Each of these modules contains three LEDs, arranged as a traffic light (red, yellow, green). The LEDs are provided with series resistors, allowing the module to be connected directly to an Arduino (5 V). Can also be used with micro:bit (3 V) with reduced light intensity. The anodes are brought out to individual pins while the cathodes are connected together in a common GND pin (0 V).
If you use D2-D13 and A0-A5 as digital outputs on an Arduino Uno, you can control up to six of these traffic lights – enough for rather complicated models of crossroads.
Can also be used with micro:bit (3 V) with reduced intensity. Note that each LED draws up to 5 mA. A micro:bit must not feed more than 3 LEDs simultaneously.