Download Circuit Symbol T1 PDF

TitleCircuit Symbol T1
Tags Electric Current Inductor Capacitor Electronic Component
File Size228.1 KB
Total Pages8
Table of Contents
                            Circuit Symbols
	Wires and connections
	Power Supplies
	Output Devices: Lamps, Heater, Motor, etc.
	Switches
	Resistors
	Capacitors
	Diodes
	Transistors
	Audio and Radio Devices
	Meters and Oscilloscope
	Sensors (input devices)
	Logic Gates
                        
Document Text Contents
Page 1

Circuit Symbols

Circuit symbols are used in circuit diagrams, which show how a circuit is connected
together. The actual layout of the components is usually quite different from the circuit
diagram. To build a circuit you need a different diagram showing the layout of the parts
on the printed circuit board. However understanding electronics circuit give you a better
understanding of how to find faults in an electronic circuit

Wires and connections

Component Circuit Symbol Function of Component

Wire
To conduct or pass current 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 to another wire
should be staggered slightly to form two T-
junctions, as shown. Such help to
transmitted current to other paths

Wires not joined



In diagrams it is often necessary to draw
wires crossing even though they are not
connected. It is preferred to have the 'hump'
symbol as shown because the simple
crossing of the wire may be misread as a
join where you have forgotten to add a
'blob'!

Power Supplies

Component Circuit Symbol Function of Component

Cell



Supplies electrical energy.
The larger terminal indicates the positive (+).
A single cell is often interpreted and called a
battery, but a battery is two or more cell
joined together.

Battery



Supplies electrical energy. A battery is more
than one cell.
The larger terminal is the positive (+). And

Page 2

the small terminal is called the negative (-)

DC supply + -
Supplies electrical energy.
DC = Direct Current, always flowing in one
direction.

AC supply

Supplies electrical energy.
AC = Alternating Current, continually
changing direction of it currents it is negative
and then Positive which alternates again.

Fuse

A safety device, which will 'blow' or melt if the
current flowing through it exceeds a specified
value. Used as a protection for electrical
circuits.

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.

Earth
(Ground)

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.

Output Devices: Lamps, Heater, Motor, etc.

Component Circuit Symbol Function of Component

Lamp (lighting)


A transducer, which converts electrical
energy to light. This symbol is used for a
lamp providing illumination, for example a car
headlamp.

Motor


A transducer, which converts electrical
energy to kinetic energy (motion).

Bell



A transducer, which converts electrical
energy to sound.

Buzzer



A transducer, which converts electrical
energy to sound.

Page 3

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.

Switches

Component Circuit Symbol Function of Component

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. It is a
abbreviated NO for normally open .

Push-to-Break
Switch



This type of push switch is normally
closed abbreviated NC for normally
closed (on), it is open (off) only when the
button is pressed.

On-Off Switch
(SPST)

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
(DPST)

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.

Relay



An electrically operated switch, for
example a 9V battery circuit connected to
the coil can switch a 230V AC mains
circuit.
NO = Normally Open, COM = Common,
NC = Normally Closed.

Page 4

Resistors

Component Circuit Symbol Function of Component

Resistor

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.

Variable Resistor
(Rheostat)



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.

Variable Resistor
(Potentiometer)



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.

Capacitors

Component Circuit Symbol Function of Component

Capacitor



A capacitor stores electric charge. 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.

Capacitor,
polarized



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.

Variable Capacitor



A variable capacitor is used in a radio
tuner.

Page 5

Diodes

Component Circuit Symbol Function of Component

Diode


A device, which only allows current to flow
in one direction.

LED
Light Emitting Diode



A transducer, which converts electrical
energy to light.

Zener Diode


A special diode, which is used to maintain a
fixed voltage in a power supply.

Photodiode


A light-sensitive diode. Which react when
light is shine direct on it may increase or
decrease it resistance

Transistors

Component Circuit Symbol Function of Component

Transistor NPN



A transistor amplifies current. It can be used with
other components to make an amplifier or switching
circuit.

Transistor PNP



A transistor amplifies current. It can be used with
other components to make an amplifier or switching
circuit.

Phototransistor



A light-sensitive transistor.

Audio and Radio Devices

Component Circuit Symbol Function of Component

Microphone


A transducer, which converts sound to electrical
energy.

Page 6

Earphone



A transducer, which converts electrical energy to
sound.

Loudspeaker



A transducer, which converts electrical energy to
sound.

Piezo Transducer



A transducer, which converts electrical energy to
sound.

Amplifier
(general symbol)



An amplifier circuit with one input. Really it is a
block diagram symbol because it represents a
circuit rather than just one component.

Aerial
(Antenna)



A device, which is designed to receive or
transmit radio signals. It is also known as an
antenna.

Meters and Oscilloscope

Component Circuit Symbol Function of Component

Voltmeter


A voltmeter is used to measure voltage.
The proper name for voltage is 'potential difference',
but most people prefer to say voltage!

Amp-meter


An amp-meter is used to measure current.
As known as amps

Ohmmeter


An ohmmeter is used to measure resistance.
Most Multimeter have an ohmmeter setting.

Sensors (input devices)

Component Circuit Symbol Function of Component

Thermistor


A transducer which converts temperature
(heat) to resistance (an electrical property).

Page 7

Logic Gates
Logic gates process signals, which represent true (1, high, +Vs, on) or false (0, low, 0V,
off).

Gate
Type

Traditional
Symbol

IEC Symbol Function of Gate

NOT



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.

AND



An AND gate can have two or more
inputs. The output of an AND gate is
true when all its inputs are true.

NAND



A NAND gate can have two or more
inputs. The 'o' on the output means 'not'
showing that it is a Not AND gate. The
output of a NAND gate is true unless all
its inputs are true.

OR



An OR gate can have two or more
inputs. The output of an OR gate is true
when at least one of its inputs is true.

NOR



A NOR gate can have two or more
inputs. The 'o' on the output means 'not'
showing that it is a Not OR gate. The
output of a NOR gate is true when none
of its inputs are true.

EX-OR



An EX-OR gate can only have two
inputs. The output of an EX-OR gate is
true when its inputs are different (one
true, one false).

EX-
NOR



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

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