Reed Switch

Reed Switch 

Overview

A Reed Switch is a magnetically operated switch that opens or closes in the presence of a magnetic field.

Commonly used in:

• Door/window sensors

• Speed detection

• Robotics

• Security systems

Working Principle

• Inside the switch two thin ferromagnetic metal reeds sealed in a glass tube

• When a magnet comes close:

  • Reeds attract each other circuit closes (ON)

   

• When magnet moves away:

  • Reeds separate circuit opens (OFF)

   

Based on magnetic attraction (no power needed to operate)

Infographic Summary

REED SWITCH Function: Magnetic switch Power: Not required Output: Digital (ON/OFF) Type: Normally Open/Closed Operation: Contact-based Trigger: Magnetic field

Basic Connecti)

• ON by default, turns OFF near magnet

Changeover (SPDT)

• Switches between two contacts

Key Features

• Magnetic field detection

• No external power required

• Simple and reliable

• Compact and sealed

• Low power consumption

Applications

• Door/window alarm systems

• Bicycle speedometer

• Wheel rotation sensing

• Robotics limit switches

• Proximity detection

• Industrial automation

Interfacing

Compatible with:

• Arduino

• ESP32 / ESP8266

  (use pull-up resistor)

  Working Example

  Door Sensor System:

  • Door closed magnet near switch ON

  • Door open magnet away switch OFF alarm triggered

   

  Important Notes

  • Fragile (glass enclosure)

  • Limited switching current

  • Can wear out with very frequent switching

  • Sensitive to strong magnetic fields

   

  Reed Switch vs Hall Effect Sensor

  Perfect for simple, low-cost magnetic detection projects

• Use with pull-up resistor to avoid floating signals

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