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A resistor limits how much current flows through a wire. It is the part that stops sensitive components from drawing too much and burning out. 🔥

Resistance is measured in ohms, shown by the symbol Greek omega. More ohms means more push-back, so less current gets through.

Ohm's Law ties it together: voltage equals current times resistance. Know any two values and you can find the third.

Rearrange to find current: I equals V divided by R. Bigger resistance gives smaller current for the same voltage.

An LED has almost no resistance of its own. Without a resistor it gulps too much current and dies in a flash.

Your pin gives 5V and an LED uses about 2V. The resistor must drop the leftover 3V, and that number sets its size.

A typical LED is happy near 10 to 20 milliamps. Aiming for about 15mA keeps it bright without stressing the pin.

Plug it in: 3V divided by 0.015A is 200 ohms. A common 220 ohm resistor is the easy, safe choice.

Resistors show their value with color bands. A 220 ohm part reads red, red, brown, a pattern worth memorizing.

Good news: a resistor is not polarized. You can plug it in either way and it works exactly the same.

Unsure of the exact value? A slightly larger resistor just dims the LED a touch. That is far safer than too small. 👍

Apply Ohm's Law to a real choice.

You can now size a resistor with Ohm's Law: divide the leftover voltage by your target current, then round up to a safe standard value. 🎉