Hardware

• Microcontroller: Atmega328p with Arduino bootloader
• Real Time Clock: Maxim DS3231 (<2min per year deviation)
• Display: 96×96 pixel Sharp Memory LCD (LS013B4DN04)
• Battery: CR2025 160mAh coin cell

Features

• The ATmega is in Sleep mode for most of the time and only runs once a minute to update the time or if a button is pressed. This reduces the current consumption to 2uA. Sady the display needs a certain pulse every second, which requires a complicated additional circuit. Because of this the current consumption is around 20uA. This still makes for around half a year of battery life.
• User Interface controllable with three side buttons. Buttons are 3D-printed and activate switches on the PCB
• Tells time, date, temperature and battery voltage on the main screen. No additional temperature sensor is needed, because the DS3231 already has one integrated for temperature compensation.
• Stopwatch
• Flappy Bird clone (“That would have been cool in 2013”)
• The case consists of four 3D-printed parts. It has a thickness of only 10.8mm, which is thinner than the Apple Watch. Unfortunately it lacks screen protection.
• Fits any 22mm Watchband

For more detail: Chronio – Low power Arduino based (smart)watch