---
tags: [electronics]
created: Monday, September 09, 2024
---

# Relays

A relay is an electrically operated switch.

It uses an electromagnet to mechancially operate a switch. A switch in one
circuit can be used the trigger the operation of another circuit.

## Core components

- electromagnet
  - a coil of wire around an iron core
- armature
  - a movable magnetic strip
- contacts
  - electrical connections that can be open or closed
- spring
  - returns the armature to its resting position when not energised

## Operation

![Operation of a relay](../img/relay.gif)

Current flows through the electromagnet which creates a magnetic field. This
field attracts the armature which then moves to open or close the contacts. When
the current stops, this returns the armature to its original position.

## Usage

During the
[electro-mechanical era of computing](The_History_of_Computing_Swade.md) they
were used as precursors to vacuum tubes (and later, transistors) to implement
logic gates. While they were superseded in this domain, they are still used in
industrial control systems and automobiles.
