# Electronic symbol

An electronic symbol is a pictogram used to represent various electrical and electronic devices or functions, such as wires, batteries, resistors, and transistors, in a schematic diagram of an electrical or electronic circuit. These symbols are largely standardized internationally today, but may vary from country to country, or engineering discipline, based on traditional conventions.

## Standards for symbols

The graphic symbols used for electrical components in circuit diagrams are covered by national and international standards, in particular:
* IEC 60617 (also known as BS 3939).
* There is also IEC 61131-3 – for ladder-logic symbols.
* JIC JIC (Joint Industrial Council) symbols as approved and adopted by the NMTBA (National Machine Tool Builders Association). They have been extracted from the Appendix of the NMTBA Specification EGPl-1967.
* ANSI Y32.2-1975 (also known as IEEE Std 315-1975 or CSA Z99-1975).
* IEEE Std 91/91a: graphic symbols for logic functions (used in digital electronics). It is referenced in ANSI Y32.2/IEEE Std 315.
* Australian Standard AS 1102 (based on a slightly modified version of IEC 60617; withdrawn without replacement with a recommendation to use IEC 60617).
The standards do not all agree, and use of unusual (even if standardized) symbols can lead to confusion and errors. Symbols usage is sometimes idiosyncratic to engineering disciplines, and national or local variations to international standards exist. For example, lighting and power symbols used as part of architectural drawings may be different from symbols for devices used in electronics.

## Common electronic symbols

Symbols shown are typical examples, not a complete list.

### Grounds

The shorthand for ground is GND. Optionally, the triangle in the middle symbol may be filled in.
* General ground (IEC‑style)
* Signal/low-noise ground (the asterisk is not part of the symbol)
* Chassis/Earth ground (IEC‑style)

### Sources

* Battery, single-cell
* Battery, multi-cell
* Solar (photovoltaic) cell
* DC voltage source
* Controlled DC voltage source
* Current source
* Controlled current source
* AC voltage source

### Resistors

It is very common for potentiometer and rheostat symbols to be used for many types of variable resistors and trimmers.
* ANSI‑style: (a) Resistor, (b) Rheostat, (c) Potentiometer / Trimmer
* IEC‑style: (a) Resistor, (b) Rheostat, (c) Potentiometer / Trimmer
* Photoresistor (ANSI)
* Thermistor (ANSI).Use -t for NTC symbol.Use +t for PTC symbol.
* Varistor (ANSI)

### Capacitors

* General capacitor (IEC‑style); sometimes drawn with one plate curved
* Polarized capacitor (American‑style), such as electrolytic and tantalum capacitors
* Variable capacitor
* Ganged (co‑moving) variable capacitors (IEC‑style)
* Trimmer variable capacitor

### Diodes

Optionally, the triangle in these symbols may be filled in, or a line may be drawn through the triangle (less desirable). The words anode and cathode aren't part of the diode symbols. For instructional purposes, sometimes two letters (A/C or A/K) are placed next to diode symbols similar to how the letters C/B/E or D/G/S are placed next to transistor symbols. "K" is often used instead of "C", because the origin of the word cathode is kathodos, and to avoid confusion with "C" for capacitors in silkscreen of printed circuit boards.
* Diode (rectifier)
* Schottky diode
* Zener diode
* TVS (Transient Voltage Suppression) diode. Top is unidirectional, bottom is bidirectional.
* LED (Light Emitting Diode)
* Photodiode
* Tunnel diode
* Varicap
* Shockley diode
* SCR (Silicon Controlled Rectifier)
* Diac (may be a varistor in older schematics)
* Constant-current diode
* Opto-isolator: internal LED (left) and photo transistor (right)

#### Bridge rectifiers

There are many ways to draw a single-phase bridge rectifier symbol. Some simplified symbols don't show the internal diodes.
* Bridge rectifier
* Bridge rectifier
* Bridge rectifier
* Bridge rectifier
* Three-phase bridge rectifier

### Inductors

An inductor can be drawn either as a series of loops, or series of half-circles.
* Inductor symbol (series of loops)
* Air-core inductor (IEC‑style)
* Magnetic-core inductor (IEEE‑style)
* Tapped inductor (IEC‑style)
* Ferrite bead (IEEE‑style)
* Variable inductor
* Trimmer variable inductor

### Transformers

* Transformer
* Transformer with center tap on secondary winding (right side)
* Transformer with two secondary windings (right side)
* Current transformer
* Zero-sequence current transformer (ZSCT) (also known as a window-type current transformer)
* Bushing-type current transformer
* Voltage transformer

### Transistors

Optionally, transistor symbols may include a circle. Note: The pin letters B/C/E and G/D/S aren't part of the transistor symbols.

