Talk:Circuit diagram

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject South Africa / PSP SA (Rated Start-class)
WikiProject icon This article is within the scope of WikiProject South Africa, a collaborative effort to improve the coverage of South Africa on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 ???  This article has not yet received a rating on the project's importance scale.
Taskforce icon
This article is supported by Wikipedia Primary School project.
WikiProject Electronics (Rated Start-class, High-importance)
WikiProject icon This article is part of WikiProject Electronics, an attempt to provide a standard approach to writing articles about electronics on Wikipedia. If you would like to participate, you can choose to edit the article attached to this page, or visit the project page, where you can join the project and see a list of open tasks. Leave messages at the project talk page
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 High  This article has been rated as High-importance on the project's importance scale.

Page name[edit]

I moved this page back to its current location because 'circuit diagram' is far, far, far more common than 'electrical diagram' →Raul654 01:03, Mar 13, 2005 (UTC)

Ok. I just figured it was more accurate. "Circuit" could mean more than just electrical. I hope moving the Category "Circuit diagrams" to "Electrical diagrams" was not bad... That took a while.  :-\ - Omegatron 02:03, Mar 13, 2005 (UTC)

e.j. gallaher Nov 3, 2005 I do not have a contribution, but a question about the historicial basis of electronic circuit diagrams, or schematics.

This is more of a 'history' question, or a 'linguistic' question than anything else.

I realize why a resistor is diagrammed as it is, and why a capacitor is diagrammed as it is. What I would like to know is "Who conceived of the -concept- of developing the symbols in the first place, and how did the development of the electronic schematic evolve?

For example: It is difficult, if not impossible, to describe the structure and function of a simple transformer, full-wave bridge rectifier, and capacitive filter in a simple power supply, IN THE ABSENCE of the familiar schematic diagram. It could therefore be argued that the intellectual development of the diagram itself was a necessary component of the development of electronic 'thinking'.

We could make the same argument regarding music notation. Folk music has been around since prehistoric times. We can imagine several singers and/or musicians getting together, conceiving of a simple melody, and then developing various rhythms and simple harmony. This could be done from memory, and the results could be passed along to other musicians via direct contact. However, it is impossible to imagine symphonic music developing in this manner, in the absence of a written symbolic language.

Can anyone suggest that Beethoven might have composed each of his symphonies in his head, and then taught the parts to the violins, violas, clarinets, flutes, horns, etc. IMPOSSIBLE! Therefore, the NOTATION itself ALLOWED musical thinking to be taken to new heights. I suggest the same is true with electronic notation, but I find virtually nothing about this topic, wherever I look, or inquire.

Any ideas?

Interesting question. According to logical form, Aristotle was the first to use abstract "schematic" letters to represent any one of a number of concrete situations. I suppose this idea later developed into the idea that one abstract electronic schematic could represent any of a number of concrete situations. Perhaps that is going too far back in time. Please tell me if you find more information on the history of circuit diagrams. Also please tell me if you find a good name for this more general field of "how notation develops, and how creating and improving notation allows people to do things that were impossible before". Such a field would, of course, include the various numeral systems, alphabets, Lewis structure, Feynman diagrams [1], etc.. -- 05:40, 20 August 2006 (UTC)

Closely after the creation 1906 of the International Electrotechnical Commission (IEC) two of the first four topics for work were "nomenclature" and "symbols". That terminology comes first is natural; without agreed definitions of concepts with associated terms no sensible communication is possible. But it is interesting to note that symbols comes closely related as the second. At this time the term symbol included both "letter symbol" (used for quantities and units) and "graphical symbol" used for documentation (later also for use on equipment). In fact electrotechnical documentation seems for along time have been synonymous with "application of symbols"; at least the first published standards have such a focus. In IEC were later technical committees created for different subjects i.a.: TC1 for Terminology, TC3 for Graphical symbols and TC25 for Quantities, units and their letter symbols. Some more history is available here:

As the commission could agree on symbols as topic for work symbols and circuit diagrams must have been around for some time already 1906. Pasvensson 19:50, 19 September 2007 (UTC)

Popular culture[edit]

"In the animated television series Futurama, set in the 31st century, circuit diagrams serve as pornography for robots." Very amusing, but does this really belong here?


