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Distinct symbols have been used to depict the different types of electronic components in circuits, since the very beginning of electrical and electronic science.
Today, circuit symbols and their usage has been pretty much standardised. This enables anyone to read a circuit diagram and know what it does relatively quickly. Schematic symbols are used to represent different electronic components and devices in circuit diagrams from wires to batteries and passive components to semiconductors, logic circuits and highly complicated integrated circuits.
By using a common set of circuit symbols in schematics, it is possible for electronic engineers around the globe to communicate circuit information concisely and without ambiguity.
It does not take too long to learn what the different circuit symbols mean. Often this comes along when learning about general electronics anyway. The symbols for more complicated integrated circuits and the like tend to be boxes with their type number included, and this means that there is not an infinite variety of different symbols to be learned and understood.
Although there are a number of different standards in use for the different circuit symbols around the globe, the differences are normally small, and because most systems are well known, there is normally little room for ambiguity.
Circuit symbol systems
There various different systems used for schematic symbols around the globe. Although there are some differences between them, the different standards bodies realise the need for common symbols and most are the same. The main circuit symbols systems and standards bodies are:
- IEC 60617: This standard is issued by the International Electrotechnical Commission, and this standard for electronic component symbols is based on the older British Standard, BS 3939 which in turn was developed from the much older British Standard 530. Often reference is made to BS electric component standard, and the IEC standard is now the one that is used. The database includes around 1750 circuit symbols overall.
- ANSI standard Y32: This standard for electronic component symbols is the American one and is also known as IEEE Std 315. This IEEE standard for circuit symbols has various release dates.
- Australian Standard AS 1102: This is an Australian standard for electronic component symbols.
Of these the IEC and ANSI/IEEE standards for electronic symbols, i.e. schemtic symbols are those that are most widely used. Both are quite similar to each other although there are a number of differences. However as many circuit diagrams are used globally, both systems will be well known to most electronics engineers.
Circuit notation and reference designators
When developing a circuit diagram or schematic, it is necessary to identify the individual components. This is particularly important when using a parts list as the components on the circuit diagram can be cross related to the parts list or Bill of Materials. It is also essential to identify components as they are often marked on the printed circuit board and in this way the circuit and the physical component can be identified for activities such as repair, etc..
In order to identify components, what is termed a circuit reference designator is used. This circuit reference designator normally consists of one or two letters followed by a number. The letters indicate the type of component, and the number, defines which particular component of that type it is. An example may be R13, or C45, etc..
In order to standardise the way in which components are identified within schematics, the IEEE introduced a standard IEEE 200-1975 as the "Standard Reference Designations for Electrical and Electronics Parts and Equipments." This was later withdrawn and later the ASME (American Society of Mechanical Engineers), initiated the new standard ASME Y14.44-2008.
Some of the more commonly used circuit reference designators are given below:
|More commonly used Circuit Schematic Reference Designators|
|Reference Designator||Component Type|
|IC||Integrated circuit - an alternative widely used non-standard abbreviation|
|J||Connector jack (normally but not always refers to female contact)|
|SW||Switch - an alternative widely used non-standard abbreviation|
|TR||Transistor - an alternative widely used non-standard abbreviation|
|XTAL||Crystal - an alternative widely used non-standard abbreviation|
|ZD||Zener diode - an alternative widely used non-standard abbreviation|
Circuit diagram symbols
As there are very many different circuit symbols to cover the wide range of different components of all types, they have been split down and presented on different pages according to their categories
|Circuit Symbols Pages|
|Resistors||Resistor circuit symbols.|
|Capacitors||Capacitor circuit symbols.|
|Inductive compoennts||Inductive component circuit symbols.|
|Diodes||Diode circuit symbols.|
|Bipolar transistor||Bipolar transistor circuit symbols.|
|Field effect transistor, FET||FET circuit symbols.|
|Wires, switches, connectors||Wires, switches and connectors circuit symbols.|
|Analogue circuit blocks||Analogue circuit blocks circuit symbols.|
|Logic functions||Logic circuit symbols.|
By using the various standard circuit symbols in schematic diagrams, it is possible to create a diagram that is not only easy to read, but also open to less mis-interpretation than if non-standard symbols are used.