Mechanical Switches

Mechanical Switches are devices that turn ON and OFF the current flowing along a conductor such as a wire or track on a PCB, using mechanical mechanisms.

Picture 169. Animation of lever switch

Mechanical switches come in two basic types depending on the switching action. Permanent or Momentary.
Switches are also categorised by the arrangement of the switch contacts.

Permanent Mechanical Switches.

With the Permanent type, the switch changes from On to OFF (or OFF to ON) and remains permanently changed. Another switching action is necessary to change the switch back. Permanent Mechanical switches use either a hinged arm or sliding contacts.

Toggle, Rocker, Slide, Rotary and Key switches are examples.

A. Hinged Arm.

The simplest switch has a movable arm pivoted at one end moving between two positions, ON or OFF. When the switch is ON, a contact on the arm is touching a fixed contact allowing current to pass. When the switch is OFF the contacts are not touching.

Picture 170. Animation of lever switch

The arm is sprung so that it rapidly snaps open and close. The arm is moved by a Toggle or Rocker.

Picture 171. Picture of Toggle switch Picture 172. Picture of Rocker switch
Toggle Switch Rocker Switch

Switch Contact Arrangements

To control circuits, it is necessary to have different arrangements of switch contacts from the simple On/Off to a Double Pole, Double Throw reversing slide switch with a centre OFF.

Picture 173. Picture of St & DT rocker switch
Double Pole        Single Pole


The majority of switches are used to control one wire in the circuit, switching On and Off one current flow. These are called SINGLE POLE switches or SP.
Switches can be made that combine two separate switches in one housing switched with only one operation. These control two separate conductors in the circuit, switching ON and Off two current flows at exactly the same time. Theses are called DOUBLE POLE switches or DP.

The dotted line shows that the two arms operate together. In some circuit diagrams, the two parts of the switch are positioned in different parts and the dotted lines will show that they operate as one.

Picture 178. SP/DP ST/DT circuit diagrams


Perhaps the name comes from the arm being moved or thrown from one contact to another. Double Throw DT moves between two contacts. Single Throw ST only moves to one contact.
Double Throw Toggle switches also come with a centre OFF position. Look at the manufacturer's specifications for switches in a catalogue.

Picture 179. Amination of SP DT + off circuit diagram

B. Sliding Contact.

In this type of switch, a moving contact is made to slide over fixed contacts either in a straight line or in a rotary motion.

1. Slide Switches.

Picture 174. Animation of slide switch Picture 176. Picture of slide switch

Slide Switch contact arrangements.

Slide switches are supplied in three main contact arrangements.

Picture 180. Animation of slide switches

2. Rotary Switches.

Picture 175. Animation of rotary switch Picture 177. Picture of a rotary switch

Rotary Switch contact arrangements.

Picture 181. Animation of rotary 4 pole 3 way switch   Picture 182. Animated Interlocking push switch.
3 Pole 4 Way   4 Pole 3 Way

POLES = Number of Inputs.
WAYS = Also called Throws are the number of switched outputs.


3. Key Switch.

Picture 185. Picture of key switch

4. Tilt Switch.

Picture 191. Animation of tilt switch Picture 190. Picture of a tilt switch

Momentary Mechanical Switches

With the momentary type, a force has to be applied to change the switch from ON to OFF (or OFF to ON). When the force is removed, the switch immediately returns to its original position.
Push, Reed and Micro switches are examples.

1. Push Switch.

Picture 188. Animation of push switch
Picture 183. Picture of push switch   Picture 184. Picture of interlocking push switch
Push Switch   Interlocking Push Switch

2. Micro Switch.

Picture 189. Animation of micro switch Picture 186. Picture of a micro switch

3. Read switch.

Picture 192. Animation of reed switch Picture 187. Picture of a reed switch
Issue 30 - 20/2/03