Circuit diagram

Last updated January 21, 2024

A circuit diagram (or: wiring diagram, electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an electrical circuit. A pictorial circuit diagram uses simple images of components, while a schematic diagram shows the components and interconnections of the circuit using standardized symbolic representations. The presentation of the interconnections between circuit components in the schematic diagram does not necessarily correspond to the physical arrangements in the finished device.^[1]

Symbols

Circuit diagrams are pictures with symbols that 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 dates back to the time 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.

The linkages between leads were once simple crossings of lines. With the arrival of computerized drafting, the connection of two intersecting wires was shown by a crossing of wires with a "dot" or "blob" to indicate a connection. At the same time, the crossover was simplified to be the same crossing, but without a "dot". However, there was a danger of confusing the wires that were connected and not connected in this manner, if the dot was drawn too small or accidentally omitted (e.g. the "dot" could disappear after several passes through a copy machine).^[4] As such, the modern practice for representing a 4-way wire connection is to draw a straight wire and then to draw the other wires staggered along it with "dots" as connections (see diagram), so as to form two separate T-junctions that brook no confusion and are clearly not a crossover.^[5]^[6]

For crossing wires that are insulated from one another, a small semi-circle symbol is commonly used to show one wire "jumping over" the other wire^[3]^[7]^[8] (similar to how jumper wires are used).

A common, hybrid style of drawing combines the T-junction crossovers with "dot" connections and the wire "jump" semi-circle symbols for insulated crossings. In this manner, a "dot" that is too small to see or that has accidentally disappeared can still be clearly differentiated from a "jump".^[3]^[7]

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. 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.

Organization

It is a usual (although not universal) convention that schematic drawings are organized on the page from left to right and top to bottom in the same sequence as the flow of the main signal or power path. For example, a schematic for a radio receiver might start with the antenna input at the left of the page and end with the loudspeaker at the right. Positive power supply connections for each stage would be shown towards the top of the page, with grounds, negative supplies, or other return paths towards the bottom. Schematic drawings intended for maintenance may have the principal signal paths highlighted to assist in understanding the signal flow through the circuit. More complex devices have multi-page schematics and must rely on cross-reference symbols to show the flow of signals between the different sheets of the drawing.

Detailed rules for the preparation of circuit diagrams, and other document types used in electrotechnology, are provided in the international standard IEC 61082-1.

Circuit diagrams are often drawn with the same standardized title block and frame as other engineering drawings.

Relay logic line diagrams, also called ladder logic diagrams, use another common standardized convention for organizing schematic drawings, with a vertical power supply rail on the left and another on the right, and components strung between them like the rungs of a ladder.

Artwork

Once the schematic has been made, it is converted into a layout that can be fabricated onto a printed circuit board (PCB). Schematic-driven layout starts with 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 automatically 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.^[9]

A generalized design flow may be as follows:

Schematic → schematic capture → netlist → rat's nest → routing → artwork → PCB development and etching → component mounting → testing

Education

Teaching about the functioning of electrical circuits is often on primary and secondary school curricula.^[10] Students are expected to understand the rudiments of circuit diagrams and their functioning. Use of diagrammatic representations of circuit diagrams can aid understanding of principles of electricity.

Principles of the physics of circuit diagrams are often taught with the use of analogies, such as comparing functioning of circuits to other closed systems such as water heating systems with pumps being the equivalent to batteries.^[11]

Related Research Articles

A logic gate is a device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has, for instance, zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device.

<span class="mw-page-title-main">Resistor</span> Passive electrical component providing electrical resistance

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements, or as sensing devices for heat, light, humidity, force, or chemical activity.

<span class="mw-page-title-main">Schematic</span> Representation of a system using abstract graphic symbols

A schematic, or schematic diagram, is a designed representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the schematic is intended to convey, and may include oversimplified elements in order to make this essential meaning easier to grasp, as well as additional organization of the information.

A printed circuit board (PCB), also called printed wiring board (PWB), is a medium used to connect or "wire" components to one another in a circuit. It takes the form of a laminated sandwich structure of conductive and insulating layers: each of the conductive layers is designed with an artwork pattern of traces, planes and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Electrical components may be fixed to conductive pads on the outer layers in the shape designed to accept the component's terminals, generally by means of soldering, to both electrically connect and mechanically fasten them to it. Another manufacturing process adds vias, plated-through holes that allow interconnections between layers.

