Resistor color code and Variable Resistor

Resistor Color Code

Let’s further move on to learn some more details of resistor. We can see some color rings on the body of resistor, what that mean? Since the size of resistor is very small, writing there value on body is not feasible and even if we write somehow, it will be difficult to read. So these color rings are used to denote the value of resistor with its tolerance range. Each color has specific value mapped with it and each ring position has specific meaning. In market you may get resistance with three, four and five rings, but most common is four rings. So, we will learn here how to read resistor value with four and five color rings or bands. Resistance colour code is quite easy to read once we remember the color values which is explained here.

Value of each color band is mapped as shown in picture. Black is for '0', brown for '1' and so on. To memorize this color band values there are many tips, but I remember the way my hobby teacher taught me in my school days. It goes like this...B B ROY of Great Britain has a Very Good Wife. Follow the capital letters Black (0), Brown (1), Red (2), Orange (3), Yellow (4), Green (5), Brown (6), Violet (7), Grey (8), White (9) or remember the resistance color code like this "bbroygbvgw".

So, the first three or first four bands from one side get the value from this color code and the last band on other side can have two colors, Gold - 5%, Silver - 10% and if no band present it is taken as 20%. This tolerance value indicates that there can be a variation in the value of resistor which can vary from ±5 to 20%. Now let us see how to calculate the value based on band color. In case of four band resistor, first two bands denote a number, third digit is multiplier and fourth one is tolerance. For five band resistor, first three bands denote a number, fourth band denote multiplier and fifth denotes tolerance.

For example, if we have Brown, Black, Yellow and Gold bands on a resistor with four bands resistor, its value is 1 0 × 10 000 = 100,000 Ohms i.e. 100 K Ohms with tolerance 5%. So, it value can be anything between 95 to 105 K Ohms.

Next, if we have five bands on resistor with band colors as Brown, Black, Black, Orange and Gold. Here the value will be 1 0 0 x 1000 = 100,000 Ohms i.e. 100 K Ohms with ± 5% tolerance i.e. 95 K to 105 K Ohms.

So, this is how we can read the value of resistors.

Let's have some more examples here for common resistance values.

• 100 ohm resistor color code: Brown, Black, Brown & the last tolerance color
• 220 ohm resistor color code: Red, Red, Brown & the last tolerance color
• 330 ohm resistor color code: Orange, Orange, Brown & the last tolerance color
• 1K resistor color code: Brown, Black, Red & the last tolerance color
• 4.7K resistor color code: Yellow, Violet, Red & the last tolerance color
• 10K resistor color code: Brown, Black, Orange & the last tolerance color
• 100K resistor color code: Brown, Black, Yellow & the last tolerance color

Based on requirement in the circuit, value of resistance is calculated and nearest value is selected, as all calculated value may not be manufactured. Click here to see how resistance value can be calculated to light a LED with available battery/DC source.

Variable Resistor

So far what we have learnt is about resistor and how to read its value. Now, at some places we need to connect variable resistor also. In some places these variable resistors are inside the device where user cannot change the value of resistor and at some places it is outside system which can be changed by users, a common example is volume control of our music system. When we turn the volume controller we are changing the resistor of a variable resistor. These are usually called "Potentiometer" also, and the other type of variable resistor is called “Preset” which is used inside on the circuit board and is set at one 

position during manufacturing of product and is never changed. These are mostly used where we need to do 

some settings or we are not able to get resistor in market which is actually required to put in circuit, resistors come in some standard values, not all values are manufactured. 

Variable resistors have three terminals, one common and two extreme points as shown in diagram. Terminal B in center is common, A and C are extreme points. When we rotate the shaft in one direction resistance between common and one terminal decreases and at same time it increases between common and other terminal. Similarly reverse happens when rotated in other direction.

This is the symbol of a preset. The value of variable resistors or presets are mentioned on their body as they have sufficient space as opposite to simple resistor which have small cylindrical body and limited space to print their value. That is why the colored rings are made on resistors and standard color code is followed across globe. 

Bigger variable resistors or presets will have their value directly printed like 10K, 100K, 4K7 (4.7K) and 3K3 (3.3K) etc. But smaller presets will have their values mentioned in code format also. Like 102, 403, 220 etc. 

Here the first two digits should be written as it is and replace third digit is the multiplier with 10 to the power third digit (10^3rd digit) and that is the value of preset in Ohms.. For example:

• 102 shall be written as 1 0 X 10^2 i.e. 10 X 100 = 1000 Ohms or 1 KOhms
• 403 shall be written as 4 0 X 10^3 i.e. 40 X 1000 = 40,000 Ohms or 40 KOhms
• 220 shall be written as 2 2 X 10^0 i.e. 22 X 1 = 22 Ohms
• 223 shall be written as 2 2 X 10^3 i.e. 22 X 1000 = 22,000 Ohms or 22 KOhms

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