I am curious how to interface with a phone line. (in US) I would like to just get audio out of it, and if possible dial numbers. now I did do research and found there is 40-70 volts going through there, how could I safely lower the voltage to say 5 volts? could I just use a resistor or will it fry?
I did a ringer detector using an opto-coupler. The telephone circuit have to be a certain design to : 1. Not overload the phone line. 2. Use safety parts. → fuse and Varactor ← for high voltage protection.
3. did you took apart a phone ? And electronics phone ? or an old modem ?
4. Get a schematic of a old modem.
The phone line do normaly have 2 type of voltage. DC and AC. DC at -48 V off hook and -5 on-hook. and 90 V ac when it ring.
Do some reseach and measured the voltage of your phone line at home using a DVM.
I live in Canada. Our system is the same in the US. We share the same telephone standard. Beside, Alexander Graham Bell invented the phone in Canada, BTW.
Just google : Telephone Interface Circuit and surf the web.
Proper interfacing to phone lines normal involves using an approved DAA module (data access arrangement). These sometimes show up on E-bay or just search with google. It will handles all the voltage isolation issues and insures you won't have someone knocking on your door from the phone company when you ground out one of the phone wires or send to 'hot' a signal out onto the line.
It will handle all the voltage isolation issues and insure you won't have someone knocking on your door from the phone company when you ground out one of the phone wires or or send to 'hot' a signal out onto the line.
Or worst... the feds... ]:)