41F bipolar Hall effect latch in a black TO-92 package, marked 41F over 551, with three straight leads

41F Bipolar Hall Effect Latch Sensor - TO-92, 4.5V to 24V

$0.59 NZD
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41F bipolar Hall effect latch in a black TO-92 package, marked 41F over 551, with three straight leads
  • 41F bipolar Hall effect latch in a black TO-92 package, marked 41F over 551, with three straight leads
  • Five 41F Hall effect latch sensors, the minimum order quantity, marked faces up
  • Front view of the 41F marked face with its three leads: pin 1 VCC on the left, pin 2 GND in the middle, pin 3 OUT on the right
  • 41F Hall sensor dimensions: 4.0mm wide, 3.0mm high and 1.5mm thick body, 1.27mm pin pitch, leads 14mm or longer
41F Bipolar Hall Effect Latch Sensor - TO-92, 4.5V to 24V
SKU: 41F-HALL-TO92

41F Bipolar Hall Effect Latch Sensor - TO-92, 4.5V to 24V

$0.59 NZD
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Minimum order quantity: 5

Easy 30-day returns · 12-month warranty

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The 41F is a bipolar Hall effect latch in a small three-pin TO-92 package, marked 41F and 551. A south pole facing the marked side switches the output on, and it stays on after the magnet moves away. Only a north pole switches it off again. That makes it ideal for counting alternating poles on a spinning ring magnet or rotor. It runs from 4.5V to 24V, so power it from 5V on an Arduino or ESP32, and give the output a pull-up.

Specifications

Model41F, marked 41F 551
Sensor typeBipolar Hall effect latch
Supply voltage4.5V to 24V DC
Output typeDigital, open collector, active low
Output currentUp to 20mA sink
SwitchingSouth pole sets it LOW, north pole resets it HIGH
Power-up stateUndefined until it sees a pole
Pull-upRequired, or use INPUT_PULLUP
Operating temperature-40°C to +85°C
PackageTO-92UA, about 4.0 x 3.0 x 1.5mm
Lead pitch1.27mm, leads 14mm or longer
PinoutMarked side facing you, legs down: 1 VCC, 2 GND, 3 OUT

Datasheets

Full technical datasheet PDF

Try it: present a pole to the sensor

What's in the box

5+
41F bipolar Hall effect latches, TO-92

Minimum order of 5, then any quantity you like. Supplied loose in an antistatic bag.

Great for

Counting RPM from a ring magnet with alternating poles
Reading the rotor position of a brushless motor
A magnetic on/off toggle that holds its state
An index mark on a rotating shaft or wheel
Fast edge counting on an interrupt pin
Contactless sensing in dusty or damp machinery

Wiring & getting started

  1. Hold it marked side facing you, legs down

    The pins run left to right: 1 is VCC, 2 is GND and 3 is OUT.

  2. Power it from 5V

    Connect VCC to 5V and GND to ground. 3.3V is below the 4.5V minimum, so use the 5V pin on an ESP32 too.

  3. Connect OUT with a pull-up

    Use a digital pin with pinMode(pin, INPUT_PULLUP), or fit 10k from OUT to your logic rail. On an ESP32, pull up to 3.3V so the pin never sees 5V.

  4. Set a known state at startup

    A latch powers up undefined. Pass a known pole past it before you trust the reading.

  5. Test both poles

    South on the marked face pulls OUT LOW and it holds. North releases it back HIGH.

Note: If the output turns on and never turns off, nothing is broken: a latch waits for the opposite pole. For an output that releases as soon as the magnet moves away, use the A3144 Hall switch instead.
Related guide Hall Effect Sensors Explained: Switch vs Latch vs LinearSwitch, latch or linear? A plain-English guide to picking the right hall effect sensor for your Arduino or ESP32 project, with wiring, code, and fixes for th...

Frequently Asked Questions

Answers to the questions buyers ask most.

It turned on and now it will not turn off. Is it faulty?
Almost certainly not. The 41F is a latch, and that is exactly how a latch behaves. A south pole switches it on and it holds that state after the magnet leaves. It only releases when a north pole comes past. If you wanted it to release when the magnet moves away, you want a switch like the A3144 instead.
What is the difference between this and the A3144?
The A3144 is a switch: on while a magnet is near, off when it leaves. The 41F is a latch: on with south, off with north, and it remembers in between. Same package, same wiring, completely different behaviour.
What is a latch actually good for?
Anything that spins past alternating poles. A ring magnet with north and south segments, a brushless motor rotor, or a wheel with magnets fitted in alternating orientation. Because the output only changes at a pole transition you get clean, unambiguous edges with no jitter around the release threshold, which makes RPM counting far more reliable at speed.
Why is my reading noisy or random?
The output is open collector, so it can only pull down to ground and needs a pull-up to sit high. Fit a 10k from OUT to your logic rail, or use pinMode(pin, INPUT_PULLUP) in your sketch. Without it the pin floats and reads as noise. When it does trigger, the pin reads LOW.
What state is it in at power-up?
Undefined until it sees a pole. A latch has no default, so on first power-up it could be either state depending on residual magnetism. If your logic depends on knowing the starting state, sweep a known pole past it during startup, or use a switch instead.
Will it work on a 3.3V ESP32?
Yes, if you power it from 5V. It needs 4.5V minimum, so 3.3V is not enough for the supply. The open collector output means you can still pull up to 3.3V, so the ESP32 pin only ever sees 3.3V logic.
Can I run it straight off 12V or 24V?
Yes, it takes anything from 4.5V up to 24V. Just pull the output up to your microcontroller's logic rail rather than the supply rail, so the input pin never sees more than it is rated for.

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