It all starts with the HC-05 Bluetooth module, which is meant to transfer serial data, but which can be converted into a general-purpose device costing ten times as much with a simple Flash ROM ...

On the other side, a ATMEGA328P microcontroller along with another HC-05 drives two 8×8 LED matrices with MAX7219 controllers. Everything is powered by a 18650 lithium-ion battery with a 134N3P ...

This works well if your board connects to your computer via a USB cable and a USB-to-serial chip, but some applications might require a wireless option. Fortunately, Bluetooth modules like the HC-05 ...