For the most basic design, you need: a battery powering a circuit a spring-driven metal switch built into a door frame a magnet embedded in the door, lined up with the switch a separately-powered buzzer with a relay-driven switch. When the door is closed, the magnet pulls the metal ...
If you’ve ever driven a rental car at night and realized the headlights were set to “off,” you start to appreciate the automatic headlights you might have in your own car. Seeing and being seen in a vehicle have been paramount since the invention of the car itself, but headlights have...
a separately-powered buzzer with arelay-driven switch. When the door is closed, the magnet pulls the metal switch closed so the circuit is complete. The current powers therelay's electromagnet, so the buzzer circuit stays open. When you move the magnet by opening the door, the spring snaps...