If one wants to display 3 digits, three displays should be used. There are many circuits available for 2-digit up/down counter but using a microcontroller reduces components and space on the board but ...

This is a simple 0 to 9 counter circuit constructed using Arduino! Here, a common cathode 7-segment LED display is connected to Arduino for displaying the digits. The code (Arduino sketch) allows push ...

Speaking of hardware, the clock is a pretty standard mashup of an Arduino Pro Mini clone and a DS3231 I2C clock. The Neopixel strips are 60-per-meter WS2812B LEDs with two LEDs per digit segment.