In electronics the most important passive component that is widely used in many circuits, device, equipment, instruments and machines is a “Resistor”. The resistor is the essential part for any electronic circuit and it is available in many different types.
The resistor can be Surface Mount Technology (SMT) and Through Hole (THT) Technology. These two are the types of mounting technologies with regard to PCB assembly and soldering.
In this article we will discuss about the through hole technology resistors. The through hole resistor is the one that has two metallic legs that can pass through the PCB or Vero board. These metallic leads are easily bendable and one can bend it to 90O to make it pass through the Vero board or PCB holes.
How to Find Resistor Value:
The value of resistor is measured in ohms Ω. You can measure the value of a resistor simply by analog or digital multi-meter. But what if you do not have a multi-meter and want to know what the value of particular resistor is.
In this case, you see different color bands on the resistor body. These color bands are the system of specifying the value of resistor.
There are basically 3 major types of resistor coloring schemes. First is the 4 strip / band resistor, second is 5 strip / band and third is 6 strip / band resistor.
4- Strip / Band Resistor:
In this type of resistor, you see that there are total 4 bands of colors. The first band shows the first significant digit. The second band shows the second significant digit, third band is the multiplier and fourth band is the tolerance level.
Following table shows the equivalent numbers for each color band
Resistor Significant Digit Color Schemes for Resistance Value: (Table-1)
When calculating the value of resistor, we read the first band according to above table and write the corresponding number of that band. In this case 1KΩ resistor has the first band = “Brown” whose value is 1. The second band has color black whose value is 0. The third band is color red whose value is 2. Now the third band is the multiplier of 10 raise to the power.
Hence the value of resistor will be
Reading backwards from Value to the Color Band:
Now here if we know the resistor value and want to find the color bands, we again refer to above table and find the corresponding band colors for the numbers given as shown above.
5- Strip / Band Resistor:
Now we will discuss 5 strip/ band resistor.
In the 5 band resistor, the first is the significant digit, second is the significant digit, third is also the significant digit but more commonly known for “accuracy” digit and fourth is multiplier and fifth is tolerance band. The additional 3rd band is introduced to make the resistor accurate to 2 decimal places.
The above table-1 is also applicable for this 5 band resistor. This type of resistor is accurate up-to two decimal places.
We can see that the accuracy is 2 decimal places.
Resistor Multiplier Digit Color Schemes for Resistance Value: (Table-2)
6- Strip / Band Resistor:
In this type of resistor we have total 6 bands. First band is significant digit, second is significant, third is significant and accuracy digit, fourth is multiplier, fifth is tolerance and sixth band is for temperature coefficient. This sixth band shows the dependency of resistor upon environment temperature. It shows how much the change in resistance value of resistor occurs as the change in ambient temperature is observed. Refer to table-3 to check different color bands for corresponding temperature coefficient of resistor. Here ppm/OC means parts per million per degree Celsius. Plus and minus (+/-) sign means the resistance value can deviate above (+) or below (-) its rated value.
In older 5 band resistor type, we see that the 4th band is used for tolerance and 5th band for temperature coefficient. So do not get confused for this. First and second bands are significant and third is multiplier and fourth and fifth are tolerance and temperature coefficient respectively.
Commonly used temperature coefficient band is “Brown”. It means that for a change of 10°C in temperature the resistance value is changed by 0.1%.
Commonly used band for tolerance is gold or silver. The gold band means 5% tolerance while silver means 10% tolerance. In many resistor packaging, you see that the gold band is not actually the metal gold but it is “yellow” color and silver is not actual silver but the “grey” color. This is done to protect the silver / gold metals particles to interfere in high voltage resistors exterior coating.
Resistor Temperature Coefficient Color Schemes for Resistance Value: (Table-3)
Zero Ohm Resistor:
We have also commonly observed in many circuits a special resistor having only single black color band. That resistor is called “Zero-Ohm Resistor”. This is typically used to connected wire or to short traces on the PCBs. This usually serves as a “jumper” on PCB.
Common Rules to Remember:
- Always hold the resistor in your hand such that the metal gold / silver band is on your right
- Always read the resistance bands from left to right
- Memorize the color bands (Black (0) to White (9)), tolerance of gold (5%) and silver (10%) and temperature coefficient of color brown (100 ppm/K) that is commonly used.
- Create some mnemonic for color bands like BBROY Great Britain Very Great W
The amount of power that is dissipated by resistor is known as its wattage. It means that the capability of a resistor to carry high currents. There are 1/8 watt, ¼ watt, ½ watt, 1 watt, 5 watt and 10 watt resistor commercially available in general electronic shops. As the resistor wattage increases hence it increases its capability to pass higher current and accordingly increase its physical size.
The color schemes and resistance value evaluation studied above are for resistors ½ watt, ¼ watt and 1/8 watt. Bigger resistors have different method and usually resistance value is printed on the body of bigger resistors