Make: More Electronics

Chapter 30. Experiment 30: Hidden Detectors

Hall-effect sensors are all around you. When you close the lid of your laptop, probably a Hall sensor under the plastic skin of the case detects the action and puts the computer into sleep mode. When you switch on your pocket camera, a Hall sensor detects that the lens is fully extended. Hall sensors are inside your hard drive, detecting the rotation of its motor and controlling its speed. They’re in the electronic ignition of your car—and in the car’s door lock, which switches on the interior light when your key turns. Your modern washing machine may use a Hall sensor to determine if the door is closed. Similarly, your microwave oven.

Each sensor generates a tiny electric current in response to a magnetic ...