A3144 Hall Effect Sensor
Digital hall-effect switch for RPM counting and proximity.
A digital Hall-effect sensor used for contactless RPM counting, door-open detection, and brushless motor commutation sensing. The A3144 outputs a simple digital signal that switches state whenever a sufficiently strong magnetic field (from a passing magnet) is detected nearby, with no moving parts and no physical contact required — a common building block for spinning-wheel RPM sensors, door/window open detection (as a solid-state alternative to a reed switch), and sensing magnet positions on brushless DC motors.
Specifications
| Sensor type | A3144 digital Hall-effect switch (unipolar, latching-free — switches back off when the magnet moves away) |
| Operating voltage | 4.5V–24V DC (5V typical for microcontroller projects) |
| Operating current | ~9 mA typical |
| Output type | Open-collector digital output — requires an external pull-up resistor (often included on breakout boards) |
| Response | Output switches LOW when a sufficiently strong magnetic pole is detected, HIGH otherwise (with pull-up) |
| Detection distance | A few millimeters, dependent on magnet strength and orientation |
| Response speed | Fast enough for RPM sensing on typical hobby motors and wheels (well into the kHz range) |
| Interface | Single digital output pin, read directly or via interrupt for pulse counting |
Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 4.5–24V DC (5V typical) |
| 2 | GND | Ground |
| 3 | OUT | Open-collector digital output — connect through a pull-up resistor (or use the microcontroller's internal pull-up) to a digital input pin |
The bare A3144 IC has an open-collector output and needs an external pull-up resistor (typically 10kΩ to VCC) to read a clean HIGH when no magnet is present — most breakout boards already include this pull-up onboard, so check your specific board before assuming one is needed. Because the output is unipolar and switches state only for one magnetic pole, the orientation of the passing magnet matters: test which face needs to point at the sensor before finalizing a mechanical design.
Variants
The A3144 is the right choice for simple on/off magnetic detection like RPM counting or door-open sensing where power is already available. If you'd rather avoid any powered electronics entirely for a simple door sensor, a passive reed switch is a valid zero-power alternative; if you need to know how close the magnet is rather than just whether it's present, a linear Hall sensor with analog output is more appropriate.
| Variant | Price |
|---|---|
| A3144 breakout | ~$0.50-1.50 |
| Reed switch | ~$0.20-1 |
| US5881 / SS49E (linear Hall sensor) | ~$1-3 |