SparkFun Forums

[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)
http://www.scribd.com/doc/27346744
http://www.scribd.com/doc/27346875

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 ]javascript:emoticon(':oops:')

[groggory]

There's more to phones than just putting some voltage and a signal on the lines.

http://www.epanorama.net/circuits/teleinterface.html

Read that and design a circuit from there. I don't have a circuit for you, but getting a deeper understanding of how phones really work would be a good start for you I think.

[vinodquilon]

There's more to phones than just putting some voltage and a signal on the lines.

http://www.epanorama.net/circuits/teleinterface.html

Read that and design a circuit from there. I don't have a circuit for you, but getting a deeper understanding of how phones really work would be a good start for you I think.

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 ???

[riden]

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 ???

Won't make a difference. The problem isn't sine versus square. It is a coupling issue. Most telephone interfaces use a 600 ohm isolation transformer. Look at the links groggory gave you to learn how these interfaces work. Otherwise you will get very frustrated very quickly. And don't forget that most telephone lines have 48v DC or so (depending on the country) on-hook voltage and a 90v AC ringing voltage. That comes to a surprise to some people when they shock themselves.

BTW, you need to be very careful because many countries tightly control what type of devices can be placed on the telco circuits. A poorly designed circuit could disable your phone service and bring the wrath of the phone company down on you. Be careful.

[vinodquilon]

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 ???

Won't make a difference. The problem isn't sine versus square. It is a coupling issue. Most telephone interfaces use a 600 ohm isolation transformer. Look at the links groggory gave you to learn how these interfaces work. Otherwise you will get very frustrated very quickly. And don't forget that most telephone lines have 48v DC or so (depending on the country) on-hook voltage and a 90v AC ringing voltage. That comes to a surprise to some people when they shock themselves.

BTW, you need to be very careful because many countries tightly control what type of devices can be placed on the telco circuits. A poorly designed circuit could disable your phone service and bring the wrath of the phone company down on you. Be careful.

Thank you riden,
I will be careful about all these hazards.