LESSON 10 · Components
LEDs
A diode that gives off light — and the first component most beginners light up.
A Light Emitting Diode is a diode that emits light when current passes through it in the allowed direction. Like any diode, it has polarity: the longer leg is the anode (positive), the shorter leg the cathode (negative).
LED SYMBOLA diode symbol with two small arrows, showing light being emitted.
LEDs need a resistor in series to limit current — connect one directly to a battery and it will usually burn out instantly.
QUICK RESISTOR MATH
R = (Vsupply − Vled) ÷ Iled — for a 9V supply, a red LED (≈2V drop) and a target 15mA, that's (9−2)÷0.015 ≈ 467Ω, so round up to 470Ω or 1kΩ to be safe.