A reed switch is an electromagnetic switch that opens and closes in response to a magnetic field. It consists of two ferromagnetic contacts sealed within a small glass tube. When a magnetic field is applied, the contacts close, completing an electrical circuit. Once the magnetic field is removed, the contacts return to their open state.
Reed switches are widely used in various applications due to their simplicity, reliability, and low power consumption. Common use cases include:
This circuit is designed to control a water pump using a DC power source and a reed switch. The reed switch acts as a sensor that, when triggered, allows current to flow from the DC jack to the water pump, turning it on. There is no microcontroller or additional control logic, indicating that the pump operates directly in response to the state of the reed switch.
Open Project in Cirkit Designer
This circuit uses an Arduino UNO to monitor the state of a reed switch. When the reed switch is activated by a magnetic field, the Arduino turns on an onboard LED and outputs a message to the serial monitor. The reed switch is connected to the Arduino with an internal pull-up resistor on digital pin D2, and the LED is controlled via pin D13.
Open Project in Cirkit Designer
This circuit uses a Wemos D1 Mini microcontroller to monitor the state of multiple reed switches and control a WS2812 RGB LED strip. The microcontroller is powered by a 3xAA battery pack, and the reed switches are used to trigger different actions or lighting patterns on the LED strip.
Open Project in Cirkit Designer
This circuit consists of four reed switches, each controlling a different colored LED (green, blue, red, and orange). When a reed switch is activated, it completes the circuit, allowing current to flow from the Vcc to the corresponding LED, which then lights up. All LEDs share a common ground connection.
Open Project in Cirkit DesignerBelow are the key technical details of a typical reed switch. Note that specifications may vary depending on the manufacturer and model.
| Parameter | Value |
|---|---|
| Contact Form | SPST (Single Pole Single Throw) |
| Switching Voltage | 3V to 250V DC/AC |
| Switching Current | 10mA to 3A |
| Contact Resistance | 50 mΩ to 200 mΩ |
| Insulation Resistance | >10⁹ Ω |
| Operating Temperature | -40°C to +125°C |
| Response Time | 0.5 ms to 2 ms |
| Glass Tube Dimensions | 10 mm to 50 mm (length) |
Reed switches typically have two leads (pins) extending from the glass tube. These leads are the electrical contacts of the switch.
| Pin | Description |
|---|---|
| Pin 1 | Contact 1 (connects to the circuit) |
| Pin 2 | Contact 2 (connects to the circuit) |
Below is an example of how to use a reed switch with an Arduino UNO to detect the presence of a magnet.
// Reed Switch Example with Arduino UNO
// This code reads the state of a reed switch and turns on an LED when the switch is closed.
const int reedSwitchPin = 2; // Pin connected to the reed switch
const int ledPin = 13; // Pin connected to the onboard LED
void setup() {
pinMode(reedSwitchPin, INPUT_PULLUP); // Set reed switch pin as input with pull-up resistor
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 == LOW) { // Reed switch is closed (magnet present)
digitalWrite(ledPin, HIGH); // Turn on the LED
Serial.println("Magnet detected!");
} else { // Reed switch is open (no magnet)
digitalWrite(ledPin, LOW); // Turn off the LED
Serial.println("No magnet detected.");
}
delay(100); // Small delay to stabilize readings
}
Reed Switch Not Responding to Magnet
Switch Bouncing Causes Erratic Behavior
Reed Switch Breaks During Installation
False Triggering Due to Nearby Magnetic Fields
Q: Can a reed switch handle AC signals?
A: Yes, reed switches can handle both AC and DC signals, provided the voltage and current ratings are not exceeded.
Q: How do I increase the sensitivity of a reed switch?
A: Use a stronger magnet or a reed switch with a lower pull-in sensitivity rating.
Q: Can I use a reed switch in high-vibration environments?
A: Reed switches are sensitive to vibration, which may cause false triggering. Consider using a solid-state alternative like a Hall effect sensor in such environments.