I have an analog phone (specifically a Spirit of St. Louis Field Phone Mark I). I am thinking of a project where instead of connecting it to a land line, I connect the phone to a Raspberry Pi and read and control it from there. Note I don't want to make actual calls with the phone, just receive the phone input (dial numbers, sound, ..?) on the RPI, and send output (sound, ..?) from the RPI to the phone.

However I don't know much about phones and am looking for some tips. The phone has an RJ11 jack that is supposed to be connected to a land line, and no other jacks. Evidently the phone has to get power through the jack, too.

I found some USB-to-RJ11 cables that should be able to connect to phones, but because of USB's low voltage these wouldn't work with a phone that also needs power though the RJ11 jack.

So I think a setup like the following is required.

RPI  <- USB ->  some hardware component  <- RJ11 ->  phone
 ^                       ^
 |                       |
 5V power supply         higher voltage power supply

However I have not yet been able to find the right hardware component.

Am I on the right track? What hardware do I need? Any input is appreciated!

  • Have you reviewed the basic requirements for powering an analog phone line? Like looking at this: hermonlabs.com/products/innerData/pdf/…
    – SDsolar
    May 1, 2017 at 1:37
  • Here is another article from a company that connects phone lines to radio stations for call-in shows. It is technical enough to give some idea of what you are facing: jkaudio.com/article_10.htm
    – SDsolar
    May 1, 2017 at 1:38
  • Thanks for your comments, I have a better idea of what I'm looking at thanks to those links. However, they are very low level and I'm not looking to create my own hardware to deal with the signals. I am looking for something ready-made that I can use to communicate digitally with the analog phone. I am now thinking a product like this might be of use. However even if this can interface successfully with the phone, I am not sure how to then communicate with the product from my RPI. It would also take up my Ethernet port. Do you have any feedback?
    – user66431
    May 5, 2017 at 14:55

1 Answer 1


I have ordered a Linksys PAP2T device and connected it to my computer (not RPI yet) on one end and the analog phone on the other end. Using a SIP protocol library (sipsimple) I am able to receive and place calls to/from either end. On the computer end I can also capture the audio from the phone, receive DTMF digits and stream audio files to the phone. Configuration of the device was straight-forward.

Although the device seems somewhat overkill since it has a lot of features that I don't need, it does allow me to do exactly what I want without too much fuss!

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