After spotting some interesting military phones at a museum, [CuriousMarc] wondered what it would take to retrofit these heavy duty pieces of telecom equipment for civilian use. He knew most of the internals would be a lost cause, but reasoned that if he could reverse engineer key elements such as the handset and keypad, he might be able to connect them to the electronics of a standard telephone. Luckily for us, he was kind enough to document the process.
There were a number of interesting problems that needed to be solved, but the first and perhaps largest of them was the unusual wiring of the keypad. It wasn’t connected in the way modern hackers like us might expect, and [CuriousMarc] had to end up doing some pretty significant rewiring. By cutting the existing traces on the PCB with a Dremel and drilling new holes to run his wires around the back, he was able to convert it over to a wiring scheme that contemporary touch tone phones could use.
An adapter needed to be fabricated to mount a basic electret microphone in place of the original dynamic one, but the original speaker was usable. He wanted to adapt the magnetic sensor that detected when the handset was off the hook, but in the end it was much easier to just drill a small hole and use a standard push button.
The main board of the phone is a perfect example of the gorgeous spare-no-expense construction you’d expect from a military communications device, but unfortunately it had to go in the bin. In its place is the guts of a lowly RCA phone that was purchased for the princely sum of $9.99. [CuriousMarc] won’t be able to contact NORAD anymore, but at least he’ll be able to order a pizza. The red buttons on the keypad, originally used to set the priority level of the call on the military’s AUTOVON telephone network, have now been wired to more mundane features of the phone such as redial.
While this is fine for a one-off project, we’d love to see a drop-in POTS or VoIP conversion for these phones that didn’t involve so much modification and rewiring. Now that we have some documentation for things like the keypad and hook sensor, it shouldn’t be hard to take their idiosyncrasies into account with a custom PCB. Dragging vintage gear into the modern era is always a favorite pastime for hackers, so maybe somebody out there will be inspired to take on the challenge.