Arduino Hall Effect Sensor: How to Detect Magnetic Fields

In this guide, you’ll learn how to set up an Arduino Hall effect sensor, specifically the US1881, to detect magnetic fields. This can be useful for projects where you need to find the RPM of a motor or other movements in a machine.

Parts Needed

Schematic Diagram

Connect the VDD pin of the US1881 Hall effect sensor to 5V on the Arduino and the GND pin to GND.

This sensor uses an open-drain output, which means that you need a pull-up resistor to 5V in order to read out any value from it. The value of the resistor isn’t crucial. 1k to 100k will work fine.

The capacitor across the output stabilizes the output but could be skipped.

Arduino Hall effect sensor circuit diagram

Here’s an example of how you can connect this circuit to a breadboard:

How to connect the Arduino Hall effect sensor circuit on a breadboard

Arduino Hall Effect Sensor Test Code

To test the Hall effect sensor, you need to read the output pin, which is connected to Arduino digital pin 2. So basically all you need code-wise to read out the value is hallSensorState = digitalRead(D2);

Here’s the complete code to test your sensor:

const int hallSensorPin = 2;  // Hall Effect sensor connected to digital pin 2
int hallSensorState;          // Variable to store the state of the sensor

void setup() {
  Serial.begin(9600);                // Start serial communication at 9600 baud
  pinMode(hallSensorPin, INPUT);     // Set the Hall Effect sensor pin as an INPUT

void loop() {
  hallSensorState = digitalRead(hallSensorPin); // Read the state of the sensor

  // Check if the sensor is detecting a magnetic field
  if (hallSensorState == HIGH) {
    Serial.println("Magnetic field detected!"); // If yes, print this message
  } else {
    Serial.println("No magnetic field detected."); // If no, print this message

  delay(1000); // Wait for 1 second before the next read

Step-by-Step Instructions

  1. Assemble the circuit as shown in the breadboard layout and schematic diagram above.
  2. Connect the Arduino to your computer with a USB cable.
  3. Open the Arduino IDE and copy the example code into a new sketch.
  4. Upload the sketch to your Arduino board.
  5. Open the Serial Monitor to view the output messages. You should see “Magnetic field detected!” when a magnet is near the sensor, and “No magnetic field detected.” when it’s not.

If you want to learn more details about this sensor, check out its datasheet.

Troubleshooting Tips

  • Ensure all connections are secure and match the schematic.
  • If the sensor always reads “HIGH,” check for any magnetic sources nearby, including the magnet inside the breadboard power rails.
  • If the sensor does not detect a magnetic field, ensure the magnet is close enough to the sensor.


Now you know how to detect magnetic fields using a Hall Effect sensor with your Arduino. This setup can be used as a magnetic door sensor, for RPM counting, or in any project requiring magnetic field detection.

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