OpenWear C3 Is a Smartwatch Platform Built From Bare PCB Up

Most DIY smartwatch projects start from a development board and work backward. Hansel Kay’s OpenWear C3 starts from a blank PCB layout and builds the whole platform up from there.

What They Built

OpenWear C3 is an open smartwatch platform centered on an ESP32-C3, with a custom PCB handling power regulation, sensor wiring, and display control rather than relying on an off-the-shelf dev board crammed into a case. Running on a 600mAh battery, it lasts roughly two to four days per charge depending on how features like raise-to-wake are configured.

How They Did It

The board was laid out in EasyEDA and fabbed through standard PCB houses like JLCPCB or PCBWay, with a voltage converter stepping input power down to a clean 3.3V rail for the microcontroller and sensors, plus the supporting passives for I2C pull-ups, battery voltage sensing, and backlight control. The design supports a MAX30100 heart-rate sensor, with the option to swap in a MAX30102 at the cost of some register-level firmware changes. On the software side, a good chunk of effort went into display handling specifically — tuning the wake and UI transition routines to cut down on the flickering and ghosting that’s a common annoyance on small embedded displays.

Go See It

Hansel Kay (hanselkay8) documented the full PCB design and firmware on Hackster.io under the project name “OpenWear C3,” including schematic and firmware details for anyone looking to build their own.