If you ever work with a circuit that controls a decent amount of current, you will often encounter a FET – a Field-Effect Transistor. Whether you want to control a couple of powerful LEDs ...

He wound up using two common NPN transistors and 4 1K resistors ... it is actually pretty good. In all fairness, though, [Kevin] may have two transistors, but he’s only using one of them ...

The first transistor was about half an inch high. That's mammoth by today's standards, when 7 million transistors can fit on a single computer chip. It was nevertheless an amazing piece of technology.