In electronics, point-to-point construction is a non-automated technique for constructing circuits which was widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their introduction in the 1950s. Circuits using thermionic valves were relatively large, relatively simple, and used large sockets, all of which made the PCB less obviously advantageous than with later complex semiconductor circuits. Point-to-point construction is still widespread in power electronics, where components are bulky and serviceability is a consideration, and to construct prototype equipment with few or heavy electronic components. A common practice, especially in older point-to-point construction, is to use the leads of components such as resistors and capacitors to bridge as much of the distance between connections as possible, reducing the need to add additional wire between the components.

<span class="mw-page-title-main">Breadboard</span> Board with embedded spring clips that allows for electronics to be wired without soldering

A breadboard, solderless breadboard, or protoboard is a construction base used to build semi-permanent prototypes of electronic circuits. Unlike a perfboard or stripboard, breadboards do not require soldering or destruction of tracks and are hence reusable. For this reason, breadboards are also popular with students and in technological education.

Schematic capture or schematic entry is a step in the design cycle of electronic design automation (EDA) at which the electronic diagram, or electronic schematic of the designed electronic circuit, is created by a designer. This is done interactively with the help of a schematic capture tool also known as schematic editor.

Place and route is a stage in the design of printed circuit boards, integrated circuits, and field-programmable gate arrays. As implied by the name, it is composed of two steps, placement and routing. The first step, placement, involves deciding where to place all electronic components, circuitry, and logic elements in a generally limited amount of space. This is followed by routing, which decides the exact design of all the wires needed to connect the placed components. This step must implement all the desired connections while following the rules and limitations of the manufacturing process.

In electronics, a pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions. "Pinout" now supersedes the term "basing diagram" which was the standard terminology used by the manufacturers of vacuum tubes and the RMA. The RMA started its standardization in 1934, collecting and correlating tube data for registration at what was to become the EIA. The EIA now has many sectors reporting to it and sets what is known as EIA standards where all registered pinouts and registered jacks can be found.

CADSTAR is a Windows-based electronic design automation (EDA) software tool for designing and creating schematic diagrams and printed circuit boards (PCBs). It provides engineers with a tool for designing simple or complex, multilayer PCBs. CADSTAR spans schematic capture, variant management, placement, automatic and high-speed routing, signal integrity, power integrity, EMC analysis, design rule checks and production of manufacturing data.

<span class="mw-page-title-main">Electronic component</span> Discrete device in an electronic system

An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements. A datasheet for an electronic component is a technical document that provides detailed information about the component's specifications, characteristics, and performance.

OrCAD Systems Corporation was a software company that made OrCAD, a proprietary software tool suite used primarily for electronic design automation (EDA). The software is used mainly by electronic design engineers and electronic technicians to create electronic schematics, and perform mixed-signal simulation and electronic prints for manufacturing printed circuit boards (PCBs). OrCAD was taken over by Cadence Design Systems in 1999 and was integrated with Cadence Allegro in 2005.

XCircuit is a schematic capture program for drawing publication-quality VLSI electrical circuit schematic diagrams and related figures. It's part of the Open Circuit Design tools. It's primarily intended for ULSI/VLSI IC design and not for PCB design, the latter though is still possible. XCircuit regards circuits as inherently hierarchical and can save circuits both in PostScript (.ps) and Ngspice (.cir) netlists file formats for further processing. The program compiles PostScript files from special template-labels specified by user.

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.

The Layout Versus Schematic (LVS) is the class of electronic design automation (EDA) verification software that determines whether a particular integrated circuit layout corresponds to the original schematic or circuit diagram of the design.

Perfboard is a material for prototyping electronic circuits. It is a thin, rigid sheet with holes pre-drilled at standard intervals across a grid, usually a square grid of 0.1 inches (2.54 mm) spacing. These holes are ringed by round or square copper pads, though bare boards are also available. Inexpensive perfboard may have pads on only one side of the board, while better quality perfboard can have pads on both sides. Since each pad is electrically isolated, the builder makes all connections with either wire wrap or miniature point to point wiring techniques. Discrete components are soldered to the prototype board such as resistors, capacitors, and integrated circuits. The substrate is typically made of paper laminated with phenolic resin or a fiberglass-reinforced epoxy laminate (FR-4).

