Here is a simple, yet useful circuit of an Arduino 4-digit 7-segment LED display unit. The module used here is a self-contained, compact common-cathode module containing four 7-segment LED numeric ...

Reddit user Krukerfluk has created an awesome DIY digital clock using 144 x seven segment displays, combining them to create a larger LED display powered by an Arduino Nano.

Inside the boxy blue base is an Arduino Nano, a DS3231 real-time clock module, and a perfboard full of transistors for switching the LED strips inside the segments.