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

[vinodquilon]

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) ???




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[FvM]

Feeding the tones through 10K series resistor to a 600 ohm line doesn't result in a very high sound level...

I don't understand the considerations about possible DTMF interferences. As the "D" clarifies, a single tone won't never be understood as a dialing tone.

 

[vinodquilon]

Re: Efficient telephone audio (300-650Hz) fedback mechanism

Feeding the tones through 10K series resistor to a 600 ohm line doesn't result in a very high sound level...

I directly fed without 10 k (as beep feed only after off-hook), but nothing works.
I forgot to say, I am feeding square pulses of audio frequency.

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 ???

 

[FvM]

Re: Efficient telephone audio (300-650Hz) fedback mechanism

If the oscillator is working and relays closed, it's impossible that you don't hear it. Square wave would have even a higher
subjective loudness because of the harmonics. There must be a different, very basic problem.

P.S.: I see, that the circuit shown above never goes off-hook, because the DC path is blocked by capacitor C4. That's strange,
you presented an operational line interface in a previous threads.

 

[vinodquilon]

Re: Efficient telephone audio (300-650Hz) fedback mechanism

P.S.: I see, that the circuit shown above never goes off-hook, because the DC path is blocked by capacitor C4. That's strange,
you presented an operational line interface in a previous threads.[/quote]


Ya, the circuit doesn't go to off-hook. But I am using OEP1200 1:1 TRANSFORMER.
There is a specification in the data sheet as "Do not pass DC current through windings". In the former one parallel resistor across capacitor would allow DC flow.

What is the solution ???

Added after 26 minutes:



P.S.: I see, that the circuit shown above never goes off-hook, because the DC path is blocked by capacitor C4. That's strange,
you presented an operational line interface in a previous threads.[/quote]

See the file fedback2(11).pdf
In that, I will disconnect the relay end of R6 and connect it at the Ring arrow
end. Thus transformer lower end directly connect to relay and one R6 junction point.
That way R6 resistor will loop the line (when relay turns on), and capacitively isolate the transformer.

Now there exists a DC load to loop the line. Does it works ???

Thanks to rogs.