INTRODUCTION

Back in May ’97, I started writ-ing regular ‘circuit application’ fea-ture articles for Nuts & Volts maga-zine. All of these articles are specif-ically aimed at experienced designengineers and competent electron-ics enthusiasts (rather than atnovices or complete beginners),and are unusual in two specialrespects.

They are unusual, first,because most of them carry (onaverage) about 20 illustrations orpractical circuit diagrams, and sec-ond, because all of the circuit dia-grams use International style —rather than US Customary — circuitsymbols and component notations.

All of these articles have beenwell received by most Nuts & Voltsfans, but some readers (who admitto being electronics novices) havecomplained that they are quitebemused by the component nota-tions that I use in these articles. Isuspect that quite a few other Nuts& Volts fans may feel the same wayso, in this special article, I aim toexplain the operation of theInternational style electronic circuitdiagram system, and to explain thesystem’s advantages over the USCustomary system. This is a fairlycontroversial subject and mayannoy some readers, so I will startoff by presenting my qualificationsfor writing about it, as follows:

MY QUALIFICATIONS

I have been an electronicsdesign engineer and writer/authorfor over 30 years. During that peri-od, I have — amongst other things

— been editor or technical editor offour different electronics maga-zines, have written about 2,000technical articles, and have written31 electronics engineering books.Many of my magazine articles arepublished internationally, and — invarious periods — have appearedregularly in magazines in the UK,Germany, Holland, Australia,Canada and the USA.

Of my 31 books, two were firstpublished in Germany, and the restin the UK; several were later pub-lished in the USA. Between them,these books have been translatedinto about a dozen different lan-guages (often with suitably modi-fied circuit dia-grams), includingRussian, Hindus-tani, and mostmajor Europeantongues.

T h r o u g h o u tthe past five years,I have producedmost of the art-work and circuitdiagrams that ac-company mybooks and maga-zine articles(including thoseused in Nuts &Volts), using aCorel DRAW 3 art-work/CAD pack-age and my privatesymbols library. Igenerate an aver-age of about 350diagrams a year,and have thus pro-duced about 1,750technical illustra-tions and diagramsin the past fiveyears.

As a conse-quence of all theabove, I have lots of professionalexperience in the technical publish-ing business and in generatingmodern circuit diagrams, and amfamiliar with many of the differentelectronic circuit symbol and nota-tion systems that are used in vari-ous parts of the world and with theirspecific advantages and disadvan-tages compared to other systems.

TYPICAL CIRCUIT DIAGRAMS

In the western world, most

major industrial countries havetheir own individual preferred stylesfor electronic circuit symbols andnotations, but these styles are nottoo rigidly applied and often varyconsiderably between one techni-cal publisher and another, accord-ing to the ‘house style’ of the indi-vidual publishing company. In theUSA, for example, the so-called‘US Customary’ system is normallyused, but the precise details of thesystem vary significantly betweendifferent electronics magazines.

Figures 1 to 5 show examplesof how exactly the same circuit dia-gram can vary when published byparticular electronics magazines in

particular parts of thewestern world. The circuitis that of a simple LM386audio power amplifier,with its voltage gain set atx200 by C4 and with itsoutput protected by theC3-R1 Zobel network andloaded by an eight-ohmspeaker.

Figure 1 shows thediagram drawn using thefamiliar US Customarysystem, using the basichouse style of Electronics

Now magazine, and Figure 2shows the same diagram drawn inthe house style of the Germanelectronics magazine Elrad, whichuses a simple rectangular symbol(rather than a zig-zag) to representa resistor.

Regarding the German capaci-tor symbols, the two parallel linesused to represent C1 and C3 indi-cate that these are ordinary non-electrolytic components, and theblack and white rectangles used torepresent C2 and C4 indicate thatthese are electrolytic capacitors;the ‘+’ signs associated with C2 andC4 indicate that the capacitors arepolarized types, and that the white

Reprinted from December 1998 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 1

ELECTRONIC CIRCUIT SYMBOLS & NOTATIONS

ΩRay Marstonlooks at somecontroversialaspects ofmodern circuitsymbology inthis specialfeature article.

by Ray Marston

Figure 5. Circuit drawn in typicalInternational style.

