In the project that converts an old rotary phone into a mobile phone, a subscriber line interface that emulates a copper telephone line is connected to a Lilygo ESP32-S3 board. The board manages the phone’s audio and control functions while communicating with the cellular modem, so no physical modifications are made to the device. The software simulates a North American telephone line with a dial tone and a ringing sound for incoming calls. Special codes for maintenance and diagnostics are also included.
Why it matters
The project’s distinguishing feature is that it can work with modern cellular communications while preserving the old phone’s original casing and method of use. By bridging the analog behavior of a telephone through the subscriber line interface with ESP32-based control, the solution becomes more than just a visual refresh—it reuses the old audio and control system. This approach is of interest to those who want to preserve rotary phones in a functional form, as well as those working on embedded systems. The maintenance and diagnostic codes ensure that the converted device can continue to be monitored and managed after it is put into use. However, the software’s reliance on North American telephone line behavior leaves open the question of how the same experience could be adapted to different telephone standards or regions.