Name	Symbol	Picture
AA Battery
PP3 Battery

What they are:

Batteries are self contained sources of electrical energy. There are five types :

	Zinc-Carbon : These are the most basic and inexpensive batteries.
	Alkaline : These are chemically different and more expensive but they last longer.
	Rechargeable : these are often referred to as 'Nicads' because they are based on the metals nickel and cadmium.
	Mercury Cells : These are the very small cells used in watches, calculators and small electronic games.
	Lithium Batteries : These are usually small and expensive but have a long shelf life. They are used as battery back-up in computers and other devices.

What they Do

Convert chemical energy into electrical energy.

Where they can be found

	In almost all portable electrical and electronic devices.
	Cordless drills and other equipment.

Why we use them

To supply power for most of our school projects.

Things to watch out for...

	Alkaline cells should never be mixed with other types.
	Mercury cells are toxic and should be disposed of safely.
	Nicad cells have a very low internal resistance. If they are short circuited (by keys or coins in your pocket for example) they could burn you badly.

  Bulbs

Name	Symbol	Picture
Filament Bulb

 

Filament bulbs convert electrical energy into light. When current passes  through the filament it becomes white hot or incandescent and gives out  light (as well as heat).

	Filament bulbs are commonly used for domestic lighting.
	Torches
	Models and Toys.

	To provide a visible output from a circuit (as in a road warning lamp)
	To provide a light source (as in a light beam for a light sensor)

	Some bulbs cannot be driven directly by some IC's check the current rating  carefully.
	Filament bulbs get very hot during operation. They should not come into contact with  plastic surfaces.
	They can be useful as sources of heat when testing a thermistor circuit.
	Before choosing a filament bulb consider carefully :

	Its physical size
	The shape of the glass bulb
	The type of socket or fitting required for connection to your circuit.

Its maximum voltage/current/wattage

  Capacitors

Name	Symbol	Picture
Ceramic Capacitor
Polyester Capacitor
Electrolytic Capacitor

 

What they are

A capacitor consists of two metal plates or metal films, seperated by an insulator. In  larger capacitors these are in the form of long ribbons wound into a tight cylinder

Capacitors store charge for a period of time. A large capacitor, when charged, can  supply enough current to run an LED for a few seconds

	Most electronic circuits.
	Radios, televisions and calculators.

	To provide a time delay.
	To smooth out unwanted variations in voltage.
	To keep something 'on' for a few seconds after a circuit is switched off.

Although most small capacitors can be connected either way round in a circuit. Some  larger ones (Electrolytic or Tantalum capacitors for example) must be connected the  right way round in a circuit. The -ve terminal is usually marked.

Name	Symbol	Picture
Diode

 

What they are

A diode is a component that allows current to pass in one direction only.

	They are usually used to prevent current flowing in a particular direction.
	Zener diodes can be used to control voltage.

Most electronic circuits.

 

	Protect Transistors against reverse voltages.
	In power supplies to provide a DC voltage.
	Provide a constant voltage (using a zener diode).
	Protect a battery driven circuit from reverse polarity.

Choose a diode which can handle the maximum current and voltage used or produced  by your circuit.

 

  Light Emitting Diodes (LED's)

Name	Symbol	Picture
Light Emitting diode

 

What they are

An LED (light emitting diode) is a special form of diode that can give out light when  current passes through it.

LED's are used mainly as low current light indicators.

	In a vast range of electronic appliances
	To indicate an on/off situation.
	To indicate volume using a bank of LED's (where the louder the volume the more LED's  are lit up).

 

As a low cost output indicator for many projects.

	LED's must be connected the right way round in a circuit.
	An LED must have a resistor connected in series or it wll be damaged.

 

  Resistors

Name	Symbol	Picture
Resistor

 

What they are

Fixed resistors are components used for regulating current and setting voltage levels in  circuits.

Resistors restrict current flow and the extent to which they do this is measured in ohms (). A 1ohm resistor is almost a normal conductor whilst a 10 Megohm resistor is  almost an insulator.

Fixed resistors are found in almost all electronic circuits.

	To regulate current flow.
	To provide different voltages (when used as potential dividers)

	As with most manufactured items resistors are made within a tolerance. The actual  resistance value of some resistors can be as much as 20% larger or 20% smaller than the coloured bands might suggest.
	Resistors are too small for their value to be printed on them so they are marked with  coloured bands.
	When current passes through a resistor heat is produced. Larger resistors have a  greater surface area and are able to lose heat more easily. For this reason resistors are available in a variety of sizes. Normally we use .25 watt resistors but you may need  larger resistors if high currents are involved.

 

  Variable Resistors or Potentiometers

Name	Symbol	Picture
Preset
Potentiometer

 

What they are

A variable resistor is a resistor whose resistance can be varied by turning a spindle or  moving a slider

	Resist current flow.
	Divide a potential.

	Volume control on radio's etc. (spindle type)
	Graphic Equlasier (slider type)

	As a potential divider.
	To provide adjustment in time delay circuits etc.

	Some variable resistors are linear while others are logarithmic. You will normally use  linear variable resistors. Logarithmic types are normally only used for volume controls.
	Most variable resistors have three legs or solder tags. The resistance between the two  outer legs is fixed at the value printed on the side or base. The resistance between the  wiper and either of the outside tags can be varied.
	A smaller version for mounting on PCB's is called a PRESET.

 

  Transistors

Name	Symbol	Picture
FET Transistor
NPN Transistor

 

What they are

A transistor is a component that controls current flow in a circuit. Most transistors  used in school belong to the bipolar family. The word Bipolar refers to the way they are  made.

