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Symbols

Circuit diagram symbols have differed from country to country and have changed over time, but are now to a large extent internationally standardized. Simple components often had symbols intended to represent some feature of the physical construction of the device. For example, the symbol for a resistor shown here dates back to the days when that component was made from a long piece of wire wrapped in such a manner as to not produce inductance, which would have made it a coil. These wirewound resistors are now used only in high-power applications, smaller resistors being cast from carbon composition (a mixture of carbon and filler) or fabricated as an insulating tube or chip coated with a metal film. The internationally standardized symbol for a resistor is therefore now simplified to an oblong, sometimes with the value in ohms written inside, instead of the zig-zag symbol. A less common symbol is simply a series of peaks on one side of the line representing the conductor, rather than back-and-forth as shown here.
Schematic wire junctions:
1. Old style: (a) connection, (b) no connection.
2. One CAD style: (a) connection, (b) no connection.
3. Recommended CAD Style: (a) connection, (b) no connection.
The linkages between leads were once simple crossings of lines; one wire insulated from and "jumping over" another was indicated by it making a little semicircle over the other line. With the arrival of computerized drafting, a connection of two intersecting wires was shown by a crossing with a dot or "blob", and a crossover of insulated wires by a simple crossing without a dot. However, there was a danger of confusing these two representations if the dot was drawn too small or omitted. Modern practice is to avoid using the "crossover with dot" symbol, and to draw the wires meeting at two points instead of one.[2][3][4] It is also common to use a hybrid style, showing connections as a cross with a dot while insulated crossings use the semicircle.
On a circuit diagram, the symbols for components are labelled with a descriptor or reference designator matching that on the list of parts. For example, C1 is the first capacitor, L1 is the first inductor, Q1 is the first transistor, and R1 is the first resistor (note that this is not written as a subscript, as in R1, L1,…). Often the value or type designation of the component is given on the diagram beside the part, but detailed specifications would go on the parts list.
Detailed rules for reference designations are provided in the International standard IEC 61346.


