Electrical Controls
Good electrical circuits have control devices that help ensure that the right amount of electricity flows to the right places at the right time. There are many electrical control devices that have been replaced by electric controls but below are several that are still commonly used. Electronics Components are generally combinations of the basic components listed below.
Control Devices
Resistors - a passive two-terminal electrical component that implements electrical resistance as a circuit element.They act to reduce current flow, and, at the same time, act to lower voltage levels within circuits. The electrical function of a resistor is specified by its resistance: common commercial resistors are made over a range of more than nine types of magnitude. The cheap value of the resistance will fall within a manufacturing tolerance. Some examples would be high-power wire wound resistors used for dynamic braking on an electric railway car, or Laser Trimmed Precision Thin Film Resistor Network from Fluke, used in the Keithley DMM7510 multimeter or even,A carbon resistor printed directly onto the SMD pads on a PCB. Inside a 1989 vintage Psion II Organiser ; Although this technique is more common on hybrid PCB modules, it can also be used on standard fibreglass PCBs. http://en.wikipedia.org/wiki/Resistor
Potentiometers - an adjustable resistor which consists of a wiper that slides across a resistive strip to deliver an increase or decrease in resistance. The level of resistance will determine output of current to the circuit,The humble potentiometer (or pot, as it is more commonly known) is a simple electro-mechanical transducer. It converts rotary or linear motion from the operator into a change of resistance, and this change is (or can be) used to control anything from the volume of a hi-fi system to the direction of a huge container ship. The taper (also called "law") of a pot is important. We need not worry with trimpots, since they are almost always linear, and I do not know of a supplier of anything other than linear trimpots. For all panel pots, we must be aware of the use the pot will have, and select the correct type accordingly. The slide-wire potentiometer was invented by Johann Christian Poggendorff (1796-1877) in 1841. In addition to his work with electricity, he was the editor of the Annalen de Physik und Chemie from 1824 to 1876, and his biographical volumes of scientists have become standards and are still being published http://en.wikipedia.org/wiki/Potentiometer
Switches - a electrical component that can break an electrical circuit. It interrupts the current from one conductor to another. It is used so that when it is shifted one way it will turn something on or off and in the other direction it will do the opposite. It gives you the ability to change a light, or turn on power in general, from a farther distance than directly from the source of power. The switch was invented by John Henry Holmes in 1884 in the Sheildfield district of Newcastle. http://en.wikipedia.org/wiki/Switch
Capacitors A capacitor is an electrical component that stores energy in an electric field. They are usually made up of two plates and an insulator. They are widely used in electrical devices due to the large amount of energy they can store in a relatively small area. One of the first capacitors to be made was made late in 1745, by Ewald Georg von Kleist. http://en.wikipedia.org/wiki/Capacitor
Diodes - a two-terminal electronic component with asymmetric conductance. It has a low resistance (ideally zero) to current in one direction. A high resistance (ideally infinite) in the other. A semiconductor diode is the most common type today. A crystalline piece of semiconductor material with a p-n junction connected to two electrical terminals. The discovery of crystals' rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whiskers diodes were developed around 1906. There have been many changes to the diode over the years. Today most diodes are made of silicon but other semiconductors such as selenium or germanium are sometimes used.
Transistors - an electronic devise that can work as a switch or amplifier. As a switch the transistor use a signal sent to the base to turn on or off the connection between the collector and emitter. The signal can be a very small positive or negative charge (depending on the type of transistor). The current flowing through the collector and emitter can be a much larger voltage and amperage. This is how a transistor can amplify a signal. This is how a transistor radio was able to take very week radio signals and play the music with a higher volume.
Transistor - http://en.wikipedia.org/wiki/Transistor
