How to transmit the hook state of the rotary phone to a smartphone via the RJ11 socket ?

[phonemaster]

Hello, I would like to restore an old rotary phone with a broken handset to make it a gest book audio recorder, to leave audio messages. The handset no longer works and I have an old smartphone that I could use with a working handset plugged into the jack. I can use a script on my android smartphone to play audio welcome file and then record the person's message but I would like the start and end of this script to be synchronized with the hook state of the rotary phone. eg when the phone is picked up the script starts, when the phone is hung up the script terminate and the audio message is saved on the smartphone.

I think this state is accessible from the rj11 port of the rotary phone but I don't have the slightest idea how to get it and transmit it to the smartphone.

here is a picture

[alto777]

The RJ11 ends up connecting two wires to the telephone.

When you lift up the handset, the resistance between those two wires drops to 200 ohms. That's plenty low enough to pull down an Arduino input in INOUT_PULLUP mode.

If you are literally making no other use of the RJ11 wires, you can treat it like a switch.

Entering digits on the rotary switch ("dialing") will look like rapid on-hook off-hook transitions, so plan on that if you gonna be playing with that part of the real telephone for some reason.

a7

[phonemaster]

That's plenty low enough to pull down an Arduino input in INOUT_PULLUP mode.

so if I understand correctly, I should strip these two wires but next how can I send the signal to the smartphone? (I think you understood that I am a real noob). THANKS

[jremington]

WiFi or Bluetooth would be options. There are plenty of Arduino tutorials on line describing how to send sensor data to smart phones.

None of these are beginner projects, in fact they are quite advanced. Whereas learning how to read the hook switch IS a good Arduino beginner project.