Some common switches are shown on this information sheet. Basically switches bring contacts together in different ways but they do the same switching job.

Typical Switch Symbols

This switch is available in different forms. They provide limited security as a key is required to ‘switch’ them on and off.

This is a thin glass tube that contains two thin strips of metal (the reeds). When a magnet is brought close to the glass tube, the reeds move together and make contact and the switch is turned on. The reeds open again when the magnet is removed. Reed switches are common in alarm systems, for example, in door frames. When the door is closed the magnet keeps the switch on. When the door is opened the alarm system senses the broken contact and goes off.

Micro-switches can be very small. Usually they include a small arm which when pressed clicks. They are very useful and can be found on many machines - used a safety switches. For example, if the 'lid' of a drilling machine is opened to change the pulley speeds, a micro-switch is released ensuring that all power is turned off. These switches can be very useful in school projects

One of the most common types of tilt switch uses a ‘blob’ of mercury in a small tube. When the tube is tilted the mercury runs down and forms a bridge across the two contacts turning the switch on. This type of switch is used in warning systems that alert people to an excessive angle of tilt, e.g. for drivers of farm vehicles.
 

This is a soft flexible switch available in many sizes. It consists of two flexible conductive foil sheets separated by a thin felt, paper or foam layer. If pressure is applied the conductive surfaces touch and the switch is ‘on’