Switches

Switch Basics
A switch is often to turn something on or off. In the simplest case it is just a wire that is connected or not. Unplugging an appliance is one way to switch it off. A switch is usually a mechanical device where some sort of handle connects or disconnects conductors inside the switch. Another way of thinking of a switch is that it is like a resistor that sometimes has infinite resistance and sometimes has 0 resistance. A computer keyboard is made of a large number of switches. Some switches stay in the on or off position, others only stay on or off while you switch them, these are called momentary switches. A light switch is normally not momentary, a doorbell switch normally is momentary.

Uses:
 * On Off control
 * Range change, as in a meter
 * Data input

Links
 * Switch From Wikipedia,the free encyclopedia ( inc. Schematic and Picture )
 * Switches
 * Switch Terminology _P_T - SPST - SPDT - DPST - DPDT - 3PDT - ....

Relays
A Relay is a switch that is turned on and off by an electro-magnet ( actually there are new forms that do not use an electro-magnet ). Like other switching devices it allows a small amount of power to control a large amount of power. A nice feature of relays is that there is no electrical connection between the control circuit and the circuit connected to the switch. ( this is called electrical isolation ). They are often used to let low power digital circuits control normal 110v power in a home.

Uses:
 * Turn on several circuits with one control circuit.
 * Control motors.
 * Isolate a low voltage circuit from power line.
 * Reverse current ( double pole double throw relay )

Links


 * [[Image:Main-G5Q-14.jpg|69px|Relays]] Relays - Use these to control large power sources that a microcontroller cannot do alone
 * Relay From Wikipedia, the free encyclopedia
 * Controlling Big, Mean, Devices
 * Relays
 * Maximizing the Life Span of Your Relays]
 * Driving_Large_Loads_with_the_Arduino
 * Tyco Electronics Application Notes