The Arduino pro micro is actually the small version of the Arduino Leonardo, based on the ATmega32u4. Due to its size, the board contains 12 digital input / output pins (5 of which can be used as PWM outputs), 4 (10 bit) ADC inputs, a 16 MHz crystal and a micro USB connection. Connect the sign to the computer and you can start immediately.
These boards, like the Leonardo, differ from previous boards, because the ATmega32u4 contains built-in USB communication, so that only a single microprocessor is needed on the board. This allows the board to be connected directly and used as a mouse or keyboard, because the USB communication goes through the same chip, the Arduino will log on and log off as a USB system when it is programmed or reset.
This Arduino is a clone, which means that this sign was not built in the original factory. The only difference between original and clones is that these Arduinos are cheaper. All components and circuits are otherwise identical.