With a multiplexer. The two MUX input pins are connected to the two available on the arduino. supply the voltage to the MUX and connect the LEDs with resistors to gnd.
2 pins => 4 leds
With a multiplexer. The two MUX input pins are connected to the two available on the arduino. supply the voltage to the MUX and connect the LEDs with resistors to gnd.
2 pins => 4 leds