¶ Plain Old Telephone Service (POTS)
Some notes
¶ Voltages and line states
- IDLE - ~48V DC
- RINGING - ~75V AC (ish, just flip the polarity 30hz)
- ACTIVE CALL - ~7V (depends on line length)
¶ Subscriber Line Interface Circuit (SLIC) Module
KS0835F is a nice all in one modules that can generate all the required voltages.
Just hook one end to the phone line and provide 3-5V to the other end.
All the other pins are TTL logic and just analog audio I/O.
¶ Telekom RWT
Landline Phone made in USSR Poland 2nd Week 1985
It uses WT-4 Socket with this pinout.
You can just connect the audio and ringer pins together as Tip wire and use common as Ring wire.
¶ Signaling
Modern phones use DTMF to call numbers instead of pulse dialing
Fax and Modems also need Call-progress tones that are generated
by phone exchange (or in my case a MCU connected to SLIC module)