In this project you can bulid an real time clock using arduino mega and basic programming skills

First you need an arduino mega and a rtc ds1307 module, connect it to the board using i2c comunication, it means that you need to know where are the sda and scl pins, feed the module with a coin 3v battery and 5v from the board, for module configuration you need an rtc library, search it through the web, try connecting leds to the board to show the binary time or you can show it using the serial port.