Electronic Component Symbols

Wires joined

A 'blob' should be drawn where wires are connected (joined), but it is sometimes is left out. Wires connected to another wire should touch slightly to form two T-junctions, as shown. Such help totransmitted current to other paths

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

Aerial

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

Diode

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

Photodiode

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

Phototransistor

A light-sensitive transistor

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

Zener Diode

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

Capacitor

A 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 stores electric charge. This type must be connected the correct way round. It is used with a resistor in a timingcircuit. It can also be used as a filter, to block DC signals but pass ACsignals

LDR

A transducer which converts brightness (light) to resistance (an electrical property). Stands for Light Dependent Resistor

Heater

A transducer which converts electrical energy to heat

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

Thermistor

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

Motor

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

LED Light Emitting Diode

A transducer, which converts electrical energy to light.

Lamp (lighting)

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

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

Microphone

A transducer, which converts sound to electrical energy.

Transistor PNP

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

Transistor NPN

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

Galvanometer

A very sensitive meter which is used to measure tiny currents, usually 1mA or less

Push switch

Allows current to flow only when the button is pressed. This is the switch used to operate a doorbell. It is an abbreviated NO for normally open

Amplifier (general symbol)

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

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.

OR

Can have two or more inputs. The output is true when at least one of its inputs is true

Dual On-Off Switch

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

Reversing Switch

DPDT = Double Pole, Double Throw.This switch can be wired up as a reversing switch for a motor. SomeDPDT switches have a central off position

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'

MAND

It 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

NOR

It can have two or more inputs. The 'o' on the output means 'not' showing that it is a Not OR gate. The output of it is true when none of its inputs are true.

AND

It can have two or more inputs. The output of it is true when all its inputs are true.

NOT

It can only have one input. The 'o' on the output means'not'. The output of its gate is the inverse (opposite) of its input, so the output is true when the input is false. Also called an inverter.

EX-OR

It can only have two inputs. Its output is true when its inputs are different (one true, one false)

EX-NOR

It can only have two inputs. The 'o' on the output means 'not' showing that it is a Not EX-OR gate. The output of anEX-NOR gate is true when its inputs are the same (both true or both false)

Resistor

Restricts the flow of current, for example, to limit the current passing through an LED. Used with a capacitor in a timing circuit

2-way switch

SPDT = Single Pole, Double Throw. It 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

On-Off Switch

SPST = Single Pole, Single Throw. Allows current to flow only when it is in the closed(on) position

Cell

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

Battery

Supplies electrical energy. It is more than one cell.The larger end is the positive (+). And the small end is called the negative (-)

DC supply

Supplies electrical energy. Stand for Direct Current, always flowing in one direction.

AC supply

Supplies electrical energy. Stands for Alternating Current, continually changing the direction of its currents, it is negative and then Positive which alternates again.

Variable Resistor (Rheostat)

This is used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into acapacitor in a timing circuit

Variable Resistor (Preset)

This 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

Push-to-Break Switch

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

Trimmer Capacitor

This type of variable capacitor 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

Wire

To conduct/guide or pass current from one part of a circuit to another

Transformer

Two coils of wire linked by an iron core. They 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

Variable Capacitor

Used in a radio tuner

Oscilloscope

Used to display the shape of electrical signals and it canbe used to measure their voltage and time period

Amp-meter

Used to measure current. As known as amps

Ohmmeter

Used to measure resistance. Most Multimeter have an ohmmeter setting

Voltmeter

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