Temporary and trial circuits are often built on breadboard which
does not require soldering.
Wires and connections
Function of Component
To pass current very easily from one part of a circuit to another.
A 'blob' should be drawn where wires are connected (joined), but it is sometimes omitted.
Wires connected at 'crossroads' should be staggered slightly to form two T-junctions,
as shown on the right.
Wires not joined
In complex diagrams it is often necessary to draw wires crossing even though they are not
connected. The simple crossing on the left is correct but may be misread as a join where
the 'blob' has been forgotten. The bridge symbol on the right leaves no doubt!
Function of Component
Supplies electrical energy. The larger terminal (on the left) is positive (+).
A single cell is often called a battery, but strictly a battery
is two or more cells joined together.
Supplies electrical energy. A battery is more than one cell. The larger terminal (on the left) is positive (+).
Converts light to electrical energy. The larger terminal (on the left) is positive (+).
Supplies electrical energy. DC = Direct Current, always flowing in one direction.
Supplies electrical energy. AC = Alternating Current, continually changing direction.
A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.
Two coils of wire linked by an iron core. Transformers are used to step up
(increase) and step down (decrease) AC voltages. Energy is transferred between
the coils by the magnetic field in the core. There is no electrical
connection between the coils.
A connection to earth. For many electronic circuits this is the 0V (zero volts)
of the power supply, but for mains electricity and some radio circuits it really
means the earth. It is also known as ground.
A coil of wire which creates a magnetic field when current passes through it.
It may have an iron core inside the coil. It can be used as a transducer
converting electrical energy to mechanical energy by pulling on something.
SPDT = Single Pole, Double Throw.
A 2-way changeover switch directs the flow of current to one of two routes according to its position.
Some SPDT switches have a central off position and are described as 'on-off-on'.
A resistor restricts the flow of current,
for example to limit the current passing through an LED.
A resistor is used with a capacitor in a timing circuit.
Some publications use the old resistor symbol:
This type of variable resistor with 2 contacts (a rheostat) is usually used to control current.
Examples include: adjusting lamp brightness, adjusting motor speed, and
adjusting the rate of flow of charge into a capacitor in a timing circuit.
This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage.
It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal.
This type of variable resistor (a preset) is operated with a small screwdriver or similar tool.
It is designed to be set when the circuit is made and then left without further adjustment.
Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.
A capacitor stores electric charge. This type must be connected the correct way round.
A capacitor is used with a resistor in a timing circuit.
It can also be used as a filter, to block DC signals but pass AC signals.
A transducer which converts temperature (heat) to resistance (an electrical property).
Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off).
For more information please see the Logic Gates page.
There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).
A NOT gate can only have one input. The 'o' on the output means 'not'. The output of a NOT gate is the inverse
(opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter.
An EX-NOR gate can only have two inputs. The 'o' on the output means 'not' showing that it is a Not
EX-OR gate. The output of an EX-NOR gate is true when its inputs are the same (both true or both false).
Sets of circuit symbols to download
You can download complete sets of all the circuit symbols shown above.
The sets are 'zipped' for convenience and they are provided in three formats:
WMF circuit symbols (32K) - Windows Metafiles.
These vector drawings are the best format for printed documents on most
computer systems, including Windows where they can be used in Word documents for example.
They can be enlarged without loss of quality.
If you are not sure which format is best for you I suggest you try this one first.
GIF circuit symbols (43K) - Graphics Interchange Format.
These bitmap images are the best format for web pages but they print poorly and
their bitmap nature will become obvious if they are enlarged. You can download individual
symbols by saving the images used above on this page.
Drawfile circuit symbols (29K) -
for RISC OS (Acorn) computers.
These high quality vector drawings are suitable for almost all documents on a
RISC OS computer. All the symbols were originally drawn in this format.
They print perfectly and can be enlarged without loss of quality.
Sorry, this format is NOT suitable for Windows computers.
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