You can't see electricity. That's the whole problem.

The three numbers everything else is made of, the one equation that ties them together, and the schoolmaster who was called a fraud for finding it.

The part you reach for most, in the four arrangements that cover almost every circuit.

The first thing everybody wires up, and the first thing everybody destroys.

Two plates and a gap nothing crosses. It blocks a steady voltage, passes a changing one, and every board you own has a dozen of them holding the rail up.

3.3 V against 5 V, and how much current the whole board actually draws.

The part that only lets current through one way — charges about 0.7 V for the privilege, holds a fixed voltage when you push it backwards hard enough, and can be talked into storing a number.

A pin can drive 20 mA. Everything bigger needs a part in between — three legs, two flavours, and one number to get right.

The switch you turn with a voltage instead of a current. Four short pages, mostly moving pictures, ending with the one word on the datasheet that decides whether it works from a 3.3 V pin.

The part that will not let its current change. Four pages on a coil of wire, what it stores, the rating that is not about heat, and the circuit the whole site has been telling you to use instead of a linear regulator.