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RotaryCell: Making an unmodified rotary phone work over LTE with an ESP32-S3

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Why This Matters

RotaryCell innovatively transforms classic rotary phones into portable LTE-enabled devices without altering their original hardware, bridging vintage design with modern connectivity. This development offers a nostalgic yet practical solution for users seeking wireless communication while preserving historical equipment, impacting both tech enthusiasts and the telecommunications industry. Its open-source approach encourages DIY customization and innovation in retro tech integration.

Key Takeaways

RotaryCell

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.

Reproduce the working prototype by hand

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.

Current baseline

This repository records the project as it stood on August 28, 2026:

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