A small current supplied to the base leg (terminal) controls a larger current flow between the collector and emitter legs. Transistors are either used as electronic switches or as  current amplifiers.

In almost all electronic circuits which control how something works.

To enable sensors to control the operation of lamps, motors, relays etc.

	Transistors are normally identified by numbers printed on their case.
	The three legs must be connected the right way round in a circuit. Some transistors have  small tabs which enable you to identify the emitter. Others are not so easy and you may  need to consult a data sheet, but there is always a method of identifying which leg is which.
	The maximum safe collector current Ic(max) should not be exceeded. (Ic means collector  current)
	The safe working voltage Vceo (max) should also not be exceeded. (Vceo means voltage  across collector/emitter tags)
	The difference between the base current and the collector/emitter current is known as the  gain (hfe). The gain quoted can only be approximate and you will usually see two figures  quoted i.e. hfe 110-800. This means that the gain will be somewhere between these two  figures.

 

  Thyristor

Name	Symbol	Picture
Thyristor

 

What they are

A thyristor is a component thast controls current flow in a circuit.

A small momentary trigger current supplied to the gate of a thyristor, causes a much larger  current to flow between the anode and cathode. This current continues to flow, even when the trigger current is removed. Unlike a transistor which turns off if the base current is removed, thyristors remain "on" and are said to be 'latched'.

Thyristors are commonly used in alarm systems where a warning sound or signal needs to  continue after the alarm has been triggered.

We can use thyristors in alarm circuits or in any situation where a single event needs to be recorded.

	The maximum supply voltage - this should never be exceeded.
	The maximum anode/cathode current - this should never be exceeded.
	The trigger current - a series resistor should be used to ensure this is not exceeded.

 

  Light Dependent Resistor (LDR)

Name	Symbol	Picture
Light Dependent Resistor

 

What they are

The light dependent resistor is a type of resistor whose resistance changes according to the  amount of light falling on it.

LDR's act as sensors in circuits designed to respond to changing light conditions.

	In alarm systems
	Automatic street lighting
	To automatically increase the brightness of digital displays during daylight.

As light sensors in automatic circuits.

	They have a high resistance in darkness (approx 100K) and a low resistance in bright light  (approx 100 ohms).
	Best used as part of a potential divider.
	They react quite slowly.

 

  Thermistor

Name	Symbol	Picture
Bead Thermistor

 

What they are

A resistor whose resistance changes according to its temperature.

Thermistors act as sensors in circuits designed to respond to changes in temperature. The resistance of most thermistors falls as the temperature rises.

	Most electronic circuits designed to respond to heat.
	Automatic electronic ovens.
	Motor cutout circuits.
	Ice detectors

To measure temperature.

Thermistors can be purchased to operate within a given temperature range.

Name	Symbol	Picture
S.P.D.T Relay
S.P.S.T Relay

Relays are special switches operated by an electromagnet.

Relays enable one electrical circuit to switch a second electrical circuit without an electrical connection between the two.

	In vending machines.
	Coin operated games machines.
	Washing machines.
	In cars to allow low voltage switches to operate high voltage devices such as windscreen  wipers etc.

To interface low voltage circuits with large motors, bulbs etc.

	The resistance of the operating coil.
	The number of poles and throws (see switches)
	Because they are mechanical devices they will wear out in time.
	Relays come in many shapes and sizes, choose the smallest relay which will operate  effectively in your circuit.

Name	Symbol	Picture
Solenoid

A Solenoid consists of a coil wound around a tube in which a steel plunger can move in and  out

	Solenoids convert electrical energy into linear mechanical energy.
	When current passes through the coil it becomes magnetic and pulls the plunger down into  the tube.

	To operate valves on washing machines.
	Pneumatic circuits that have to be operated electonically.
	Electronic locks.

We use them to produce small mechanical movements, for example to open and close the  jaws of a simple robot arm.

	The plunger movement is limited to a few millimeters.
	They are capable of high pulling or pushing forces.

 

  Motors

Name	Symbol	Picture
Stepper Motor
DC Motor

 

What they are

Electric motors take many different forms. The most common used in schools are small  direct current (DC) brush motors

Electric motors convert electrical energy into rotary mechanical energy.

	In toys.
	Cordless electrical appliances.
	Motor car equipment
	Cassette recorders.

Self propelled models

Powering mechanisms etc.

	Motors draw large currents and quickly exhaust batteries.
	Motors run most effectively at high speed and usually use gearboxes to slow down the  output speed.
	They are difficult to control accurately.

 

  555 Timers

Name	Symbol	Picture
555 Timer IC

 

What they are

555 Timers are integrated circuits normally contained in an eight pin dil (dual in line) package.

	555 Timers can be used to provide accurate time delays .
	They can also be used to produce regular pulses.

In many circuits associated with timing events.

Electronically controlled toasters etc.

	To produce pulse generators for counting.
	To produce a time delay.

Be careful not to bend the legs. They are easily damaged.

 

  Switches

Name	Symbol	Picture
Push Switch
Slide Switch
Toggle Switch
Rocker switch
Key Switch
Tilt Switch
Reed Switch
Micro Switch
Rotary switch
Dil switch

What they are

Mechanical switches are hand operated components that control current flow in a circuit.

What they Do

They are used to turn things on or off or divert current

Where they can be found

In almost all electrical appliances and electronic products

Why we use the

	To switch our circuits on or off.
	To control the direction of motors by reversing the current flow.

Things to watch out for...