  • Schematic and circuit diagram should remain as separate articles, in my opinion. There are many types of schematics which have nothing to do with circuits. Circuit diagram is certainly a big enough topic to desreve an article of its own. ike9898 15:02, 9 January 2007 (UTC)



the symbol for a resistor is a box. Dunno if that is just english but it should be included --Slogankid 15:05, 9 January 2007 (UTC)

Incorrect. That is a comon layout symbol for resistors, but is almost never used in schematics. (talk) 22:15, 9 December 2007 (UTC)
Sorry, That was correct for the Brits, although the box is a really poor symbol choice, as it could very easily be mistaken as a symbol for an unknown 2 pin device. (talk) 22:19, 9 December 2007 (UTC)
Actually the box symbol is the International Electrotechnical Commission's symbol for a resistor —Preceding unsigned comment added by (talk) 13:10, 9 October 2009 (UTC)


I believe that schematics, although used to describe circuit diagrams, is too vague. A schematic can be any rough representational diagram. I feel that 'Electronic Schematic' may be more suitable. ps... I agree with the above bit about box resistors. The English way is boxes, th e American, and more common way, is to use zig-zags.

Jdedmond 20:04, 29 January 2007 (UTC)

verification needed[edit]

The letters that precede the numbers were chosen in the early days of the electrical industry, even before the vacuum tube (thermionic valve), so "Q" was the only one available for semiconductor devices in the mid-twentieth century ...

Does anyone have information on this letter choosing? What do all the other letters of the latin alphabet stand for then? --Abdull 09:36, 16 March 2007 (UTC)

I don't know if "Q" was the only one available.
But certainly "T" was already taken by "transformer".
I'm going to remove that sentence. Given that the invention of integrated circuits post-date transistors, clearly U must still have been available as well. I'm guessing here, but it seems likely that whomever it was that decided (the International Electrotechnical Commission?)on the symbol simultaneously decided on the letter to be used for descriptors. The symbols look kind of like a Q, so they probably said "hey, let's use Q". CruiserBob (talk) 17:59, 14 September 2009 (UTC)

Where are the american designation codes?[edit]

Well, where are they? Article mentions that the euro/aussie codes differ, but does not show any of the american codes. TheJalAbides 19:01, 16 March 2007 (UTC)

Off the top of my head (please help me find proper references before we move it into the article), the common component designators here (I'm in the U.S.) are: -- 05:53, 10 June 2007 (UTC)

  • A ( sometimes used to mark the Anode end of a D diode or L LED )
  • B battery
  • C capacitor
  • D diode (sometimes LED)
  • E
  • F fuse
  • G
  • H
  • I ( looks like "1" used to mark pin 1 of components where that matters -- U and J and others )
  • J jack
  • K
  • L lamp or inductor (sometimes LED)
  • M motor
  • N
  • O
  • P plug
  • Q transistor
  • R resistor
  • S switch
  • T transformer
  • U any kind of integrated circuit. A 3 pin voltage regulator, a 144 pin microprocessor, etc.
  • V voltage regulator
  • W
  • X "xtal" crystal oscillator
  • Y
  • Z zener diode

One might expect inductors to always start with "I". But no -- inductors always start with "L". I don't know why.

When someone refers to, say, "D13-A", that means the anode of the diode with the "D13" written on the PCB next to it.

When someone refers to, say, "U2-15", that means pin 14 of the chip with the "U2" written on the PCB next to it. (Pin 1 should be clearly marked, and IC chips are always numbered counter-clockwise from pin 1 when looking at the top surface -- except for BGAs. Alas, J jacks and P plugs are not always numbered counter-clockwise.)