#### Bipolar

* NPN bipolar junction transistor (BJT)
* PNP bipolar junction transistor (BJT)
* NPN Darlington transistor
* PNP Darlington transistor
* NPN Phototransistor

#### Unipolar

* N-channel junction gate field-effect transistor (JFET)
* P-channel junction gate field-effect transistor (JFET)
* Metal–oxide–semiconductor field-effect transistor (MOSFET)
* Enhancement mode, N‑channel MOSFET
* Enhancement mode, P‑channel MOSFET

### Vacuum tubes

* Vacuum tube diode
* Vacuum tube triode
* Vacuum tube tetrode (pin letters not part of symbol)
* Vacuum tube pentode

### Switches

For multiple pole switches, a dotted or dashed line can be included to indicate two or more switch at the same time (see DPST and DPDT examples below).
* Pushbutton, normally open, push-to-make (horizontal line on top)
* Pushbutton, normally open, push-to-make (IEEE-style)
* Pushbutton, normally closed, push-to-break (IEEE-style)
* Pushbutton, normally closed, two circuits (IEEE-style)
* Switch, 1P1T, SPST (single-pole single-throw)
* Switch, 2P1T, DPST (double-pole single-throw)
* Switch, 1P2T, SPDT (single-pole double-throw)
* Switch, 2P2T, DPDT (double-pole double-throw)
* Rotary switch, 1P3T, break-before-make, nonshorting style
* Rotary switch, 1P4T, break-before-make, nonshorting style
* Rotary switch, 1P4T, make-before-break, shorting style
* Slide switch, 1P4T, make-before-break, shorting style
* Reed switch, normally open

### Relays

Relays symbols are a combination of an inductor symbol and switch symbol.
Note: The pin letters in these symbols aren't part of the standard relay symbol.
* SPST, SPDT, DPST, DPDT relays (American‑style)
* SPDT relay (IEC‑style)

### Lamps

LED is located in the diode section.
* Neon lamp
* Indicating lamp (IEEE‑style)
* Incandescent lamp
* Indicatory incandescent light bulb
* Light bulb

### Current limiters

* IEC fuse (b), equivalent symbols (a, c) (IEEE Std 315-1975)
* Molded-case circuit breaker (MCCB)
* Fuse: IEC (top) and American (lower two)

### Voltage limiters

TVS and Zener diodes are located in the diode section.
* Gas-discharge tubes (GDT) for ESD discharge
* Spark gap for ESD discharge

### Electro-acoustic devices

Speaker symbols sometimes include an internal inductor symbol.
* Loudspeaker (IEEE-style)
* Buzzer (IEC-style)
* Microphone (IEEE-style)
* Microphone (IEC-style)

### Antennas

* General antenna (IEC-style)
* Dipole antenna (IEC-style)
* Loop antenna (IEC-style)
* Loop antenna (IEEE-style)

### Cables

* Cable, Shielded 1 conductor
* Cable, 2 conductor
* Cable, Shielded 2 conductor with shield connected to ground
* Cable, 5 conductor
* Cable, Shielded 5 conductor

### Connectors

There are numerous connector symbol variations.
* Phone connectors. "A" is TS, "B" is TRS, "D" is TRS with two switches.
* 5x2 shrouded header with notch key and pin names for Olimex UEXT.
* DE-9 D-subminiature with host side pin names for RS-232 serial port.

### ICs
#### Logic gates

For the symbols below: A and B are inputs, Q is output. Note: These letters are not part of the symbols.
There are variations of these logic gate symbols. Depending on the IC, the two-input gates below may have: 1) two or more inputs; 2) infrequently some have a second inverted Q output too.
* Buffer
* Inverter (NOT)
* AND
* NAND
* OR
* NOR
* XOR
* XNOR
The above logic symbols may have additional I/O variations too: 1) schmitt trigger inputs, 2) tri-state outputs, 3) open-collector or open-drain outputs (not shown).
* Buffer gate with schmitt trigger input
* Buffer gate with tri-state output control. (B is the tri-state control)

#### Flip-flops

For the symbols below: Q is output, Q is inverted output, E is enable input, internal triangle shape is clock input, S is Set, R is Reset (some datasheets use clear (CLR) instead of reset along the bottom).
There are variations of these flip-flop symbols. Depending on the IC, a flip-flop may have: 1) one or both outputs (Q only, Q only, both Q & Q); 2) one or both forced inputs along top & bottom (R only, S only, both R & S); 3) some inputs may be inverted.
* Simple SR flip-flop (inverted S & R inputs)
* Gated SR flip-flop
* Gated D flip-flop (Transparent Latch)
* Clocked D flip-flop (Set & Reset inputs)
* Clocked JK flip-flop
* Clocked T flip-flop

#### OpAmps

Note: The outside text isn't part of these symbols.
* Operational amplifier (opamp)
* Comparator

### Oscillators

* Crystal oscillator (IEEE‑style)
* Ceramic resonator (3 pins)

### Miscellaneous devices

* Hall-effect sensor

## Historical electronic symbols

The shape of some electronic symbols have changed over time. The following historical electronic symbols can be found in old electronic books / magazines / schematics, and now considered obsolete.

### Capacitors (historical)

All of the following are obsolete capacitor symbols.
* Obsolete capacitor (very old style)
* Obsolete capacitor
* Obsolete capacitor
* Obsolete capacitor
* Obsolete capacitor