# Starter Kit Project number 2 spatialship board

I would like to have an explanation about the use of resistance in the project number 2
spatialship board in the starter kit.

My question is? why the resistance of 220 ohms is used to connect leds to GND instead of connecting resistance to 5V?

I believed that resistance is used to absorb volts that entering into a led instead from 5v , instead to absorb the volts that go out from the leds towards GND?

The LED can be connected in both ways. If an output is HIGH it sources 5V to GND, and if it's LOW it sinks 5V from 5V. Only that difference is important to the LED, either 0 or 5V. If it's 5V, the LED shines and the current limiting resistor prevents it from smoking, consuming about 3V left over from the 2V LED.

What i understood in the project Starter Kit Project number 2 spatialship board , it is that the interruptor is into input mode through pin number 2 and sends volts to leds over the legg connected to pin number 2, so leds receive volts from interruptor over the cathod (the short leg of the cathod connected to mass), it is why resistor is connected to mass insted of being connected to 5v of the arrduino board

The input (pin 2) is unrelated to the LEDs. Each LED is connected to an output pin, which provides 0V or 5V, and to GND (0V).