● Covered by 1 source · 1 reportLow impact1 neutral
RotaryCell Project Enables Unmodified Rotary Phones to Function Over LTE with ESP32-S3
Key points
- RotaryCell converts rotary phones to LTE cellular without modification.
- Uses ESP32-S3, A7670 modem, and AG1171 for phone line interface.
- Prototype is functional; PCBs are awaiting assembly and validation.
- The system is battery-powered and portable.
Project Overview
The RotaryCell project has successfully created a system that allows an unmodified rotary telephone to function as a self-contained, battery-powered, portable cellular telephone. The design integrates new electronics reversibly inside the existing telephone casing, preserving the original handset, rotary dial, switch-hook, mechanical ringer, network block, and jacks.
Technical Implementation
The core of the system includes a LilyGO T-A7670G-S3 Standard board, which provides an ESP32-S3 controller, an A7670 cellular modem, battery charging capabilities, and a cellular audio interface. A Silvertel AG1171 subscriber-line interface operates the telephone line circuitry, detects the switch-hook, and drives the mechanical ringer. An additional Audio and Reset A4 PCB manages adjustable audio conditioning and a hardware power-cycle circuit for modem recovery.
Current Status and Components
A working hand-wired prototype has been developed and tested, running firmware version v0.10.4. Integrated PCBs for the Audio and Reset A4, and the AG1171 Carrier Through-Hole, were ordered on August 27 and 28, 2026, respectively, and are currently awaiting assembly and validation. The system is powered by a single protected 21700 cell connected to the LilyGO board.
Portability and Use Cases
The completed prototype is portable and can be operated away from a fixed telephone connection. This enables the use of the original desk telephone in various settings such as meetings, demonstrations, or any location with compatible cellular service, extending the utility of vintage hardware into modern communication environments.
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Primary sources
GitHub cmc_internal/api GitHub github/collect GitHub fregacmols/RotaryCell GitHub _private/browser GitHub get-started/accessibility GitHub open-source/sponsorsReporting from
The RotaryCell project developed a method to convert a traditional rotary telephone into a portable, battery-powered cellular phone using an ESP32-S3 and LTE modem without altering the original phone's components. This allows vintage telephones to operate on modern cellular networks, making them usable in new contexts.