DougieLawson wrote:Telephone lines run at 50V AC when the bell rings that should fry your RPi nicely and quickly. Telephone lines are NOT ethernet. Telephone lines are still analog. In many countries it is illegal to connect non-approved equipment to the telco's system (it is in the UK).
To connect one to your RPi you NEED a USB modem.
A modem, yes, but it need not be USB. Modems used to be serial port devices.
If you do it on the GPIO pins there are three problems:
1. GPIO is TTL, RS232 modems are anything from 5V to 26V so you need a MAX3232 chip to convert to TTL.
2. The RPi is pre-configured to have a serial console on the UART pins (for some unknown reason designed to make life unnecessarily difficult)
3. There's no RTS pin on the UART, modems usually need RTS
So using a USB modem (as long as it is NOT a crappy Conexant Winmodem) becomes desirable as it solves those three problems in one hit.