Chapter 6. Movement
Automatic garden lights detect the moving heat radiated by humans. Joysticks convert motion to a change in resistance. A volume knob is a potentiometer, another kind of variable resistor.
Experiment: Which Way Is Up? (Tilt Ball Switch)
If you decide to build a pinball machine, you might want to detect excessive nudging and end the player’s turn with a TILT alarm. Also, a burglar alarm could use a tilt sensor.