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Efficient telephone audio (300-650Hz) fedback mechanism !!!

Discussion in 'Audio' started by vinodquilon, Feb 23, 2010.

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  1. vinodquilon

    vinodquilon

    15
    0
    Jan 10, 2010
    Can anybody suggest any efficient audio fed-back mechanism through telephone line
    so that the telephoning person can hear audio beeps, by which he can check the
    status of remotely controlled device (teleremote control).

    I have tried two circuits (see two attached files)


    But cannot hear any sounds at remote calling end. I have tried all frequencies in the range 300-650Hz by varying
    POT in the 555 astable audio beeps generator. But no result.

    I have selected this range as in this range there is no possibility for any DTMF tones.
    Thus audio frequency correctly fed-back to telephone line without detected by DTMF IC.

    Audio beep relay turns on only after off-hook relay get activated.

    I know that, in normal telephone line our vocal audio is captured by Mic, in turn converted
    into AF electrical signals. To check further fed-back mechanism ( & to imitate in my project),
    I opened my telephone set. But nothing can find out on a small, but complex circuit board
    inside the telephone set.

    Does Anyone knows any circuits (that should be of workable) ???

    I forgot to say, I am feeding square pulses of audio frequency.


    [ I SAY SORRY TO ALL FORUM MEMBERS FOR POSTING THREADS ON THE SAME SUBJECT BASED ON TELEPHONE ]https://www.electronicspoint.com/images/smilies/mad.gif
     

    Attached Files:

    Last edited: Feb 23, 2010
  2. vinodquilon

    vinodquilon

    15
    0
    Jan 10, 2010
    I think all these problems can be solved by using RC or wein bridge oscillator
    at audio frequency. Thus replacing square pulses with sine waves.
    10k will be replaced with 470 ohm at coupling path. What about my prediction ???
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    A 0.1uF cap has an impedance of 5305 ohms at 300Hz, then you add a 10k resistor in series with this, resulting in a 11.32k impedance feeding into a 600 ohm line. Only 5% of the voltage you feed in will make it to the line. Telephone systems doesn't have much of a dynamic range so this may very well drown in noise.
    Try replacing the 0.1uFcap with 1uf and the 10k resistor with 470 ohm. This will give an impedance of 708 ohms at 300Hz.
    If you put the resistor first, then the relay and the cap, you can use the resistor as a low-pass filter too - adding a capacitor to ground. Sine is good to avoid interfering overtones.
    Google "telephone patch circuit" to learn more about what you're trying to do here. Many useful examples turn up even in the first 2 hits, with 2 million hits to go.
     
  4. vinodquilon

    vinodquilon

    15
    0
    Jan 10, 2010
    Dear Resqueline,
    Nice explanation. Thanks...
     
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