Switch vs Linear Output

Switch sensors like the A3144 give a clean ON/OFF digital signal, perfect for counting, limit switches and door sensors. Linear sensors like the SS49E and AH49E output a voltage proportional to field strength, read with an ADC for position and proximity.

Unipolar, Latch or Omnipolar

A unipolar switch (A3144) turns on with one pole and off when it leaves. A latch (US1881, SS41F) turns on with one pole and stays on until the opposite pole arrives, which is what BLDC commutation and ring-magnet RPM sensing need. Omnipolar parts react to either pole.

Supply Voltage & Logic Level

Classic switches such as the A3144 are rated from about 4.5V upward, while 49E linear sensors run from roughly 3V. The AS5600 and MLX90393 boards are 3.3V parts. Match the supply and make sure the output never exceeds your MCU’s pin voltage.

Bare Part vs Module

Bare TO-92 sensors are cheap and tiny, ideal for custom PCBs and tight spaces, but you add the pull-up resistor yourself. Modules like the KY-003 and KY-024 add the resistor, an indicator LED and header pins for instant breadboard use.

Angle & 3-Axis Sensing

When you need absolute shaft angle or the full X, Y and Z field vector, step up to an integrated chip. The AS5600 reads a diametric magnet as a 12-bit angle, and the MLX90393 reports all three axes digitally over I2C or SPI.

If you are designing your own board, building a compact tachometer or need many sensors, skip the modules and buy the bare A3144. This EPLZON 20-pack lists a 4–24V supply and an extended −40 to 125°C range, which suits 12V automotive and industrial-style projects. The output is open-collector, and that is actually an advantage on 3.3V boards: power the sensor from 5V, add a 10kΩ pull-up from the output to 3.3V, and the signal is safe for an ESP32, Raspberry Pi or Pico GPIO. The small TO-92 body fits inside a motor housing, a bike frame or a 3D-printed bracket. Our A3144 pinout and working guide covers the details.

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The AS5600 packs an array of Hall elements and a signal processor into one chip that reads the angle of a diametrically magnetized magnet spinning above it. The result is a 12-bit absolute angle (4096 positions per revolution) over I2C, or as a PWM or analog voltage, with no contact and no wear. That makes it the favourite sensor for closed-loop stepper motors, gimbal and FOC brushless motor controllers, robot joints and smart knobs. WWZMDiB’s four-pack lists 3.3V operation, which matches ESP32, STM32 and Raspberry Pi Pico boards directly. One practical tip: on many cheap AS5600 boards the DIR pin is left floating, so tie it to GND or VCC or the reading may jump around.

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The KY-024 puts a 49E-class linear Hall sensor on a board with a comparator and a trim potentiometer. You get the best of both worlds: the analog pin gives you the raw field reading for an ADC, and the digital pin switches when the field crosses a threshold you set with the pot, so it works as an adjustable-sensitivity magnet switch too. That is handy for speed counting where the magnet passes at different distances, or for tuning a trigger point without touching code. The standard KY-024 layout exposes AO, GND, VCC and DO pins; check the photos on the listing to confirm the pinout before wiring.

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Not sure which Hall behaviour your project needs? This kit gives you ten each of eight common parts, covering every major family: unipolar switches (A3144E, OH137, ATS177), bipolar sensors and latches (SS40AF, SS41F and the popular US1881 latch used for BLDC motors and ring-magnet RPM sensing) and linear sensors (SS49E and the older AH3503). It is the cheapest way to try each type on a breadboard, and it doubles as a stock of replacement sensors for repairing fans, brushless motors, e-bikes and printers. Look up each part’s datasheet, because supply ranges and pinouts differ between families.

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The Melexis MLX90393 is a full 3-axis Hall magnetometer on a chip. It measures the X, Y and Z components of the field and returns them as digital values over I2C or SPI, with programmable gain and resolution so you can trade range for precision. That opens up projects a single-axis sensor can’t do: 3D joysticks, linear and rotary position tracking, magnet-based gesture input and tamper detection. This listing is a two-pack of the common purple breakout. Honest caveats: it is a no-name seller with no reviews yet and slow international shipping, so order early. Our MLX90393 with Arduino tutorial walks through wiring and code.

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Detecting a door, lid or limit position?

Start with the HiLetgo KY-003 module: magnet near, output LOW, no extra parts needed.

Measuring distance, position or field strength?

Use the 49E (SS49E / AH49E) linear sensor and read it with your ADC.

Counting RPM on a custom PCB or 12V system?

Buy the bare A3144 20-pack and add your own pull-up resistor.

Need motor shaft angle or a rotary encoder?

The AS5600 gives a 12-bit absolute angle from a single magnet.

Repairing BLDC motors or learning every type?

Get the VANXY 80-piece kit with US1881 latches, switches and linear parts.

Tracking a magnet in 3D?

Choose the MLX90393 for X, Y and Z field readings over I2C or SPI.

What is the difference between the A3144, SS49E and AH49E?

The A3144 is a digital unipolar Hall switch: its open-collector output pulls LOW when a south pole gets close enough and releases when it moves away, so it tells you only whether a magnet is present. The SS49E (originally Honeywell) and AH49E (Diodes Incorporated) are linear sensors: their output voltage sits near half the supply with no field and moves up or down in proportion to field strength and polarity. The SS49E and AH49E are pin-compatible and can usually replace each other, though exact sensitivity differs slightly between manufacturers.

Can I use a Hall effect sensor with an ESP32 or Raspberry Pi (3.3V)?

Yes, with a little care. A bare A3144 should be powered from 5V, but because its output is open-collector you can pull it up to 3.3V with a 10kΩ resistor and it is safe for 3.3V GPIO. Modules like the KY-003 pull the output up to their own VCC, so on 5V use a voltage divider before the GPIO pin. The 49E linear sensors run directly from 3.3V, and the AS5600 and MLX90393 boards are 3.3V parts. Note that the Raspberry Pi has no ADC, so a linear sensor needs an external ADC there. The ESP32 also had a built-in Hall sensor, but it is very insensitive and was dropped from newer ESP32 chips, so an external sensor is the better choice.

Why is my A3144 Hall sensor not detecting the magnet?

The three most common causes are the wrong pole, a missing pull-up and reversed pins. The A3144 only reacts to the south pole facing its branded (marked) face, so flip the magnet. A bare sensor needs a pull-up resistor (or INPUT_PULLUP) on the output, otherwise the pin floats. Finally, looking at the marked face with leads down, the pinout is VCC, GND, OUT from left to right; it is easy to insert backwards. Weak fridge magnets may also be too weak, so test with a small neodymium magnet.

Which Hall sensor should I use to measure motor or wheel RPM?

With one magnet glued to the shaft or wheel, a unipolar switch like the A3144 or KY-003 is all you need: count falling edges on an interrupt pin and divide by time. If you use a multi-pole ring magnet with alternating north and south poles, a latch such as the US1881 or SS41F (both in the VANXY kit) gives a clean square wave with one transition per pole. If you need speed and exact shaft angle, use an AS5600 instead.

Can a Hall effect sensor measure current?

Yes, that is how isolated current sensors such as the ACS712 work: an internal Hall element measures the magnetic field created by current in a conductor. You can experiment with a 49E sensor in the gap of a slotted ferrite toroid, but accuracy and calibration are hard to get right. For real current measurement, a dedicated Hall current sensor IC is far easier; see our best current and voltage sensors buying guide for proven options.