Symbols

Resistors

A variety of symbols are used to denote different types of resistor. It is worth noting the difference between preset and variable components and also that potentiometers have three, rather than two connections.

Capacitors

Conventional, non-electrolytic capacitors can be connected into a circuit either way round. Electrolytic capacitors, on the other hand, require a d.c. polarizing voltage and must be connected with the correct polarity.

Inductors

Symbols for inductors can be used to indicate the type of core when it is something other than air. Dotted lines indicate a ferrite core whilst solid lines indicate an iron (or steel) core.

Diodes etc.

Thyristors and triacs have a third terminal (the 'gate' or 'trigger') in addition to anode and cathode or 'main terminal 1' and 'main terminal 2', respectively. The bridge rectifier comprises a network of four diodes (note that the junction of the two cathodes forms the positive d.c. output terminal whilst the junction of the two anodes forms the negative d.c. output terminal).

Transistors

A large number of symbols are used to denote a variety of different transistor types. The two most common symbols are those that are associated with bipolar devices - note that the arrow points outwards at the emitter of an NPN transistor and inwards at the emitter of a PNP transistor.

Integrated Circuits

Many integrated circuits have specialized functions and no particular symbol is associated with them. Logic gates and operational amplifiers, on the other hand, do have recognizable symbols. Note that the '+' and '-' signs on the operational amplifier are used to indicate the 'non-inverting' and 'inverting' inputs respectively - not the power supply connections!

Switches

The symbols shown here include the most common types of single-pole, double-pole, and multi-pole switch. Note that a mechanical linkage is sometimes indicated by means of a dotted line linking the contacts operated by a common switch mechanism.

Indicators and Transducers

Only a small selection of symbols for indicators and transducers is shown here - a number of common types of transducer (such as the photodiode and the light dependent resistor) appear within the other main categories of component.

Miscellaneous

This collection of miscellaneous symbols includes the symbols used to depict single and multi-cell batteries as well as those used for common or ground connections.