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

The Modulo Reed Switch (KY-025), manufactured by Keys, is an electromechanical switch that operates in the presence of a magnetic field. It consists of two ferromagnetic contacts enclosed in a sealed glass tube. When a magnetic field is applied, the contacts close, allowing current to flow through the circuit. This component is widely used in applications requiring non-contact switching, such as proximity sensing, security systems, and magnetic field detection.

• Proximity sensors in industrial and consumer devices
• Door and window security systems
• Magnetic field detection in robotics
• Position sensing in automotive systems
• Home automation projects

The following table outlines the key technical details of the KY-025 Modulo Reed Switch:

The KY-025 Modulo Reed Switch has a 3-pin interface. The pinout is as follows:

1. Connect the Pins:

   • Connect the VCC pin to a 3.3V or 5V power source.
   • Connect the GND pin to the ground of your circuit.
   • Connect the Signal (S) pin to a digital input pin on your microcontroller or other logic circuit.

2. Adjust Sensitivity:

   • Use the onboard potentiometer to adjust the sensitivity of the reed switch. Turning the potentiometer clockwise increases sensitivity, while turning it counterclockwise decreases it.

3. Place a Magnet:

   • Position a magnet near the reed switch. When the magnetic field is strong enough, the switch will close, and the Signal (S) pin will output a HIGH signal.

• Magnet Placement: Ensure the magnet is placed within the sensitivity range of the reed switch for reliable operation.
• Debouncing: The reed switch may produce noise or bounce when switching states. Use a capacitor or software debouncing to stabilize the signal.
• Power Supply: Use a stable power supply to avoid erratic behavior.

Below is an example of how to use the KY-025 with an Arduino UNO to detect a magnetic field:

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

const int reedSwitchPin = 2; // Pin connected to KY-025 Signal pin
const int ledPin = 13;       // Built-in LED on Arduino

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 reed switch state

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

  delay(100); // Small delay for stability
}

1. Reed Switch Not Responding:

   • Cause: Magnet is too far from the switch.
   • Solution: Move the magnet closer to the reed switch or adjust the potentiometer to increase sensitivity.

2. Erratic Output:

   • Cause: Electrical noise or bouncing contacts.
   • Solution: Add a 0.1µF capacitor across the signal and ground pins or implement software debouncing.

3. No Output Signal:

   • Cause: Incorrect wiring or insufficient power supply.
   • Solution: Double-check the wiring and ensure the power supply voltage is within the specified range (3.3V to 5V).

4. Potentiometer Not Adjusting Sensitivity:

   • Cause: Potentiometer damaged or improperly adjusted.
   • Solution: Replace the potentiometer or ensure it is not turned beyond its limits.

Q1: Can the KY-025 detect all types of magnets?
A1: The KY-025 is sensitive to most common magnets, but the detection range and response depend on the strength of the magnetic field.

Q2: Can I use the KY-025 with a 3.3V microcontroller?
A2: Yes, the KY-025 operates within a voltage range of 3.3V to 5V, making it compatible with 3.3V microcontrollers like the ESP32.

Q3: How do I know if the reed switch is working?
A3: When a magnetic field is detected, the Signal (S) pin outputs a HIGH signal, which can be verified using an LED or a multimeter.

Q4: Is the KY-025 suitable for outdoor use?
A4: The KY-025 is not weatherproof. For outdoor applications, ensure it is enclosed in a protective casing to prevent damage from moisture or dust.