, often a modem presents
    the AC terminals of a bridge rectifier (W04 etc) the line current is usually
    modulated by a high voltage transistor across the bridge rectifier DC
    terminals.
     
  4. Jasen Betts

    Jasen Betts Guest

    some exchanges will signal when the remote end picks up (and when they
    hang up) by reversing the polarity. if you don't have that you have to
    do what modems do and listen for a signal from the remote end.
    or do what fax machines do and send a tone periodically uitil you get
    a reply.

    Bye.
    Jasen
     
  5. That's always a problem for loop-start lines, which I presume is what
    you have. They're designed for calls placed by humans, to humans,
    rather than machine-to-machine trunks. There isn't any 100% positive
    electrical signal, such as a voltage level, current flow, etc. that's
    transmitted end-to-end & can alert a dumb machine to a distant-end
    answer.

    What's usually used to determine answer is call progress tone
    detection. Call progress tones are the various tones that alert a
    human caller to the status of the call. Common call progress tones
    include dial tone, ring-back, busy, & reorder. All of these tones
    appear within the audio frequency band of the circuit, mostly as pairs
    of frequencies. If you've ever called to or from certain PBXes, or
    various countries, you should have noticed that these tones can vary
    considerably, both in terms of frequency but also cadence. In North
    America, there are standards for the public network, but once you've
    left the public network & connect to a private PBX, you may encounter
    something else entirely. Same for other countries, but with different
    standards. Depending on where you're calling FROM, as well as TO,
    you'll need to be able to reliably detect a variety of call progress
    tones.

    http://en.wikipedia.org/wiki/Precise_Tone_Plan
    http://www.clare.com/home/pdfs.nsf/www/AN-CPTS-R1.pdf/$file/AN-CPTS-R1.pdf
    http://www.3amsystems.com/wireline/tone-search.htm

    JM
     
  6. lerameur

    lerameur Guest

    I have been reading up on them, these are call progress IC .
    They are now next to impossible to get. I guess now they do a DSP
    version so they dont need this hardware.
    Anybody whith an algorithm out there ?

    K
     
  7. lerameur

    lerameur Guest


    well that was before I knew that Central office sends out different
    frequency on the status the phone of the receiver.
    I will look for those frequencies now.
    440Hz and 480Hz means that is it ringing, if it stops, then I suppose
    some pickup at the other end, Then I can program the controller to
    send my signal.

    K
     
  8. lerameur

    lerameur Guest

    Well lets say I am at work, and my alarm system goes off, it will
    trigger the dialer. First, I will see on my phone that someone is
    calling me from home from the call display. Then if I hear a
    continuous dial tone for 20 seconds, then I will know my alarm is on.

    K
     
  9. Ross Herbert

    Ross Herbert Guest

    :
    :Well lets say I am at work, and my alarm system goes off, it will
    :trigger the dialer. First, I will see on my phone that someone is
    :calling me from home from the call display. Then if I hear a
    :continuous dial tone for 20 seconds, then I will know my alarm is on.
    :
    :K


    You've lost me....

    Your alarm at home triggers and dials your work number. You see on your CLI
    display at work that the calling number is your home. Then you hear 20 seconds
    of dial tone so you will know your alarm is "ON"....??????? (scratches head in
    wonderment).

    BTW, don't you mean, "you will know your home alarm has been triggered"?

    Where is the 20 seconds of dial tone coming from? And why dial tone?

    I suggest you start out with something like this project and refine it if
    necessary.
    http://users.tpg.com.au/users/talking/DialAlarm-1-Page1.html
     
  10. Ross Herbert

    Ross Herbert Guest

    :On Fri, 05 Sep 2008 02:02:12 GMT, Ross Herbert
    :
    :>:
    :>:Well lets say I am at work, and my alarm system goes off, it will
    :>:trigger the dialer. First, I will see on my phone that someone is
    :>:calling me from home from the call display. Then if I hear a
    :>:continuous dial tone for 20 seconds, then I will know my alarm is on.
    :>:
    :>:K
    :>
    :>
    :>You've lost me....
    :>
    :>Your alarm at home triggers and dials your work number. You see on your CLI
    :>display at work that the calling number is your home. Then you hear 20 seconds
    :>of dial tone so you will know your alarm is "ON"....??????? (scratches head in
    :>wonderment).
    :>
    :>BTW, don't you mean, "you will know your home alarm has been triggered"?
    :>
    :>Where is the 20 seconds of dial tone coming from? And why dial tone?
    :>
    :>I suggest you start out with something like this project and refine it if
    :>necessary.
    :>http://users.tpg.com.au/users/talking/DialAlarm-1-Page1.html
    :
    :Haven't looked at your link yet, but this is an easy one. Since the
    :human is in control of the situation on the receive end, answer the
    :phone and press #99 or some other acknowledging code, and the
    :auto-dialer can respond in whatever way it's been programmed. A whole
    :series of DTMF communication may be programmed, depending on the
    :sophistication of the auto-dialer apparatus.
    :
    :Of course, the assumption remains that the receiving human knows that
    :the alarm has triggered from the mere fact that home is calling, and
    :presumably is not the wife asking to have a loaf of bread or jar of
    :pickles picked up on the way home. Unless there is something
    :tangible that gives value to the receiver communicating with the
    :auto-dialer, there is no need for anything more than caller-ID at the
    :receiving end.


    I know the human at the receive end controls the situation and that he can
    respond to the call using dtmf. But when he does this why would the sending end
    respond with dial tone? This would require the generation of 2 tones which are
    not part of the dtmf frequency plan. Ok, not hard to do in software, but it
    seems unneccesary. Why not respond with one of the standard dtmf tones instead
    of dial tone?

    Out here dial tone is 400Hz + 425Hz afaik.
     
  11. lerameur

    lerameur Guest

    After reading on the subject I realize that the Central office sends
    out signals about state of the connection (ringing, busy). I am going
    to get a transceiver chip so I can dial out and get the signals, I
    think the MTC888 should be good for this.
    K
     
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