Figure 4. Circuit in the house style ofElectronics World magazine (UK).

Figure 3. Circuit in the house style of Electronics Today International

magazine (UK).

Figure 2. Circuit in the house style ofElrad magazine (Germany).

Figure 1. Circuit in the house style ofElectronics Now magazine (USA).

terminal is positive.In the UK, British electronics

magazine sales are dominated bysix popular titles. Half of these usethe zig-zag resistor symbol in theircircuit diagrams, and half use thesimple rectangular symbol. Figure 3shows the Figure 1 diagramredrawn in the house style of one ofthe most popular British electronicsmagazines, Electronics TodayInternational, which uses the simplerectangle to represent a resistor,and uses two black rectangles torepresent an ordinary non-elec-trolytic capacitor.

The most prestigious Britishelectronics magazine is ElectronicsWorld, which is aimed directly atprofessional engineers and man-agers; it has its own basic housestyle for circuit diagrams, but variesthe style slightly from article to arti-cle. Figure 4 shows Figure 1redrawn in this magazine’s basichouse style; note the awkward mix-ture of upper-case and subscriptcharacters used to denote compo-nent numbers, etc.

Finally, Figure 5 shows Figure 1drawn in my own particular versionof the International circuit diagramstyle (which I use in my Nuts & Voltsarticles), in which resistors aredrawn as zig-zags, capacitors are in

simplified European style, and com-ponent values are given in formal‘International’ style, which isexplained in a later major section ofthis article.

Note in Figures 1 to 5 that allfive basic diagrams are quite easyto understand, in spite of the varia-tions in the styles of the symbolsused to represent resistors, capaci-tors, ground points, and loudspeak-ers. Also note that the variableresistor is notated by RV (Resistor,Variable) in the four non-US dia-grams, but by a simple R in Figure1. Finally, note that the Figure 2 to 5diagrams use a plain R instead ofthe symbol to indicate a resistor’svalue in ohms, and (in Figures 2and 4) use the symbol only to indi-cate the loudspeaker’s nominalimpedance value.

The easily-understood Figure 1to 5 circuits are analog designs.Foreign digital designs can be farharder to understand. Figure 6, forexample, shows some of the crazyofficial symbols used to representsimple logic gates in Europe. Inpractice, most European electron-ics book and magazine publisherssensibly adhere to the AmericanMIL/ANSI symbol system, which isalso used in the normal‘International’ diagram system.

For most American readers, theonly problems presented by thenon-US Figure 2 to 5 diagramsrelate to the International compo-nent value notation systems thatthey use, which all notate the 10resistor as 10R, and notate0.047µF capacitor C3 as 47n (theodd 220u — rather than 220µ —notation used on C4 in Figure 3 issimply a house style peculiarityused by one UK magazine). Beforeexplaining how the Internationalnotation system works, I will explainwhy it was developed.

EVOLUTION OF THEINTERNATIONAL SYSTEM

Prior to the mid 1970s, theelectronic component notation sys-tems used by most European coun-tries were similar to the present USCustomary system and were loose-ly based on the metric scientificnotation system that — in 1960 —became officially known as SI(Système Internationale d’Unités).

In the 1960s, however, majordevelopments in the semiconductorindustry resulted in a great increasein the complexity of practical circuitdesigns, and industry and com-merce began looking for ways of

producing the result-ingly complex circuitdiagrams and literaturewith greater efficiency.

Matters reached ahistoric peak in 1975when the BritishStandards Institute(BSI) published —after a very long periodof study and consulta-tion — a list of recom-mendations concern-ing this subject.

