How Does a Hall Effect Sensor Work?

A Hall effect sensor lets your project sense magnets and measure rotation, and Compoden's AI build assistant helps you wire one into a speedometer, a contactless switch, or a position detector. These sensors are everywhere, from bike computers to motor controllers. This article explains the physics behind them, the signals they produce, and how to read them on an Arduino or ESP32.

The working principle

The Hall effect is a real piece of physics named after the scientist who discovered it. When current flows through a thin slab of conductive material and a magnet is brought near, the magnetic field pushes the moving charges to one side of the slab. This sideways push builds up a small voltage across the slab, at right angles to the current. That voltage is called the Hall voltage, and it grows or shrinks with the strength and direction of the magnetic field. A Hall effect sensor contains such a slab plus an amplifier, so a faint Hall voltage becomes a usable signal. Crucially, it senses the magnet without any contact, which means no wear and a long life.

How it outputs a signal

There are two common types. A digital Hall sensor, often a switch type, gives a clean HIGH or LOW: it flips when a magnet of the right polarity comes close enough and flips back when the magnet leaves. This is ideal for counting and detection. A linear, or analog, Hall sensor instead gives a voltage that varies smoothly with field strength, so it can measure how strong or how near a magnet is, and even tell which pole is facing it. Many hobby modules use the switch type with a clean digital output pin.

How you read it on a microcontroller

For a digital Hall sensor, wire VCC and GND to power and ground, then connect the output to a digital input on your Arduino or ESP32 and read HIGH or LOW. To measure rotation speed, fix a magnet to a spinning wheel and place the sensor nearby; each pass of the magnet produces a pulse, and counting pulses over time gives revolutions per minute. Using an interrupt pin lets you catch fast pulses reliably. For a linear Hall sensor, connect the output to an analog input and read the changing value to gauge field strength or position. Keep in mind the magnet's polarity, since switch-type sensors usually respond to one pole.

Common uses

Hall sensors are used in bike and motor speedometers, brushless motor control, contactless limit switches, lid and door position sensing, current sensing, and tamper-proof buttons. Because they work without contact, they are reliable and durable. Their main considerations are getting the magnet polarity and spacing right and choosing between the digital switch and the linear type for your task.

Build it with Compoden's AI

Deciding between a switch-type and a linear Hall sensor, and setting up pulse counting, is straightforward with help. Compoden's AI build assistant recommends the right Hall sensor, explains magnet polarity and placement, and shows how to read pulses or analog values on your Arduino or ESP32, including using interrupts for speed measurement. Tell it whether you are building a speedometer, a contactless switch, or a position sensor, and it suggests parts and code. Browse our collection and keep the assistant close.

Sense magnets in your next build. Browse Hall effect sensors at Compoden and let the AI build assistant guide you.

What does a Hall effect sensor detect? It detects magnetic fields. A magnet near the sensor's conductive slab pushes the flowing charges sideways, creating a Hall voltage that the sensor amplifies, so it can sense a magnet's presence, strength, or polarity without any contact.

Is a Hall sensor digital or analog? Both types exist. A switch-type Hall sensor gives a digital HIGH or LOW when a magnet is near, ideal for counting and detection, while a linear Hall sensor gives a voltage that varies with field strength for measuring position or magnitude.

How do I measure speed with a Hall sensor? Attach a magnet to a rotating part and place the sensor beside it. Each pass produces a pulse, so count the pulses over a known time to calculate revolutions per minute. Using an interrupt pin helps catch fast pulses reliably.