Rotary Cell 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. Reproduce the working prototype by hand using the complete point-to-point wiring and component reference, available as a full-resolution printable PDF covering the Lily GO, protected 21700, passive audio components, AG1171, GPIO connections, and original Model 500 circuitry.

The repository records the project as it stood on August 28, 2026: Firmware v0.10.4 is the current prototype-tested software. A Silvertel AG1171 subscriber-line interface operates the telephone line circuitry, senses the switch-hook, and drives the mechanical ringer. A Lily GO T-A7670 G-S3 Standard board supplies the ESP32-S3 controller, A7670 cellular modem, battery charging, and cellular audio interface.

Current functions include rotary pulse dialing, switch-hook detection, incoming and outgoing cellular calls, physical bell ringing, North American dial and reorder tones, bidirectional handset audio with adjustable levels, battery monitoring, and USB diagnostics.