How to use Resistors in circuits
Resistor Colour Coding uses coloured bands to easily identify a resistors resistive value and its percentage tolerance.
There are many different types of Resistor available which can be used in both electrical and electronic circuits to control the flow of current or to produce a voltage drop in many different ways. But in order to do this the actual resistor needs to have some form of “resistive” or “resistance” value. Resistors are available in a range of different resistance values from fractions of an Ohm ( Ω ) to millions of Ohms
Obviously, it would be impractical to have available resistors of every possible value for example, 1Ω, 2Ω, 3Ω, 4Ω etc, because literally tens of hundreds of thousands, if not tens of millions of different resistors would need to exist to cover all the possible values. Instead, resistors are manufactured in what are called “preferred values” with their resistance value printed onto their body in coloured ink.
The resistance value, tolerance, and wattage rating are generally printed onto the body of the resistor as numbers or letters when the resistors body is big enough to read the print, such as large power resistors. But when the resistor is small such as a 1/4 watt carbon or film type, these specifications must be shown in some other manner as the print would be too small to read.
So to overcome this, small resistors use coloured painted bands to indicate both their resistive value and their tolerance with the physical size of the resistor indicating its wattage rating. These coloured painted bands produce a system of identification generally known as a Resistors Colour Code.
An international and universally accepted resistor colour code scheme was developed many years ago as a simple and quick way of identifying a resistors ohmic value no matter what its size or condition. It consists of a set of individual coloured rings or bands in spectral order representing each digit of the resistors value
The resistor colour code markings are always read one band at a time starting from the left to the right, with the larger width tolerance band oriented to the right side indicating its tolerance. By matching the colour of the first band with its associated number in the digit column of the colour chart below the first digit is identified and this represents the first digit of the resistance value.
Again, by matching the colour of the second band with its associated number in the digit column of the colour chart we get the second digit of the resistance value and so on. Then the resistor colour code is read from left to right as illustrated below
Then we can summerise the different weighted positions of each coloured band which makes up the resistors colour code above in the following tables.
The Resistor Colour Code system is all well and good but we need to understand how to apply it in order to get the correct value of the resistor. The “left-hand” or the most significant coloured band is the band which is nearest to a connecting lead with the colour coded bands being read from left-to-right as follows:
Digit, Digit, Multiplier = Colour, Colour x 10 colour in Ohm’s (Ω)
For example, a resistor has the following coloured markings;
Yellow Violet Red = 4 7 2 = 4 7 x 102 = 4700Ω or 4k7 Ohm
The fourth and fifth bands are used to determine the percentage tolerance of the resistor. Resistor tolerance is a measure of the resistors variation from the specified resistive value and is a consequence of the manufacturing process and is expressed as a percentage of its “nominal” or preferred value.
Typical resistor tolerances for film resistors range from 1% to 10% while carbon resistors have tolerances up to 20%. Resistors with tolerances lower than 2% are called precision resistors with the or lower tolerance resistors being more expensive.
Most five band resistors are precision resistors with tolerances of either 1% or 2% while most of the four band resistors have tolerances of 5%, 10% and 20%. The colour code used to denote the tolerance rating of a resistor is given as:
Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %
If resistor has no fourth tolerance band then the default tolerance would be at 20%.
It is sometimes easier to remember the resistor colour code by using short, easily remembered sentences in the form of expressions, rhymes, and phrases, called an acrostic, which have a separate word in the sentence to represent each of the Ten + Two colours.
The resulting mnemonic matches the first letter of each word to each colour which makes up the resistors colour code by order of increasing magnitude and there are many different mnemonic phrases which can be used. However, these sayings are often very crude but never the less effective for remembering the resistor colours. Here are just a few of the more “cleaner” versions but many more exist:
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Bad Boys Ring Our Young Girls But Vicky Goes Without
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Better Be Right Or Your Great Big Venture Goes Wrong
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Buster Brown Races Our Young Girls But Vicky Generally Wins (This one indicates the position of Brown
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Bad Booze Rots Our Young Guts But Vodka Goes Well (in) Silver Goblets (This one includes the tolerance bands of Gold, Silver)
As an added bonus, why not download and make our handy DIY Resistor Colour Code Wheel as a free and handy reference guide to help work out those resistor colour codes.
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