Circuit Symbols Flashcards
Can you name this circuit symbol and describe its function?
Wire
To pass current very easily from one part of a circuit to another.
Wires joined
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!
Transformer
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.
Cell
Supplies electrical energy.
The larger terminal (on the left) is positive (+).
<small>A single cell is often called a battery, but strictly a battery is two or more cells joined together.</small>
Battery
Supplies electrical energy. A battery is more than one cell.
The larger terminal (on the left) is positive (+).
Solar Cell
Converts light to electrical energy.
The larger terminal (on the left) is positive (+).
DC supply
Supplies electrical energy.
DC = Direct Current, always flowing in one direction.
AC supply
Supplies electrical energy.
AC = Alternating Current, continually changing direction.
Fuse
A safety device which will ‘blow’ (melt) if the current flowing through it exceeds a specified value.
Earth
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.
(Ground)
Lamp (lighting)
A transducer which converts electrical energy to light. This symbol is used for a lamp providing illumination, for example a car headlamp or torch bulb.
Lamp (indicator)
A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator, for example a warning light on a car dashboard.
Heater
A transducer which converts electrical energy to heat.
Motor
A transducer which converts electrical energy to kinetic energy (rotational motion).
Bell
A transducer which converts electrical energy to sound.
Buzzer
A transducer which converts electrical energy to sound.
Inductor (Coil, Solenoid)
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.
Push Switch (push-to-make)
A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell.
Push-to-Break Switch
This type of push switch is normally closed (on), it is open (off) only when the button is pressed.
On-Off Switch
SPST = Single Pole, Single Throw.
An on-off switch allows current to flow only when it is in the closed (on) position.
2-Way Switch (SPDT)
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’.
Dual On-Off Switch (DPDT)
DPST = Double Pole, Single Throw.
A dual on-off switch which is often used to switch mains electricity because it can isolate both the live and neutral connections.
Reversing Switch (DPDT)
DPDT = Double Pole, Double Throw.
This switch can be wired up as a reversing switch for a motor. Some DPDT switches have a central off position.
