Reed Switch Hookup Guide

Contributors: jimblom
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Reed switches are magnetically-actuated electrical switches (not magically-actuated, though it seems that way sometimes). When the body of the switch is exposed to a magnetic field -- like a magnet or even a strong electrical current -- two ferrous materials inside pull together, the connection closes, and current can flow. In absence of a magnetic field, the switch opens as does the circuit it's a part of.

Reed Switch

Reed Switch


There are all sorts of creative applications for reed switches. They're perfect for any projects that require non-contact control. A magnetic door switch, for example, is just a dressed up reed switch and a mating magnet -- by keeping both parts of the switch separate, the door can open and close freely (and maintain its regular duties as a door). The anemometer in our weather meter combines a number of reed switches, which all open and close in order as the wind blows; count the time between switch closures to determine the wind speed.

Suggested Materials

This tutorial serves as a quick primer on reed switches and demonstrates how to hook them up and use them. Beyond the switch itself, the following materials are recommended:

Magnet -- You'll need something to actuate the reed switch, and this small magnet should fit the bill.

Arduino Uno -- We'll be using a digital pin on the Arduino to read the state of the switch. Any Arduino-compatible development platform -- be it a RedBoard, Pro or Pro Mini -- can substitute.

Breadboard and Jumper Wires -- With it's legs properly bent, the reed switch is breadboard-compatible. We'll use the breadboard as an intermediary between reed switch and jumper wires, which will connect the switch to an Arduino.

Breadboard - Self-Adhesive (White)

Breadboard - Self-Adhesive (White)

Jumper Wires Standard 7" M/M - 30 AWG (30 Pack)

Jumper Wires Standard 7" M/M - 30 AWG (30 Pack)

Magnet Square - 0.25"

Magnet Square - 0.25"


SparkFun RedBoard - Programmed with Arduino

127 Retired

Suggested Reading

Read switches are a fun and easy-to-use component for beginners, but there are still a few basic electronics concepts you should be familiar with. If any of these tutorial titles sound foreign to you, consider skimming through that content first.

Pull-up Resistors

A quick introduction to pull-up resistors - whey they're important, and how/when to use them.

How to Use a Breadboard

Welcome to the wonderful world of breadboards. Here we will learn what a breadboard is and how to use one to build your very first circuit.

What is an Arduino?

What is this 'Arduino' thing anyway? This tutorials dives into what an Arduino is and along with Arduino projects and widgets.

Button and Switch Basics

A tutorial on electronics' most overlooked and underappreciated component: the switch! Here we explain the difference between momentary and maintained switches and what all those acronyms (NO, NC, SPDT, SPST, ...) stand for.