Rotary Phone Converted to DECT Wireless Standard

from hackster.io

DECT (Digital Enhanced Cordless Telecommunications) is a wireless telephone standard that was widely adopted in Europe and many other areas, but was largely bypassed in North America per US radio-frequency regulations.

Andreas Klausen decided to hack a vintage rotary Lyon Phone, used by the German Federal Post Office circa 1980, to take advantage of the DECT wireless standard.

A NodeMCU ESP32 module is implemented as the brains of this new phone setup, and instead of trying to integrate phone functions natively, the ESP interfaces with a donor DECT handset by switching the buttons via IO pins.

To receive calls, a phototransistor attached to the phone’s handset blinker detects this incoming condition, and is thus able to signal the phone’s original bell to ring. It can also tell when the phone’s handset is placed on the receiver switch for activation/deactivation. Since the older phone’s microphone didn't work with the DECT device, this newer unit was simply extracted and placed into the old (now-enhanced) headset.

While you may or may not have access to a DECT and/or rotary phone, it’s an interesting example of what you might call “brute force” hardware hacking–simulating a human input rather than trying to re-engineer the black box that is the DECT device. Code for the build can be found on GitHub for your perusal and/or reuse.