Many of the 1975BSI recommendations— particularly thoserelating to the use ofnew digital circuit sym-bols — were pretty stu-pid, and were rejectedby most of the elec-tronics industry, butthose relating to aninternational system ofelectronic component-value notation wereexcellent, and weresoon adopted by mostof the world’s industrialnations, with thenotable exception ofthe USA.

This new notationsystem was, in effect,an improved andstreamlined version ofthe existing SI-basedsystem, and was thusquite easy to learn.When its basic form

was first specified, it was requiredto be designed as a simple easily-printed code that indicates an elec-tronic component’s value clearly,briefly, without ambiguity, and with aminimum loss of clarity if poorlyprinted.

This last requirement immedi-ately ruled out the use of decimalpoints in the new code system, andthe requirement for brevity calledfor (1) the elimination of all super-fluous information from the code,and (2) for sensible compression ofthe remaining data.

Regarding point (1) in the‘brevity’ requirement, note that incircuit diagrams, when indicatingthe value of a symbolic resistor,capacitor, or inductor, it is self-evi-dent that the component’s value isexpressed in basic units of ohms,Farads, or Henrys, and the newcode’s design specification thusdemanded the elimination of thissuperfluous ‘postscript’ data fromthe printed code when used in cir-cuit diagrams (but not necessarily innormal printed text).

Regarding point (2) in the‘brevity’ requirement, this was to beaided by using a fixed three-decade spacing between the deci-mal ‘multiplier’ units used to indi-cate a component’s value.

Figure 7 lists the range of dec-imal multiplier units — using basicSI scientific notation and three-decade spacing — that are normal-ly used in electronics, together withtheir normal prefixes, etc., andFigure 8 shows how they areapplied in the modern USCustomary notation system (whichwas also widely used in pre-1975Europe).

Note in Figure 8 that the USCustomary system uses three-decade multiplier spacing whennotating values of resistance,inductance, frequency, and time,but inexplicably uses six-decadespacing (between µF and pF) whennotating values of capacitance.This six-decade spacing is a majorcause of the cumbersome capaci-tance-value notations (such as0.001µF) that often appear in UScircuit diagrams.

These, then, were the basicideas behind the creation anddevelopment of the 1975 BSI com-ponent notation system, whichtoday is known as the ‘International’system. Let’s now look at thedetails of the modern version of thissystem.

THE INTERNATIONALSYSTEM

RESISTANCE NOTATION

The standard unit of resistanceis the ohm, named after a Bavarian,George Simon Ohm who, in 1827,

Reprinted from December 1998 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 2

Figure 6. A selection of widely used logic symbols.

ELECTRONIC CIRCUIT SYMBOLS & NOTATIONS

published the results of hisresearch into electrical resis-tance and whose name is com-memorated by the symbol Ω(omega), which is the Greekequivalent of the Bavarian letterÖ. In 1975 (prior to the advent ofthe wordprocessor and CADdrawing), the symbol Ω was notcarried on normal typewritersand was time-consuming to pro-duce using normal drawing tech-niques.

Consequently, in 1975, theBSI recommended that the sym-bol Ω should no longer be usedon circuit diagrams as a postscriptwhen denoting resistance values,that units of resistance should benotated by the capital letter R, thatthousands of units be notated bythe lower-case letter k (for kilohm),and millions of units be notated bythe upper-case letter M (formegohms). Thus, in this system,47Ω, 47kΩ, and 47MΩ become47R, 47k, and 47M.

CAPACITANCE NOTATION

The standard unit of electricalcapacitance is the Farad, repre-sented by the symbol F. In elec-tronics, the Farad is too large aunit for general use and, prior to1975, most capacitors had valuesthat were expressed in units of amillionth of a Farad (µF) or a mil-lionth of a millionth of a Farad (pF).Thus, 1µF equals 1,000,000pF.This six-decade space betweenbasic multiplier units obviouslyresults in excessively long compo-nent notations, and BSI recom-mended that this problem be elim-inated by reducing the spacingbetween multiplier units to threedecades, by introducing a unitknown as the nanofarad (fullynotated as nF), and equal to1000pF. Thus, 1nF equals 0.001µF,and 1000nF equals 1µF.

