Addressable RGB LEDs are practical components that can be stringed together easily. Here, we shaped the string as a 7-segment digit and put it on a stylish black PCB.

Four LEDs per segment plus a decimal point and a colon. This means 31 LEDs per digit.

Solder jumpers are provided for shorting optional LEDs. The DIN and DOUT pins of unmounted LEDs must be shorted; otherwise the data signal can’t pass through.

The PCB pooling service chosen to produce the board (if you use one) can destroy the stylish look as they tend to put a production number somewhere on the board in a random spot, the most probable place being there where you really didn’t want it. Luckily, some pooling services let you specify a position for this number, so choose carefully. The result is a stylish black board with diffused-light-type LEDs on it.

An Arduino sketch to control the three digits as one display is available below. The Adafruit_NeoPixel library drives the LEDs. As my LEDs are rather old, the data rate must be set to 400 kHz. Modern versions of these LEDs usually run at 800 kHz.

All the design files are available below.