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electrical circuit. For a circuit to be referred to as electronic, rather than electrical, generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.

<span class="mw-page-title-main">Wiring diagram</span> Simplified conventional pictorial representation of an electrical circuit

A wiring diagram is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified shapes, and the power and signal connections between the devices.

This page is a comparison of electronic design automation (EDA) software which is used today to design the near totality of electronic devices. Modern electronic devices are too complex to be designed without the help of a computer. Electronic devices may consist of integrated circuits (ICs), printed circuit boards (PCBs), field-programmable gate arrays (FPGAs) or a combination of them. Integrated circuits may consist of a combination of digital and analog circuits. These circuits can contain a combination of transistors, resistors, capacitors or specialized components such as analog neural networks, antennas or fuses.

DipTrace is a proprietary software suite for electronic design automation (EDA) used for electronic schematic capture and printed circuit board layouts. DipTrace has four applications: schematic capture editor, PCB layout editor with built-in shape-based autorouter and 3D preview, component editor, and pattern editor.

References

↑ Circuit diagrams and component layouts
↑ Herzfeld, Noreen (2012). Computer Concepts and Applications. Minnesota: College of Saint Benedict/St. John's University. pp. 9[6]–9[12].
1 2 3 "Circuit Symbols". electronicsclub.info. Retrieved 2 August 2014.
↑ "It is good practice to never use a + connection with a dot. Why? The dot can disappear when the schematic is copied for the 12th time." – "Notes on Reading Schematics" Archived 2011-10-08 at the Wayback Machine
↑ "We recommend against using a 4-way connection point ... To avoid confusion, use only three-way connections." – "Design News Gadget Freak Submission Guidelines" Archived 2011-09-29 at the Wayback Machine
↑ "Wires connected at 'crossroads' should be staggered slightly to form two T-junctions" – "The Electronics Club: Circuit Symbols"
1 2 "Electronic Circuit Symbols". www.circuitstoday.com. Archived from the original on 13 October 2014. Retrieved 2 August 2014.
↑ Electronics Circuit Symbols
↑ R. S. Khandpur (2005). Printed circuit boards: design, fabrication, assembly and testing. Tata McGraw-Hill. p. 10. ISBN 978-0-07-058814-1.
↑ BBC Bitesize. Circuits. https://www.bbc.com/education/topics/zq99q6f
↑ Walker, M. D., & Garlovsky, D. (2016). Going with the flow: Using analogies to explain electric circuits Archived 2022-04-01 at the Wayback Machine . School science review, 97(361), 51–58.

External links

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[1] Circuit diagrams and component layouts

[2] Herzfeld, Noreen (2012). Computer Concepts and Applications. Minnesota: College of Saint Benedict/St. John's University. pp. 9[6]–9[12].

[electronicsclub.info-3] 1 2 3 "Circuit Symbols". electronicsclub.info. Retrieved 2 August 2014.

[4] "It is good practice to never use a + connection with a dot. Why? The dot can disappear when the schematic is copied for the 12th time." – "Notes on Reading Schematics" Archived 2011-10-08 at the Wayback Machine

[5] "We recommend against using a 4-way connection point ... To avoid confusion, use only three-way connections." – "Design News Gadget Freak Submission Guidelines" Archived 2011-09-29 at the Wayback Machine

[6] "Wires connected at 'crossroads' should be staggered slightly to form two T-junctions" – "The Electronics Club: Circuit Symbols"

[circuitstoday-7] 1 2 "Electronic Circuit Symbols". www.circuitstoday.com. Archived from the original on 13 October 2014. Retrieved 2 August 2014.

[8] Electronics Circuit Symbols

[9] R. S. Khandpur (2005). Printed circuit boards: design, fabrication, assembly and testing. Tata McGraw-Hill. p. 10. ISBN 978-0-07-058814-1.

[10] BBC Bitesize. Circuits. https://www.bbc.com/education/topics/zq99q6f

[11] Walker, M. D., & Garlovsky, D. (2016). Going with the flow: Using analogies to explain electric circuits Archived 2022-04-01 at the Wayback Machine . School science review, 97(361), 51–58.

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