prerequisite: Electricity

electrical circuit - controlled by mechanical switches

electronic circuit - controlled by electronic signals

electronics begins with the vacuum tube and the transistor

Can be used in these ways:

• current limiting
• voltage limiting
• pull-down
• pull-up

Wire in series with an LED.

Create a voltage divider circuit with two resistors.

Limit voltage to any value.

Place between an open switch and ground, to force the switch to appear open.

Place resistor between an open switch and the voltage source, to force the switch to appear closed.