Electronic 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 stripboard or printed circuit board.

Wires and connections

Component Circuit Symbol Function of Component
Wire wire symbol To pass current very easily from one part of a circuit to another.
Wires joined wires joined symbol 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 wires crossing but not joined symbol In complex diagrams it is often necessary to draw wires crossing even though they are not connected. I prefer the 'hump' symbol shown on the right because the simple crossing on the left may be misread as a join where you have forgotten to add a 'blob'!

Power Supplies

Component Circuit Symbol Function of Component
Cell cell symbol Supplies electrical energy. A single cell is often wrongly called a battery, but strictly a battery is two or more cells joined together.
Battery battery symbol Supplies electrical energy. A battery is more than one cell.
DC supply DC power supply symbol Supplies electrical energy.
DC = Direct Current, always flowing in one direction.
AC supply AC power supply symbol Supplies electrical energy.
AC = Alternating Current, continually changing direction.
Fuse fuse symbol A safety device which will 'blow' (melt) if the current flowing through it exceeds a specified value.
Transformer transformer symbol 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)		 earth symbol 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) lamp (lighting) symbol 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) lamp (indicator) symbol 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 heater symbol A transducer which converts electrical energy to heat.
Motor motor symbol A transducer which converts electrical energy to kinetic energy (motion).
Bell bell symbol A transducer which converts electrical energy to sound.
Buzzer buzzer symbol A transducer which converts electrical energy to sound.
Inductor
(Coil, Solenoid)		 inductor symbol 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)		 push-to-make switch symbol 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 push-to-break switch symbol This type of push switch is normally closed (on), it is open (off) only when the button is pressed.
On-Off Switch
(SPST)		 SPST on-off switch symbol 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 switch symbol 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 switch symbol 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 switch symbol 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 relay symbol 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.

Resistors

Component Circuit Symbol Function of Component
Resistor resistor symbol 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)		 rheostat 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.
Variable Resistor
(Potentiometer)		 potentiometer symbol 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.
Variable Resistor
(Preset)		 preset symbol 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.

Capacitors

Component Circuit Symbol Function of Component
Capacitor capacitor symbol 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, polarised polarised capacitor symbol 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 variable capacitor symbol A variable capacitor is used in a radio tuner.
Trimmer Capacitor trimmer capacitor symbol This type of variable capacitor (a trimmer) 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.

Diodes

Component Circuit Symbol Function of Component
Diode diode symbol A device which only allows current to flow in one direction.
LED
Light Emitting Diode		 LED symbol A transducer which converts electrical energy to light.
Zener Diode zener diode symbol A special diode which is used to maintain a fixed voltage across its terminals.
Photodiode photodiode symbol A light-sensitive diode.

Transistors

Component Circuit Symbol Function of Component
Transistor NPN NPN transistor symbol A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.
Transistor PNP PNP transistor symbol A transistor amplifies current. It can be used with other components to make an amplifier or switching circuit.
Phototransistor Phototransistor symbol A light-sensitive transistor.

Audio and Radio Devices

Component Circuit Symbol Function of Component
Microphone microphone symbol A transducer which converts sound to electrical energy.
Earphone earphone symbol A transducer which converts electrical energy to sound.
Loudspeaker loudspeaker symbol A transducer which converts electrical energy to sound.
Piezo Transducer piezo transducer symbol A transducer which converts electrical energy to sound.
Amplifier
(general symbol)		 amplifier 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)		 aerial symbol 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 voltmeter symbol A voltmeter is used to measure voltage.
The proper name for voltage is 'potential difference', but most people prefer to say voltage!
Ammeter ammeter symbol An ammeter is used to measure current.
Galvanometer galvanometer symbol A galvanometer is a very sensitive meter which is used to measure tiny currents, usually 1mA or less.
Ohmmeter ohmmeter symbol An ohmmeter is used to measure resistance. Most multimeters have an ohmmeter setting.
Oscilloscope oscilloscope symbol An oscilloscope is used to display the shape of electrical signals and it can be used to measure their voltage and time period.

Sensors (input devices)

Component Circuit Symbol Function of Component
LDR LDR symbol A transducer which converts brightness (light) to resistance (an electrical property).
LDR = Light Dependent Resistor
Thermistor thermistor symbol A transducer which converts temperature (heat) to resistance (an electrical property).

Logic Gates

Gate Type Traditional Symbol IEC Symbol Function of Gate
NOT NOT gate traditional symbol NOT gate IEC symbol 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 AND gate traditional symbol AND gate IEC symbol An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true.
NAND NAND gate traditional symbol NAND gate IEC symbol 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 OR gate traditional symbol OR gate IEC symbol 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 NOR gate traditional symbol NOR gate IEC symbol 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 EX-OR gate traditional symbol EX-OR gate IEC symbol 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 EX-NOR gate traditional symbol EX-NOR gate IEC symbol 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).