When I started looking into what would it take to make to old simple phones (the ones that get their power from the phone line), I realized pretty quick that this was the easy part.
Each phone (and phone base) has a phone cord running out of it, which has two wires — red and green. To establish a connection between two phones, all we need to do it connect the green wires directly, and connect the red ones through a 9V battery, and a resistor, as shown here.
However, the tricky part is to make the phone ring on one side, when the phone on the other side is picked up. The very detailed solution in this video suggests a circuit that enables that.
For now, I created a simple prototype which is identical to the system shown in the video above.
However, the shorter version of the video above also discusses the voltage needed. what I understand is that if I need the phones to be connected with a longer cable (1–2 km), which sounds about right for my project, I will need something stronger than 9V battery.
For now, I found this in an Opshop, but I haven’t checked how long it is:
So the next thing I need to figure out is how much power I will need exactly, and also, where will I get it from.
Ultimately, I would like to use a battery that can be charged using a solar panel whilst feeding the system. I haven’t done much research about it yet so that is my next step, and also, I will probably need two of those, which has the potential of being expensive.
