This document is a schematic for a digital clock that uses an ATMEGA328P microcontroller and a DS3231 real-time clock module. It includes four 7-segment displays driven by HDSP-5501 LED driver chips, four buttons for input, a buzzer, and a 16MHz crystal oscillator. The microcontroller is connected to the real-time clock module via the SCL and SDA pins for timekeeping. Power is supplied to most components from the 5V rail.