US1881 bipolar Hall effect latch in a flat TO-92 (UA) package, marked U18, with three leads

US1881 Bipolar Hall Effect Latch Sensor - TO-92, 3.5V to 24V

$0.79 NZD
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US1881 bipolar Hall effect latch in a flat TO-92 (UA) package, marked U18, with three leads
  • US1881 bipolar Hall effect latch in a flat TO-92 (UA) package, marked U18, with three leads
  • Five US1881 Hall effect latch sensors, the 5-unit minimum order
  • US1881 marked sensing face straight on, with the three leads VDD, GND and OUT from left to right
  • US1881 TO-92UA dimensions: 4.0mm wide, 3.0mm high and 1.5mm thick body, 1.27mm pin pitch, leads 14mm or longer
US1881 Bipolar Hall Effect Latch Sensor - TO-92, 3.5V to 24V
SKU: US1881-HALL-TO92

US1881 Bipolar Hall Effect Latch Sensor - TO-92, 3.5V to 24V

$0.79 NZD
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Buy more, pay less Prices shown are per unit. Add enough of this item and the lower rate applies on its own at checkout. There is no code to enter and you do not need to buy a pack. Choosing a tier here just sets the quantity for you. Larger quantities go out in the same bag, so packing, handling and postage cost us less per unit. We pass that saving straight on to you, so you can buy more for less.

Minimum order quantity: 5

Easy 30-day returns · 12-month warranty

Add $66.00 for Free Urban delivery ($88.00 for Rural)
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The US1881 is a bipolar Hall effect latch in a small three-pin TO-92 package, marked U18 on the front. 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. It runs from 3.5V to 24V, the lowest supply minimum of our Hall latches, so it suits 5V, 12V and 24V projects alike. On a 3.3V board, power it from 5V and pull the output up to 3.3V.

Specifications

ModelUS1881, marked U18 plus a date code
Sensor typeBipolar Hall effect latch
Supply voltage3.5V to 24V DC
Supply current5mA max
Output typeDigital, open drain, active low
Output currentUp to 20mA sink
SwitchingSouth pole sets it LOW, north pole resets it HIGH
Switch pointsWithin 9.5mT (95 gauss) of either pole
Power-up stateUndefined until it sees a pole
Operating temperature-40°C to +85°C
PackageTO-92 flat (UA), about 4 x 3 x 1.5mm, 1.27mm lead pitch
PinoutMarked side facing you, legs down: 1 VDD, 2 GND, 3 OUT

Datasheets

Full technical datasheet PDF

Try it: present a pole to the sensor

What's in the box

5+
US1881 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
Sensing straight off a 12V or 24V supply
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 VDD, 2 is GND and 3 is OUT.

  2. Power it from 5V or more

    Connect VDD to 5V (or anything up to 24V) and GND to ground. 3.3V is below the 3.5V minimum, so use the 5V pin on an ESP32 too. A 100nF capacitor across VDD and GND close to the sensor helps on long leads.

  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. To compare all our Hall sensors, see the switch vs latch vs linear guide.
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?
No. The US1881 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 want an output that releases as soon as the magnet moves away, use a switch such as our A3144 instead.
Will it work with a 3.3V board like an ESP32?
Yes, if you power it from 5V. The supply minimum is 3.5V, so a 3.3V rail is not enough. The output is open drain, so pull it up to 3.3V (or use INPUT_PULLUP) and the input pin only ever sees 3.3V.
How is it different from your 41F latch?
Both are bipolar latches with the same pinout and the same behaviour. The US1881 runs from 3.5V where the 41F needs 4.5V, so pick the US1881 when your supply might sag below 4.5V. On a steady 5V, 12V or 24V supply either one will do the job.
Can I run it straight off 12V or 24V?
Yes, anything from 3.5V up to 24V. 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.
Why is my reading noisy or random?
The output is open drain, so it can only pull down to ground and needs a pull-up to sit high. Fit 10k from OUT to your logic rail, or use pinMode(pin, INPUT_PULLUP). Without it the pin floats and reads as noise. When the sensor is on, the pin reads LOW.
What state is it in at power-up?
Undefined until it sees a pole. If your code depends on the starting state, pass a known pole past it during startup, or read it once a magnet has gone by.
Can it drive an LED directly?
Yes, as a low-side switch. Run the LED and a series resistor from your supply to OUT, and size the resistor so the current stays at 20mA or less. The LED lights while the sensor is latched on.
How strong a magnet does it need?
It switches at up to 9.5mT (95 gauss) of either pole, measured on the marked face. A small neodymium magnet brought close to the marked face is normally enough. Remember it needs a south pole to switch on and a north pole to switch off, so a ring magnet with alternating poles or two magnets fitted opposite ways round works best.

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