RotaryCell has developed a method to convert traditional rotary telephones into self-contained, battery-powered cellular devices without modifying the original equipment. The design retains the original handset, rotary dial, switch-hook, mechanical ringer, network block, and existing jacks. The added electronics are mounted reversibly inside the case, ensuring that no original telephone parts are drilled, cut, or permanently altered.
The working prototype can be operated away from a fixed telephone connection, allowing the original desk telephone to be used in various settings such as meetings and demonstrations, wherever compatible cellular service is available. This project is documented as an engineering archive rather than a finished product release. The hand-wired prototype is operational, while the first integrated printed circuit boards (PCBs) are pending assembly and validation.
The project includes a complete point-to-point wiring and component reference, which serves as a starting point for recreating the proven hand-wired prototype. A full-resolution printable PDF is available for download, detailing the components used, including the LilyGO, protected 21700 battery, passive audio components, AG1171, GPIO connections, and the original Model 500 circuitry without the new PCBs. The hand-wired installation fits inside the telephone, but users should anticipate challenges in arranging and insulating the loose components and wiring, necessitating repeated dry-fitting and careful routing.
As of August 28, 2026, the repository documents the project's status, distinguishing between tested prototype behavior and hardware awaiting validation. The telephone's RJ11 line jack is utilized solely to deliver regulated 5 V to the LilyGO charging input and does not serve as a telephone-line interface.
For those interested in a hand-wired build, the complete prototype wiring reference is available. For the newer PCB implementation, additional resources such as STATUS.md, current hardware wiring, the master bill of materials (BOM), assembly guide, and BUILDING.md are provided. Dial service code 0000 initiates maintenance Wi-Fi, while service code 9999 performs modem diagnostics and software recovery, although it did not resolve the modem lockup issue noted in STATUS.md.
This public engineering and development archive aims to preserve a reproducible baseline, provide access to the working hand-wired prototype for other builders, and document progress toward a more integrated implementation. It is important to note that this repository is not a finished construction kit or production release. Files related to hardware and audio components record the exact board candidates ordered in August 2026, with their assembled operation yet to be validated. The repository tracks tested behavior, known failures, and documentation gaps in STATUS.md. Code and original documentation are licensed under the MIT License, while third-party datasheets, vendor names, trademarks, and historical telephone designs remain the property of their respective owners.