Switches

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting thecurrent or diverting it from one conductor to another. The most familiar form of switch is a manually operatedelectro mechanical device with one or more sets of electrical contacts. Each set of contacts can be in one oftwo states: either "closed" meaning the contacts are touching and electricity can flow between them, or"open", meaning the contacts are separated and the switch is no conducting. The mechanism actuating thetransition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on"or "off") or "momentary" (push-for "on" or push-for "off") type. A switch may be directly manipulated by ahuman as a control signal to a system, such as a computer keyboard button, or to control power flow in acircuit, such as a light switch. Automatically operated switches can be used to control the motions ofmachines, for example, to indicate that a garage door has reached its full open position or that a machinetool is in a position to accept another work piece. Switches may be operated by process variables such aspressure, temperature, flow, current, voltage, and force, acting as sensors in a process and used toautomatically control a system. For example, a thermostat is a temperature-operated switch used to controla heating process. A switch that is operated by another electrical circuit is called a relay. Large switchesmay be remotely operated by a motor drive mechanism. Some switches are used to isolate electric powerfrom a system, providing a visible point of isolation that can be pad-locked if necessary to preventaccidental operation of a machine during maintenance, or to prevent electric shock.Surface mounted devices (SMD) are active and passive electronic components without Conventionalconnecting wires.The SMD components will be placed on the "solder side" of the PCB and their metal caps Soldered to thecopper pads of the PCB. Therefore both layers of the PCB could be used as active areas. A thickness ofPCBs used for SMD is between 0.8 and 1.00 mm. Historically roots of SMD are hybrid circuits on theceramic substrates (middle of seventies) but a huge Industrial applications of SMD started on a begineighties.