Hall-Effect Sensor
Sensor
A chip that senses magnetic fields via the Hall effect. Digital versions switch like a contactless reed switch; linear versions output voltage proportional to field — hiding inside BLDC motors, current sensors and every phone compass.
What it looks like
Hall-Effect Sensor
A typical sensor — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Operate/release point
mTField to switch on and off (digital types).
Sensitivity
mV/mTLinear types: output slope around Vcc/2.
Supply voltage
VClassic parts 4.5–24 V; modern ones 3.3 V-friendly.
Output type
Open-collector (needs pull-up) on most digital parts.
Markings
TO-92 flat package printed with the part code (44E/A3144, 49E); the branded face is the sensing face.
Standard values
A3144/44E (digital switch), SS49E (linear), ACS712-05/20/30 (current modules).
How to choose
Unipolar switch for proximity, latching for motor position, linear for measuring field or current. Check magnet orientation — Hall sensors read one axis, through the package face.
Pinout & package
TO-92 — flat (branded) face toward you, legs down
Check first: Shown for the A3144/A3141 switch family. The output is open-collector, so it needs a pull-up. Ratiometric analogue types (A1302) and 4-pin latches differ.
TO-92: Vcc, GND, OUT (facing the printed side, left to right on most). Open-collector output needs a 10 kΩ pull-up.
Example circuits
- Contactless RPM counter with a magnet on a shaft
- ACS712 measuring motor current into an ADC
- Brushless motor rotor-position sensing
Common failures
Reverse supply kills them instantly; 'not working' is usually a missing pull-up or a magnet presented on the wrong axis/pole.
How to test
Power via 10 kΩ pull-up on OUT; bring a magnet's pole to the printed face — OUT snaps low (digital) or swings around Vcc/2 (linear) on a meter.
Substitutes
Reed switch (no power, but mechanical and slower), or a magnetoresistive/TMR sensor for higher sensitivity.