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RotaryCell: Making an unmodified rotary phone work over LTE with an ESP32-S3
RotaryCell converts a traditional rotary telephone into a self-contained, battery-powered, portable cellular telephone without modifying the original telephone.
The design continues to use the original handset, rotary dial, switch-hook, mechanical ringer, network block, and existing jacks. The added electronics mount reversibly inside the case; no original telephone parts need to be drilled, cut, or permanently altered.
The working prototype can be carried and operated away from a fixed telephone connection, making the original desk telephone usable at meetings, demonstrations, or anywhere compatible cellular service is available.
This is a working engineering archive rather than a finished construction release. The hand-wired prototype operates, while the first integrated PCBs are currently awaiting assembly and validation.
The complete point-to-point wiring and component reference is the primary starting point for recreating the proven hand-wired prototype:
Open or download the full-resolution printable PDF. It covers the LilyGO, protected 21700, passive audio components, AG1171, GPIO connections, and original Model 500 circuitry without using the new PCBs. A hand-wired installation fits inside the telephone, but arranging and insulating all of the loose components and wiring is challenging; expect repeated dry-fitting and careful routing.
This repository records the project as it stood on August 28, 2026:
See STATUS.md for the distinction between tested prototype behavior and hardware awaiting validation.
The telephone's RJ11 line jack is used only to deliver regulated 5 V to the LilyGO charging input on the designated pins. It does not power the AG1171 directly and is not used as a telephone-line interface.
For a hand-wired build, start with the complete prototype wiring reference. For the newer PCB implementation, continue with STATUS.md, current hardware wiring, the master BOM, the assembly guide, and BUILDING.md.