Okay, NoObisch Q, I wonder how I would know how many Ohm a resistor should be, when I am designing a circuit on my own. Like the KnightRider example, they use 220 Ohm, why (and why use a resistor here anyway??) I am also using Google offcours, but here I have a feeling I can ask stuff I don't get…

How do I know what resistor to use??

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