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Pegor's F91 Kepler Is a Work-in-Progress Open-Hardware Smartwatch Reboot of Casio's Classic F-91W

After experiencing burnout on the project, maker "Pegor" is seeking assistance with bringing the F91 Kepler over the finish line.

Gareth Halfacree
2 years agoWearables / HW101 / Retro Tech

Pseudonymous maker "Pegor" has released a work-in-progress "reboot' of Casio's F-91W digital watch as a modern smartwatch, dubbed the F91 Kepler, under a permissive license — in the hopes of attracting additional developers to the project

"The F91 Kepler is complete redesign of the classic Casio F-91W watch," Pegor explains of the open hardware effort. "This project completely replaces the original internals of the watch only keeping the original case and adding an OLED display and a Bluetooth-capable MCU [Microcontroller Unit]."

Originally released in 1989 as the follow-up to the Casio F-87W, the F-91W — designer Ryusuke Moriai's first for the company — is a chronograph watch with net and lap time modes, an hourly chime, daily alarm, and an annual calendar. Compared to a modern smartwatch, though, the feature set is a little spartan — the calendar doesn't even understand leap years, never mind offer CalDav synchronization — leaving the iconic watch ripe for an upgrade.

Pegor's replacement hardware, built around a Texas Instruments CC2640 Arm Cortex-M3 chip with Bluetooth Low Energy (BLE) capability, sits inside an original F-91W housing and offers smartphone connectivity with call and message notifications appearing on a bar to the top of the OLED display. At the time of writing, though, a number of features were missing: Only a single one of the watch's buttons works, as a screen-wake button designed to boost battery life to 15 days per charge, and there's no companion app for the phone side.

"At this point," Pegor explains of the project's status, "(read more like year ago,) I am burnt out from this project and now I figured to open it up and hopefully more people can be involved." As a result, the maker has published the hardware design files, firmware, and "completely unfinished software" under a permissive license.

Pegor isn't the only maker who misses the Casio F-91W form factor but wishes for modern innards: Joey Castillo, of Oddly Specific Objects fame, designed his own replacement motherboard dubbed the Sensor Watch — but while the Sensor Watch retains the original Casio LCD, the F91 Kepler comes with its own graphical OLED panel — reusing only the case from the original watch.

All the files for the F91 Kepler are available in Pegor's GitLab repository, under the permissive MIT license.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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