Relay

 

An electrically operated switch, for example a 9V battery circuitconnected to the coil can switch a 230V AC mains circuit.NO = Normally Open, COM = Common, NC = Normally Closed.

ResistorsComponent Circuit Symbol Function of Component

Resistor 

 

A resistor restricts the flow of current, for example to limit the currentpassing through an LED. A resistor is used with a capacitor in a timingcircuit.Variable Resistor (Rheostat)

 

This type of variable resistor with 2 contacts (a rheostat) is usually usedto control current. Examples include: adjusting lamp brightness,adjusting motor speed, and adjusting the rate of flow of charge into acapacitor in a timing circuit.Variable Resistor (Potentiometer)

 

This type of variable resistor with 3 contacts (a potentiometer) is usuallyused to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal.Variable Resistor (Preset)This type of variable resistor (a preset) is operated with a smallscrewdriver or similar tool. It is designed to be set when the circuit ismade and then left without further adjustment. Presets are cheaper thannormal variable resistors so they are often used in projects to reducethe cost.

CapacitorsComponent Circuit Symbol Function of Component

Capacitor 

 

A capacitor stores electric charge. A capacitor is used with a resistor ina timing circuit. It can also be used as a filter, to block DC signals butpass AC signals.Capacitor,polarized

 

A capacitor stores electric charge. This type must be connected thecorrect way round. A capacitor is used with a resistor in a timingcircuit. It can also be used as a filter, to block DC signals but pass ACsignals.Variable Capacitor 

 

A variable capacitor is used in a radio tuner.Trimmer Capacitor This type of variable capacitor (a trimmer) is operated with a smallscrewdriver or similar tool. It is designed to be set when the circuit ismade and then left without further adjustment.

DiodesComponent Circuit Symbol Function of Component

Diode

 

A device, which only allows current to flow in one direction.LEDLight Emitting Diode

 

A transducer, which converts electrical energy to light.