How to Use KY-025 Modulo Reed Switch: Examples, Pinouts, and Specs

The KY-025 Modulo Reed Switch, manufactured by Arduino (Part ID: HH), is a versatile sensor module designed to detect magnetic fields. It operates using a reed switch, a small mechanical switch that closes its contacts when exposed to a magnetic field. This module is widely used in applications such as door and window sensors, security systems, and other projects requiring magnetic field detection. Its simplicity and reliability make it a popular choice for hobbyists and professionals alike.

The KY-025 Modulo Reed Switch has the following technical specifications:

• Operating Voltage: 3.3V to 5V
• Output Type: Digital and Analog
• Dimensions: 32mm x 14mm x 10mm
• Detection Range: Up to 10mm (depending on the strength of the magnet)
• Operating Temperature: -40°C to +85°C
• Power Consumption: Low power consumption suitable for battery-powered applications

The KY-025 module has three pins, as described in the table below:

1. Wiring the Module:

   • Connect the VCC pin to the 5V pin on your microcontroller (e.g., Arduino UNO).
   • Connect the GND pin to the ground (GND) of your microcontroller.
   • Connect the Signal (S) pin to a digital input pin (e.g., D2) or an analog input pin (e.g., A0) on your microcontroller.

2. Magnetic Field Detection:

   • When a magnet is brought near the reed switch, the contacts inside the switch close, and the module outputs a signal.
   • The digital output pin will go HIGH (1) when a magnetic field is detected and LOW (0) otherwise.
   • The analog output pin provides a voltage proportional to the strength of the magnetic field.

3. Example Circuit:

   • Place the KY-025 module on a breadboard.
   • Use jumper wires to connect the module to your microcontroller as described above.
   • Optionally, connect an LED to the digital output pin to visually indicate magnetic field detection.

• Avoid exposing the module to strong vibrations or shocks, as this may damage the reed switch.
• Ensure the magnet used is within the detection range of the module for reliable operation.
• Use pull-up or pull-down resistors if necessary to stabilize the digital output signal.
• Keep the module away from strong electromagnetic interference (EMI) sources to prevent false triggering.

Below is an example code snippet to use the KY-025 Modulo Reed Switch with an Arduino UNO:

// KY-025 Reed Switch Example Code
// Connect the Signal pin to digital pin 2 on the Arduino UNO
// Connect VCC to 5V and GND to GND

const int reedSwitchPin = 2; // Pin connected to the KY-025 Signal pin
const int ledPin = 13;       // Built-in LED pin for visual indication

void setup() {
  pinMode(reedSwitchPin, INPUT); // Set reed switch pin as input
  pinMode(ledPin, OUTPUT);       // Set LED pin as output
  Serial.begin(9600);           // Initialize serial communication
}

void loop() {
  int reedState = digitalRead(reedSwitchPin); // Read the state of the reed switch

  if (reedState == HIGH) {
    // If magnetic field is detected, turn on the LED
    digitalWrite(ledPin, HIGH);
    Serial.println("Magnetic field detected!");
  } else {
    // If no magnetic field is detected, turn off the LED
    digitalWrite(ledPin, LOW);
    Serial.println("No magnetic field detected.");
  }

  delay(500); // Wait for 500ms before reading again
}

1. The module does not detect the magnet:

   • Ensure the magnet is within the detection range of the reed switch.
   • Verify that the module is properly powered (3.3V or 5V).
   • Check the wiring connections for loose or incorrect connections.

2. False triggering or unstable output:

   • Use a pull-up or pull-down resistor to stabilize the digital output signal.
   • Keep the module away from sources of electromagnetic interference (EMI).

3. No output signal:

   • Confirm that the reed switch is not physically damaged.
   • Test the module with a multimeter to ensure the reed switch closes when a magnet is nearby.

Q: Can the KY-025 module detect the polarity of a magnet?
A: No, the KY-025 module cannot detect the polarity of a magnet. It only detects the presence of a magnetic field.

Q: Can I use the KY-025 module with a 3.3V microcontroller?
A: Yes, the KY-025 module is compatible with both 3.3V and 5V microcontrollers.

Q: What type of magnet should I use with the KY-025 module?
A: Any small neodymium or ferrite magnet should work, as long as it is within the detection range of the reed switch.

Q: Is the KY-025 module suitable for outdoor use?
A: The module is not weatherproof. If used outdoors, it should be enclosed in a protective casing to prevent damage from moisture or dust.