THE RESISTOR COLOUR CODE
Here is an industry-standard mnemonic e-mailed by Bill Woods for recalling the order and value of colour-markings on resistors. Although a politically/socially dubious phrase, it has nevertheless served to teach budding electronics engineers the code successfully for many years.
"Black Boys Rape Our Young Girls, But Violet Gives Willingly."
The first letter of each word matches the first letter of each colour in an order which is also numeric (black being zero, brown being one, red two, etc).
Black (=0), Brown (=1), Red (=2), Orange (=3), Yellow (=4), Green (=5), Blue (=6), Violet (=7), Grey (=8), White (=9).
Resistors are usually marked with a resistor colour code consisting of coloured bands (normally four) that surround the body of the resistor and help to identify the value (in ohms), the tolerance (in percent), and in some cases the reliability rating. Most resistors have a typical 5%-10% tolerance value.
Normally only four color bands are shown on the resistor (offset towards one end, being the reading start-point) to give a "first digit" (1-9), a "second digit" (0-9), a "multiplier" (0-9) and a "tolerance" (5, 10 or 20%). Each colour represents a number 0-9, so that for example the bands "Yellow-Violet-Red-Brown" represent "4"+"7"+"00" +"2"%, or a 4700 Ohm resistor with 2% tolerance.
The full resistor chart is:
Note that the first band will always be some color other than black(=0). One rare exception is when you have a "Zero"(0) ohm resistor (ie. a solid wire or jumper), when only one black band will exist on the resistor.
For the tolerances, notice that only a few values are used. Also gold and silver are used primarily for tolerance and resistor values of less than 10 ohms (ie. "Yellow-Violet-Gold-Silver" represents 4+7,(x0.1),+10%, or a 4.7 Ohm resistor with 10% tolerance).
The most popular resistor values used are rounded decimal (ie. 10 ohms, 100 ohms etc), otherwise values of 22xx, 33xx, 47xx and 56xx are normally used (because other values can be approximated by using combinations, eg. a resistance of 82 ohms can be created using 47 and 33 ohm resistors). With such a limited range, if you memorize the color values for these four sequences (22,33,47,56) then you only need to decode the multiplier band (ie. the 3rd band).Alternatives:
For the mnemonic itself, a less morally dubious version has been e-mailed by Adam Davies:
" Bad Booze Rots Our Young Guts, But Vodka Goes Well!"
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