telephone line

hey all,

I want to start playing with the arduino board and the telephone line (without any dtmf module), my question is whether it's ok to connect the 2 telephone wires to the arduino's analog pins (since according to some web pages i found about the phoneline, when the phone rings the lines gets up to 71 volts AC)..

so, is it ok? or do i have to use voltage regulator (and if so, how can i tell if the phone "rings"?)

Thanks in advance, Erez.

No that would be a very bad idea.

Arduinos anlog in can only handle up to 5V and only DC.

So messing with the voltages on the phoneline will require both some kind of rectification and a serious level shifting of the voltage.

Also where i live i don't think it is legal to mess with the phone line, but that may be different in other places.

If you were going to do it (and ignore the law and/or feelings of the phone provider) it would need to be optically isolated from the Arduino. A neon indicator with a suitable resistor may work on the phone side. Then a phototransistor looking at it for the arduino ?

Telephone ringing voltage is about 90V (or higher in places) so hooking your Arduino to this is a very BAD idea.

Telephone line voltage nominally is -48V.

Buying a module is safest way. Finding an older External modem that uses AT commands from a serial connection is safest IMO. That way the modem will detect rings and let you know.

I wouldn't try to mess too much with Arduino and telephone line by itself. I would get a specific module to interface with it. Arduino is not able to do much work on a telephone line: -It can't accept the line voltage (too high) -It can't decode the ringing (again too high) -It will be hard to decode DTMF, and there are modules for this -It hasn't analog output so it cannot apply any wise signal into the line...

As I said, there are specific phone line interfaces which you should try.