Switches

Switches are the most basic electronic component. A switch creates a break (disconnection) in a circuit to stop the flow of current. The break has almost infinite resistance because in theory it should have as much resistance as the air between the gap in the connection. Switches are said to be open when there is a gap between the contractors inside of them that disallows the flow of current. On the other hand, a switch is said to be closed when the contractors are contacting one another which enables the flow of current within the circuit. A switch is always either open or closed although some switches can have additional connections that can be closed depending on the position of the switch.

Besides the simple type of switches that are only either open or closed (on or off) there are also many other configurations that that allow a switch to select one of several circuits depending on its position.


The simplest type of switch is the single pole single throw (SPDT). The SPDT switch has two terminals that are either connected or disconnected. Another type of switch is the single pole double throw (SPDT). SPDT switches can select one of two connections to turn on. Many times these switches will be labeled with the abbreviations NC, NO, and COM; these stand for normally open (NO), normally closed (NC) and common (COM). These are the normal connections that are the default state of the switch.