Use a raspberry pi as a POTS phone?

Question

I would like to use a computer as a handset POTS telephone.

Why? - I want to use a raspberry pi on the telephone port of an Analog Telephone Adapter (ATA) just to see if I can use it to automate telephone calls through the POTS port.

Again, why? - the ObiHai ATAs are the only devices not owned by Google allowed to connect to the Google Voice SIP service directly. I want to see if I can make simple bot-calls to US Phone Numbers or custom voicemail handling for no other reason than curiosity.

How do I connect a computer to a POTS jack to use it as a handset?

Answer 1

Technically, it should be possible, but it would not be easy. It would require additional electrical design and electronics, as well as programming.

POTS lines are analog. The Raspberry Pi's GPIO pins are all digital. You would need to use an analog to digital converter, or create one yourself. Here is some info.

The second problem is POTS electrical power. On a standard Raspberry Pi, all the GPIO pins are 3.3 volts. I believe it is stated that even inputting 5 volts can cause potential damage to the Pi. POTS lines can be as low at 6 volts and spike up to 90 volts. You would need electronics to reduce the power to 3.3 volts coming in and increase it going out. Otherwise, you would fry your Pi. Here is some info on POTS power.

Assuming you could manage to do all of the above, you would need to convert digital data into analog tones that a phone actually uses. You would need to recreate DTMF tones for dialing. You would also need to convert digital audio out to analog and vice versa.

Then there is the programming to manage any of the mentioned processes if they arent handled by the electronics.

Again, its possible, but probably not worth the hassle. A dedicated device seems like a much better solution.

Answer 2

You can't (easily). An ATA is an analog device, and a Pi is digital. You might be able to build some kind of converter for it, (which would be very hard to get right ) but then you may as well just buy additional hardware to Interface with the ATA.

There are really 2 kinds of ATA - an FXS device which allows you to plug a handset into a digital(VoIP) system and an FXO which does the opposite. You can thus probably mate your ObiHai (which sounds like an fxs) device with an FXO device and then use something like Asterisk/FreePBX from your Pi to drive it. Note that you may have to iron out impedance / echo issues.

(Btw, I believe you have used the term POTS incorrectly as you are not connecting to the "plain old telephone network" and the ATA is not an FXO device)