-- 05:53, 10 June 2007 (UTC)

the prob you will have is the standards do not exist or when thay do thay are not alwase folowed.
J is ues for mosfets and jfets
P ive seen for use on filters
D would be diodes including LEDS
L is alwase inductor and never LED
LS and S as speaker S should be switch however
ive never herd of using V for voltage regulator instead U is used for regulators or basicly any silicone package thats not a diode mosfet BJT Jfet scr scs triac... aka 2 and 3 pin discrete devices.
o btw zenner diodes use D rather than Z only the symbol changes althow more discriptive BOM lists is alwase a +.
also ive seen J used for cable connectors on motherboards and JP used for jumpers on same.

y is used for ceramic resonators and ive also seen it use for crystals but more likely it was a universal socket a crystal requires 2 caps on each side to ground, ceramic resonator is same pin out only it needs center pin grounded so a 3 hole pad area is set up for circuits that can use either.

BZ buzzer , M and MV for MOV surge supressors(see any APC circut board)
Eadthem (talk) 02:53, 19 December 2007 (UTC)

According to Inductance, the use of "L" for an inductor may honor Heinrich Lenz who made contributions to the understanding of inductance. Philhower (talk) 19:37, 14 October 2008 (UTC)
I never really thought about why L. I assumed it was for the Looped wire that makes a coiL. (talk) 16:08, 18 November 2010 (UTC)

Addition of references to International standards[edit]

I have added references to the International standards IEC 61082-1, IEC 60617 DB and IEC 61346. IEC standards are issued by the International Electrotechnical Commission and are usually the basis for official National standards.

IEC 61082-1 (Rules for the preparation documents used in electrotechnology, Part 1: General rules) consisted earlier of 4 parts, but has recently been consolidated into one.

The old IEC standard on graphical symbols numbered IEC 617 (consisted of 13 parts) is nowadays replaced by IEC 60617 DB (Graphical symbols for diagrams). DB indicates that it is a standard in database format. It contains some 1750 valid symbols. It is accessible via Internet, on a subscription basis.

IEC 61346 (Industrial systems, installations and equipment and industrial products – Structuring principles and reference designations) consists of several parts, of which the most important are Part 1 (Basic rules) and Part 2 (Classification of objects and codes for classes).

The codes listed in the article does not correspond entirely to those of Part 2 of that standard.

IEC 61346 is, by the way, under revision in collaboration with ISO and will be renumbered to IEC-ISO 81346.

For more information on the work on these standards, please refer to, the site of the technical committee TC3 (Information structures, documentation and graphical symbols) responsible for the actual standards, and to the overall web site of IEC

reactions to circuit diagrams[edit]

Would the general Wikipedia reader would be interested in knowing that circuit diagrams stir surprisingly strong emotions in some people?

  • "if you’re selling to engineers or IT folks, nothing says loving like a beautiful schematic. We love schematics!"[2]
  • "beautifully done schematic"[3]
  • "a beautiful schematic shows ..."[4]
  • "I got this beautiful schematic"[5]
  • "A lovely and visually symmetrical schematic."[6]

and the opposite emotion:

  • "those abhorrent European-style circuit symbols." [7]
  • "It takes a computer to create such god awful ugly schematics"[8]

-- (talk) 04:24, 13 September 2008 (UTC)

Some people have strong reactions to the oddest things. I don't think this is necessary to mention in a general article and should be discussed in a more appropriate article. --Wtshymanski (talk) 15:06, 13 September 2008 (UTC)

Not synonymous terms[edit]

A wiring diagram is not the same as a schematic diagram. If you're trying to illustrate the concept and logic of a system, you would use a schematic. If you're trying to build a control panel, you'd hand a wiring diagram (or these days, a wire list) to the panel shop to have them build it. A wiring diagram shows the wires and interconnections but may not give much of the sequence and operation of the circuit. A schematic may not clearly show which wires are bundled in which cables, for example. Sometimes a schematic will carry more of the information associated with a wiring diagram such as terminal numbers (especially such things as intermediate terminal blocks) but not always. --Wtshymanski (talk) 13:36, 27 August 2009 (UTC)

How old is old?[edit]

For the last 35 years I learn to use the "old" CAD symbols for non-CAD drawings, with the notion that the "old non-CAD symbols" were used by our grandparents and are now obsolete. — Preceding unsigned comment added by (talk) 15:58, 31 March 2015 (UTC)