The electronic color code was developed in the early 1920s by the Radio Manufacturer's Association, now part of Electronic Industries Alliance and was published as EIA-RS-279. The current international standard is IEC 60062.
Colorbands where commonly used (especially on resistors), because they were easily printed on tiny components, decreasing construction costs. However, there were drawbacks, especially for color blind people.
In the days of classical chassis televisions overheated resistors would change their color bands, making it virtually impossible to distinguish brown from red from orange.
Today, printed numbers are being used in favor of colorbands (see Other schemes below).
Color-coding of this form is becoming rarer. In newer equipment, most passive components come in surface mount packages. Many of these packages are unlabeled, and those that are normally use alphanumeric codes, not colors.
In one popular marking method, the manufacturer prints 3 digits on components: 2 value digits followed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 Ω, a capacitor marked 104 is 100 nF (10x104 pF), and an inductor marked 475 is 4.7 mH (4,700,000 nH). This can be confusing; a resistor marked 100 might seem to be a 100 Ω unit, and we must rely upon experience to interpret the marking as 10 Ω (10×100). Another way is to use the "kilo-" or "mega-" prefixes in place of the decimal point:
For 1% resistors, a three-digit alphanumeric code is sometimes used, which is not obviously related to the value but can be derived from a table of 1% values. For instance, a resistor marked 68C is 499(68) × 100(C) = 49,900 Ω. In this case the value 499 is the 68th entry of a table of 1% values between 100 and 999.
It is sometimes not obvious whether a color coded component is a resistor, capacitor, or inductor, and this may be deduced by knowledge of its circuit function, physical shape or by measurement (capacitors have nearly infinite resistance; unfortunately, so do faulty open-circuit resistors and inductors).
For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.
All coded components will have at least two value bands and a multiplier; other bands are optional (italicised below).
The Standard EIA Color Code Table per EIA-RS-279 is as follows:
|Color||1st band||2nd band||3rd band (multiplier)||4th band (tolerance)||Temp. Coefficient|
|Brown||1||1||×101||±1% (F)||100 ppm|
|Red||2||2||×102||±2% (G)||50 ppm|
Note: red to violet are the colors of the rainbow where red is low energy and violet is higher energy.
As an example, let us take a resistor which (read left to right) displays the colors yellow, violet, yellow, brown. We take the first two bands as the value, giving us 4, 7. Then the third band, another yellow, gives us the multiplier 104. Our total value is then 47 x 104 Ω, totalling 470,000 Ω or 470 kΩ. Our brown is then a tolerance of ±1%.
Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent; 6.8, 68, 680, and so forth. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colors, which make them easier to understand.
A much older resistor color coding scheme, still to be found on components in vintage radios, is known as 'body-tip-spot'. Here the color of the resistor body was the first digit, the color of one tip or end of the resistor was the second, and the color of the spot on the body was the multiplier.
The tolerance codes, gold, silver, and none, are not usually included in the mnemonics; one extension that includes them is:
Since B can stand for both "black" and "brown", variations are formed such as "black boys rape only young girls...".
Humorous, offensive, or sexual mnemonics are more memorable (see mnemonic), but these variations are often considered inappropriate for classrooms, and have been implicated as a sign of sexism in science and engineering classes. (Dr. Latanya Sweeney, associate professor of computer science at Carnegie Mellon, a black woman, mentions the mnemonic as one of the reasons she felt discriminated against and dropped out of MIT in the 1980s to form her own software company.)
An easily-remembered and inoffensive mnemonic that was current in at least the early 1960s is:
An alternative way to recall that black comes before brown in the color code is to use the position of white at the end of the color code as a key to remember that its opposite, black (and not brown), is at the beginning, or to simply make a connection between black and zero (emptiness, nothingness, or absence of color).
From top to bottom:
Note: The sizes of the resistors depend only on the power they can dissipate, and do not affect their value.