Modify an analog phone to replace main board.
The modification of an analog phone is fairly simple. The hook switch needs to be converted to a simple normally open switch. I do this with a relay. This works because you can buy a Single Pole Double Throw switch if needed or a
Quadruple Pole Double Throw (one coil operating 4 independent switches with the capability of two switch positions.) as will be the case in the phone that I am modifying. Ether way, you should buy a relay that is Double throw, this way it does not matter if the switch is Normally Open or Closed. Most older phones are actually like the one I will be using. It has a hook switch that is actually 3 switches. One of three is Normally Open, The other is Normally Closed and the last one has two potential positions. The only reason I am working with a relay that has another position is because I want to be able to signal the Arduino so it knows when you pick up the phone. Just like a real payphone it will switch from the "Hey! use me!" screen to the "Oh thank god you're using me, now my life is justified" screen.
NOTE: If you have the three switches be careful not to mix up the switches. a result if you do will be it will be VERY quiet, or not work at all.
Incase your interested the 4PDT relay I am using is a Potter & Brumfield Guelph, Ont. KHP17D11 24vDC Relay
I used the hook switch inside the payphone to operate the 24vDC power supply to trip the relay.
We will also need to modify the handset, keypad and line in plug.
Most of these modifications are VERY simple. Handsets on a Millenium phone are actually already an RJ11 mini (Same as a standard handset on 99% of all analog phones). So no real mod needed.
Line in plug I changed to use a surface mount phone line box so I would have the option of screw terminals in the future, you can even just twist the wires together if you must. So its all optional.
The keypad is the biggest pain in the ass, and even its not that bad. In this keypad