In circuit diagrams, when indi-cating the value of a capacitor, it isself-evident that the component’svalue is expressed in Farads, andit is thus superfluous to re-statethe fact in the diagram.

Consequently, the BSI recom-mended that, for component nota-tion purposes, the symbol F shouldno longer be used on circuit dia-grams as a postscript when denot-ing capacitance values, and that thescientific symbols µ, n, and p beused as basic multiplier units. Thus,in this system, 4,700µF, 47µF,0.047uF, and 47pF become 4,700µ,47µ, 47n, and 47p.

INDUCTANCE NOTATION

The standard unit of electricalinductance is the Henry, represent-ed by the symbol H. In circuit dia-grams, when indicating the value of

an inductor, it iss e l f - ev i d e n tthat the com-ponent’s valueis expressed inHenrys, and itis thus super-fluous to re-state the fact inthe diagram.Consequently,in 1975, theBSI recom-mended that —on circuit dia-grams — thecapital letter Hshould only beused to notateactual units ofi n d u c t a n c e ,that thou-sandths ofunits be notat-ed by thelower-case let-ter m (= milli-henry), andmillionths ofunits be notated by the symbol µ (=microhenry). Thus, in this system,47H, 47mH, and 47µH become47H, 47m, and 47µ.

DECIMAL POINTS

Decimal points sometimesbecome so severely degraded dur-ing the printing process that theycease to have a final practicalvalue. As an example of thisprocess, take the case of the deci-mal point associated with C1 inFigure 1. I originally generated thisdiagram in Corel DRAW vector for-mat, with the C1 notations set inArial text at 10-point size, underwhich conditions the decimal pointtakes the form of a 0.3mm x 0.3mmsquare.

To prepare this vector diagramfor minimum-cost publishing, I thenconverted the drawing to Tiff 5.0bitmap format at 300 dpi (in whichthe decimal point measures 4 x 4pixels), and then scaled the bitmapto the ‘77% of original’ size at whichit is meant to be printed in Nuts &Volts (at which scale the point sizereduces to 3 x 3 pixels). The com-

plete bitmap was then printed outon high quality paper using aLaserjet printer and mailed off toNuts & Volts.

On receipt of my artwork, Nuts& Volts scanned my bitmap into themagazine’s printer, which thentransferred the diagram to the print-ed page, where the decimal pointprobably measures 2 x 2 pixels,i.e., its size has fallen from 16 pix-els to 4 pixels in the productionprocess.

Thus, this minimum-cost art-work production process results insevere loss of the decimal point’sdefinition. This problem can bereduced, at a much increased cost,by supplying the publisher with adisk copy of the full-scale Tiff 5.0bitmap, which can then be fed — atan appropriate scale — directly intothe publisher’s printer, but even thisprocess results in a final decimalpoint size of no more than 9 pixelsat 77% scale.

The important thing to notefrom the above is that decimalpoints often become severelydegraded during the printingprocess and, in their 1975 report,

the BSI recommended that, forcomponent/parameter value nota-tion purposes, the decimal pointshould no longer be used andshould be replaced by the basiccomponent/parameter multipliersymbol (such as V, k, n, µ, etc.)applicable to that value. Thus, inthis system, values such as 4.7V,4.7kΩ, and 4700pF (= 0.0047µF or4.7nF) become 4V7, 4k7, and 4n7.

AN OVERVIEW

There are four major differ-ences between the Internationaland US Customary notation sys-tems, and two of these are illus-trated in Figure 9, which showsthe multiplier symbols that areused in the International system;compare this diagram with that ofFigure 8, and note that theInternational system uses thesymbol R to indicate basic resis-tance units, and uses the symboln to indicate ‘thousandths of a µF’capacitance units.

