This project is developed by Ivo Zivkov (who is also the programmer of the "Casio G-Shock Smart Sync" app).
This little device is ideal for people who just want their bluetooth watches to be accurate, but don't want to run a smartphone in order to sync time. It's also for people, who don't want an overloaded app like the Casio Watches app, which has so much more than just time syncing.
What do you need?
Hardware:
You need an ESP32 mikro controller. These little devices are available without screen or with a little 1,47" touch screen.
In 2025 the prices for the devices on Amazon were around 11€ (no screen) or 23€ (with screen).
Check the projects GitHub page for the exact hardware requirements.
Software:
The required software can be downloaded from the projects GitHub page.
The project page also describes how to put the software onto the device and how to configure it.
The device connects to the internet to get the time for your specified time zone. Then it listens if any bluetooth watch wants to connect and provides them with the correct time.
Does it work with all bluetooth G-Shocks?
It works with a lot of G-Shocks, even some regular Casios, ProTreks and Edifice models.
Ivo and I tested it on all models we had. There is a list of models which work flawlessly and also a list of watches we could not get to connect to the ESP32 on the GitHub project page.
Basically, all newer bluetooth models work just fine.
How to connect my watch?
Manual time sync:
Just press the connect button (depending on the watch model) in order to perform a manual time sync.
Automatic time sync:
The watch will sync automatically, when the "auto time adjustment" option is turned on (check manual of your specific watch).
How do I know if a watch has been synced?
The display of the device will show the last watch, that has been synced.
There also exists a little android app. This app can be used to configure your ESP32 device and also has a log of the last 10 activies.