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Learn the basics

Resistor

The small part with coloured bands that keeps the current small: why an LED needs one, and how to read 220 Ω from the colours.

A resistor with the colour bands red, red, brown and gold

Resistor

A resistor makes it harder for current to flow. With an LED it keeps the current small, so the LED and the board's pin stay safe. It works either way round.

For an LED: 220 Ω, the bands red, red, brown (and a gold one).

More: reading the colours

Hold the resistor with the gold band on the right. The first two bands are digits, the third says how many zeros follow:

black 0brown 1 red 2orange 3 yellow 4
green 5blue 6 violet 7grey 8 white 9

red red brown = 2, 2 and one zero = 220 Ω (ohm). More ohms let less current through, so the LED gets dimmer. On the Micro:bit (3 V) LEDs are a bit dimmer than on the Arduino (5 V); a blue LED needs almost 3 V and looks dim on the Micro:bit.