Every time you brake your car, a tiny chip counts the wheel's rotation. Every brushless motor, every e-bike throttle — they all rely on the same trick: a Hall sensor, a chip that detects magnetic fields and turns them into electrical signals.
The trick in one paragraph
Run a small electric current through the chip and put it near a magnet. The magnetic field pushes the moving charges inside the chip to one side, so a small voltage appears across the chip. The stronger the field, the bigger the voltage. That's the Hall effect, discovered in 1879 — and today it's built into chips smaller than a fingernail.
Two kinds of Hall sensors
Hall switches act like a light switch: a magnet passing nearby turns the output on or off. That clean on/off signal is perfect for counting rotations and detecting position. Linear Hall sensors output a voltage proportional to the field strength, so they measure exactly how far a magnet has moved — like the throttle on an e-bike, where twisting the grip moves a magnet past the chip.
Where you'll find them
- Speed and rotation — ABS wheel sensors, engine speed, fans.
- Position — motor rotor position, joysticks, throttle grips.
- Current sensing — measuring the field around a wire instead of cutting it.
- Lid and door sensors — in laptops, phones and appliances.
Magnets and sensors, together
Hall sensors don't work alone — they need a magnet nearby, usually a small ferrite or bonded NdFeB piece. Glue a magnet to a spinning wheel and the sensor counts every pass; attach one to a moving part and the sensor tracks its position. No contact, no wear, no dust problems — just a tiny chip and a magnet doing the work.
Read on: the magnets used in sensors → · magnets in motors →