Of the remaining two differ-ences, one is that — in circuit dia-grams — the International system

Reprinted from December 1998 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 3

Figure 10. A selection of US Customary notations and their International system equiv-alents, reproduced at 100%, 77%, 66%, and 50% scales.

Figure 9. Multiplier symbols used inthe International notation system.

Figure 8. Multiplier symbols used inthe US Customary notation system.

Figure 7. Decimal multiplier scientific

notations.

ELECTRONIC CIRCUIT SYMBOLS & NOTATIONS

does not use basic component‘type’ symbols (such as Ω, F, or L)as component postscript notations,and the other is that theInternational system used thecomponent’s multiplier symbol inplace of a decimal point in theactual component-value notation.

SPECIAL NOTES

Note that, although the BSI‘International’ style of parameter-value notation was originally devel-oped in the days when text wastypewritten and circuit diagramswere hand-drawn, it still has greatvalidity today, when text is generat-ed on a wordprocessor and draw-ings are generated via a CADpackage.

The US Customary notation‘0.0047µF,’ for example, looksclumsy, takes up lots of valuabletext or drawing space, and takes10 keystrokes to produce; theequivalent ‘4n7’ International nota-tion is, on the other hand, crystalclear, takes up a minimum ofspace, and takes only three key-strokes to produce.

Most real-life International

component notation codes consistof two or more digits plus one sym-bolic ‘multiplier’ notation; thus, inFigure 5, resistance values of 10kand 10R and capacitance values of100n, 10µ, and 220µ are used.When below-unity values such as0.1 or 0.5µH occur, they are notat-ed 0R1 or 0µ5 in the Internationalsystem. Note that the use of a two-digit code loosely implies a two-digit degree of component preci-sion; thus, if an 8Ω resistor is to beused in a semi-precision applica-tion, its value should be notated8R0, but if it is only a very approxi-mate value (such as a speakerimpedance value), it can legiti-mately be simply notated as 8R.

The most important real-lifetests regarding ‘International’ ver-sus ‘US Customary’ componentvalue notation systems are thoserelating to ease-of-use and finalappearance on the printed page.You can only pass a fair commenton the first of these tests by mak-ing a genuine effort to get used tothe International system, which isused by most engineers and elec-tronics hobbyists throughoutEurope and much of the rest of the

world.Regarding the second test,

you can make a quick decision onthis with the help of Figure 10,which shows a matching selectionof International and US Customarycomponent notations reproducedin extra-high-quality at 100% scale(full size), at 77% scale (the normalNuts & Volts size), at 66% scale(the normal paperback handbooksize), and at 50% scale (the nor-mal small pocketbook size). Notethe way in which the decimal points

degrade in the smaller-scale USCustomary notations.

I think the International nota-tion system is the best of the two,and to help novice readers getused to it, future articles will, whenappropriate, carry a small‘Beginner’s Guide’ box, giving aconcise explanation of theInternational notation system (seeFigure 11). If lots of readers contin-ue to have problems, I will revert tothe US Customary notation systemin a future series. NV

Reprinted from December 1998 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 4

Beginner’s Guide to Component NotationsIn this article, the values of resistors and capacitors, etc., are notated inInternational — rather than US Customary — style.

In resistance notation, the symbol R represents units of resistance, k representsthousands of units, and M represents millions of units. Thus, 10R = 10Ω, 47k =47kΩ, 47M = 47MΩ.

In capacitance notation, the symbols µ, n (= 1000pF), and p are used as basicmultiplier units. Thus, 47µ = 47µF, 47n = 0.047µF, 10n = 0.01µF, and 47p = 47pF.

In the International notation system, decimal points are not used in notations andare replaced by the multiplier symbol (such as V, k, n µ, etc.) applicable to theindividual component value. Thus, 4V7 = 4.7V, 4k7 = 4.7kΩ, 4n7 = 4.7nF, and1n0 = 1.0n.

Figure 11. Beginners Guide box, giving a concise explanation ofthe International notation system.

ELECTRONIC CIRCUIT SYMBOLS & NOTATIONS