COMPONENT SYMBOL ALTERNATE
Ammeter
[Schematic Symbol]
And Gate
[Schematic Symbol]
Antenna, Balanced
[Schematic Symbol]
Antenna, General
[Schematic Symbol]
[Schematic Symbol]
Antenna, Loop, Shielded
[Schematic Symbol]
Antenna, Loop, Unshielded
[Schematic Symbol]
Antenna, Unbalanced
[Schematic Symbol]
[Schematic Symbol]
Attenuator, Fixed
[Schematic Symbol]
Attenuator, Variable
[Schematic Symbol]
Battery
[Schematic Symbol]
Capacitor, Feedthrough
[Schematic Symbol]
Capacitor, Fixed, Nonpolarized
[Schematic Symbol]
Capacitor, Fixed, Polarized
[Schematic Symbol]
Capacitor, Ganged, Variable
[Schematic Symbol]
Capacitor, General
[Schematic Symbol]
Capacitor, Variable, Single
[Schematic Symbol]
Capacitor, Variable, Split-Stator
[Schematic Symbol]
Cathode, Cold
[Schematic Symbol]
Cathode, Directly Heated
[Schematic Symbol]
Cathode, Indirectly Heated
[Schematic Symbol]
[Schematic Symbol]
Cavity Resonator
[Schematic Symbol]
Cell
[Schematic Symbol]
Circuit Breaker
[Schematic Symbol]
Coaxial Cable
[Schematic Symbol]
[Schematic Symbol]
Crystal, Piezoelectric
[Schematic Symbol]
Delay Line
[Schematic Symbol]
[Schematic Symbol]
Diode, General
[Schematic Symbol]
Diode, Gunn
[Schematic Symbol]
Diode, Light-Emitting
[Schematic Symbol]
Diode, Photosensitive
[Schematic Symbol]
Diode, Photovoltaic
[Schematic Symbol]
Diode, Pin
[Schematic Symbol]
Diode, Varactor
[Schematic Symbol]
Diode, Zener
[Schematic Symbol]
Directional Coupler
[Schematic Symbol]
[Schematic Symbol]
Exclusive-Or Gate
[Schematic Symbol]
Female Contact, General
[Schematic Symbol]
Ferrite Bead
[Schematic Symbol]
[Schematic Symbol]
Fuse
[Schematic Symbol]
[Schematic Symbol]
Galvanometer
[Schematic Symbol]
[Schematic Symbol]
Ground, Chassis
[Schematic Symbol]
[Schematic Symbol]
Ground, Earth
[Schematic Symbol]
Handset
[Schematic Symbol]
Headphone, Double
[Schematic Symbol]
Headphone, Single
[Schematic Symbol]
Inductor, Air-Core
[Schematic Symbol]
Inductor, Bifilar
[Schematic Symbol]
Inductor, Iron-Core
[Schematic Symbol]
Inductor, Tapped
[Schematic Symbol]
Inductor, Variable
[Schematic Symbol]
[Schematic Symbol]
Integrated Circuit
[Schematic Symbol]
Inverter
[Schematic Symbol]
Jack, Coaxial
[Schematic Symbol]
Jack, Phone, 2-Conductor
[Schematic Symbol]
Jack, Phone, 2-Conductor Interrupting
[Schematic Symbol]
Jack, Phone, 3-Conductor
[Schematic Symbol]
Jack, Phono
[Schematic Symbol]
Key, Telegraph
[Schematic Symbol]
Lamp, Incandescent
[Schematic Symbol]
Lamp, Neon
[Schematic Symbol]
Male Contact, General
[Schematic Symbol]
Microphone
[Schematic Symbol]
Nand Gate
[Schematic Symbol]
Negative Voltage Connection
[Schematic Symbol]
Nor Gate
[Schematic Symbol]
Operational Amplifier
[Schematic Symbol]
Or Gate
[Schematic Symbol]
Outlet, Utility, 117-V
[Schematic Symbol]
Outlet, Utility, 234-V
[Schematic Symbol]
Photocell, Tube
[Schematic Symbol]
Plug, Phone, 2-Conductor
[Schematic Symbol]
Plug, Phone, 3-Conductor
[Schematic Symbol]
Plug, Phono
[Schematic Symbol]
Plug, Utility, 117-V
[Schematic Symbol]
Plug, Utility, 234-V
[Schematic Symbol]
Positive Voltage Connection
[Schematic Symbol]
Potentiometer
[Schematic Symbol]
[Schematic Symbol]
Probe, Radio-Frequency
[Schematic Symbol]
Rectifier, Semiconductor
[Schematic Symbol]
Rectifier, Silicon-Controlled
[Schematic Symbol]
Rectifier, Tube-Type
[Schematic Symbol]
Relay, DPDT
[Schematic Symbol]
Relay, DPST
[Schematic Symbol]
Relay, SPDT
[Schematic Symbol]
Relay, SPST
[Schematic Symbol]
Resistor
[Schematic Symbol]
Resonator
[Schematic Symbol]
Rheostat
[Schematic Symbol]
[Schematic Symbol]
Saturable Reactor
[Schematic Symbol]
Shielding
[Schematic Symbol]
Signal Generator
[Schematic Symbol]
Speaker
[Schematic Symbol]
[Schematic Symbol]
Switch, DPDT
[Schematic Symbol]
Switch, DPST
[Schematic Symbol]
Switch, Momentary-Contact
[Schematic Symbol]
Switch, Rotary
[Schematic Symbol]
Switch, SPDT
[Schematic Symbol]
Switch, SPST
[Schematic Symbol]
Terminals, General, Balanced
[Schematic Symbol]
Terminals, General, Unbalanced
[Schematic Symbol]
Test Point
[Schematic Symbol]
Thermocouple
[Schematic Symbol]
[Schematic Symbol]
Thyristor
[Schematic Symbol]
Transformer, Air-Core
[Schematic Symbol]
Transformer, Iron-Core
[Schematic Symbol]
Transformer, Tapped Primary
[Schematic Symbol]
Transformer, Tapped Secondary
[Schematic Symbol]
Transistor, Bipolar, npn
[Schematic Symbol]
Transistor, Bipolar, pnp
[Schematic Symbol]
Transistor, Field-Effect, N-Channel
[Schematic Symbol]
Transistor, Field-Effect, P-Channel
[Schematic Symbol]
Transistor, Metal-Oxide, Dual-Gate
[Schematic Symbol]
Transistor, Metal-Oxide, Single-Gate
[Schematic Symbol]
Transistor, Photosensitive
[Schematic Symbol]
Transistor, Unijunction
[Schematic Symbol]
Tube, Diode
[Schematic Symbol]
Tube, Pentode
[Schematic Symbol]
Tube, Photomultiplier
[Schematic Symbol]
Tube, Tetrode
[Schematic Symbol]
Tube, Triode
[Schematic Symbol]
Unspecified Component
[Schematic Symbol]
Voltmeter
[Schematic Symbol]
Wattmeter
[Schematic Symbol]
[Schematic Symbol]
Wires
[Schematic Symbol]
Wires, Connected, Crossing
[Schematic Symbol]
[Schematic Symbol]
Wires, Not Connected, Crossing
[Schematic Symbol]
[Schematic Symbol]

Artwork onto a printed circuit board (PCB
Once the schematic has been made, it is converted into a layout that can be fabricated onto a printed circuit board (PCB). The layout is usually started by the process of schematic capture. The result is what is known as a rat's nest. The rat's nest is a jumble of wires (lines) criss-crossing each other to their destination nodes. These wires are routed either manually or by the use of electronics design automation (EDA) tools. The EDA tools arrange and rearrange the placement of components and find paths for tracks to connect various nodes. This results in the final layout artwork for the integrated circuit or printed circuit board.[5]
A generalized design flow would be as:
Schematic → Schematic capture → Rat's nest → Routing → Artwork → PCB development & etching → Component mounting → Testing

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