The Mini Reed Switch Module uses a sensor that reacts to a magnetic field. It includes a 10K ohm resistor and a small switch reed switch actuated by a magnetic field.

This Mini Reed Switch Module activates a switch closure when exposed to a magnetic field and remains open without a magnetic field. In the test code below, the built-in LED on pin 13 flashes if the sensor is closed. A magnet must be near the sensor to close the switch.

Test Code

// Example code for sensor KY021
// More info on http://tkkrlab.nl/wiki/Arduino_KY-021_Mini_ magnetic_reed_modules

int Led = 13; // define LED Interface
int buttonpin = 3; // define the Reed sensor interfaces
int val; // define numeric variables val

void setup() {
pinMode(Led, OUTPUT); // define LED as output interface
pinMode(buttonpin, INPUT); // output interface as defined Reed sensor
}

void loop() {
val = digitalRead(buttonpin); // digital interface will be assigned a value of 3 to read val

// When the Reed sensor detects a signal, LED flashes
if (val == HIGH) {
digitalWrite(Led, HIGH);
}
else {
digitalWrite(Led, LOW);
}
}