RotaryCell: An Unmodified Rotary Phone That Works Over LTE
RotaryCell: Making an unmodified rotary phone work over LTE with an ESP32-S3
RotaryCell is an open-source project that turns a classic rotary telephone into a portable cellular phone without any permanent modification. The system uses an ESP32-S3, an A7670 modem, and a Silvertel AG1171 subscriber-line interface to handle dialing, ringing, and audio, all powered by a single 21700 battery. The hand-wired prototype is fully functional, and the project provides detailed wiring diagrams, firmware, and PCB files for replication. It's a clever blend of vintage hardware and modern tech, offering a fully reversible way to bring a rotary phone into the cellular age.
The design continues to use the original handset, rotary dial, switch-hook, mechanical ringer, network block, and existing jacks.
- ralferoo
Accepting 5V over the RJ-11 jack seems asking for trouble. Someone is going to plug it into a regular phone socket at some point, so it needs to be capable of surviving at least 60VAC. Even if a secondary pair is used, there are so many different wiring standards in use, it'll end up plugged into something live sooner or later.
- walrus01
For the 21700 cell if you want to do this without spending a lot on batteries, but also be sure that any misconfigured hardware can't drain the battery below a damage threshold, use a button top protected 21700 cell. Here's a good 'house brand' one that is popular with 21700 flashlights.
https://liionwholesale.com/collections/batteries/products/pr...
- shrx
We have a similarly converted rotary phone at my local astronomy club's observatory, used to receive visitors. It's driven by an arduino if I remember correctly. The main issue is that the sound quality of its built-in speaker is quite poor, especially compared to modern cell phone speakers we're used to nowadays, with a narrow frequency window and frequent echoes.
- hi_hi
When I finally agree to cave in and buy a phone for my soon-to-be teenager, little does she know this is the phone I have in mind…
- ge96
That would be funny you're at a club with this phone and doing phone calls