ATmega328p clock with Li-ion battery management
Simple clock, based of 32768 Hz crystal oscillator with automatic brightness control and power saving modes for backup Li-ion 18650 type battery.
Display is TM1637 7-segment LED i2c module
Fine clock calibration can be achieved by changing weekly correction value: hold Snoose + Alarm + Hours/Minutes to decrease/increase value.
Original schematics and some pictures can be found here