Resistors are fundamental in today’s electronic circuits, since they not only serve as a control element, but also as a protection element. However, they are usually very compact, so manufacturers use a color code to define the value of each one in ohms.
Most of the devices that we use in daily life use resistors, since these electronic components allow proper operation by introducing a certain resistance between two points in a circuit. For example, a small LED light bulb, which typically uses a very low current flow , usually needs a resistor to limit the current flow, otherwise it would burn out instantly. However, resistors vary according to their value in ohms.
Axial Encapsulation Resistor
The most common electronic resistor is the axial encapsulated one, a small cylindrical piece that has a set of colored bands, with which the manufacturers indicate the codes to know the value of each one. Usually it is 3, 4 or 5 stripes . These are read from left to right, where the last one refers to the tolerance, that is, the percentage of precision. In this way, the penultimate band is the multiplier, while the first ones are the significant figures.
Resistors: Meaning of the colored bands
The color codes of the resistors are obtained by converting the bands into a number, but for this we must know how much each tone is worth. Let’s review below the table of resistances used by manufacturers commercially.
It is worth mentioning at this point that the color code for resistors was created in the 1920s, in the North American company Radio Manufacturer’s Association. Currently, IEC 60062 is the international standard, and it is unlikely that any new colors will be added to the table in the near future.
Resistor colors can vary in hue depending on the manufacturer, however, they are generally easy to recognize and the bands are not confused with each other. On the other hand, in some cases special attention must be paid, since serious power failures could damage the color, making it more difficult to know the value of each component. In this sense, it is preferable to use a multimeter to calculate the resistance more accurately, but it is important to remove the piece, removing the solder with the help of a heat gun, since the other elements of the circuit can affect the measurement. In any case, in case of doubt, it is recommended to consult an expert.
How to calculate resistor value using colors?
Measuring a four-line resistor is very easy; the first two are translated with a two-digit integer. Therefore, the first line is for the tens digit, while the second is for the ones digit. For its part, the third line represents the power of 10 by which the number must be multiplied, in other words, it is the number of zeros that we must add. This is how the resistance value expressed in ohms is obtained .
Suppose we have a resistor with the following sequence of colors from left to right:
Green – Gray – Brown – Gold.
For the calculation of resistances, we must take into account the value of the color indicated in the table. In this way, we have to:
Green = 5 Gray = 8 Brown = 1
The last one is the multiplier, in this case, we add a single zero. Therefore, we are dealing with a 580 Ω resistor.
For accuracy, we have a gold band, which has a value of ±5%. Thus, we can make a simple rule of three: 580 x 5/100 = 29 Ω. Then, we just have to subtract and add this margin of error to the value of the resistor, that is, 580 – 29 = 551 and 580 + 29 = 609, which allows us to conclude that the accuracy range of this resistor is between 551 Ω and 609 Ω. This is what we commonly know as tolerance within the commercial values of resistors.
high precision resistors
In special cases, some circuits need higher precision, so the last stripe from left to right may be a different color. Usually green or brown, which means the margin of error is ±2% or ±1% respectively. Likewise, although they are not usually commercial resistances, there are also the following:
Green = ±0.5%, Blue = 0.25%, Violet = 0.1% and Gray = 0.05%
What are SMD resistors?
It is good to mention the surface mount resistors, also called SMD, for its acronym in English. These are widely used on circuit boards, they are usually small and rectangular in shape, making it easier for manufacturers to place the value with a number.
In this case, the resistor color table is not used, since they do not have marked stripes, but simply a three-digit number, where the first number is the most significant, the second is the integer and the last is the quantity. of zeros that we must add. So if the resistor reads 100, the actual value would be 10Ω. In case of having an R, it means that it is precision, so where the letter is, a decimal point goes. For example, if it has the code 2R4 marked, it means that it is 2.4Ω.
Another way to know the value of a resistor
We do not always have time to manually calculate the actual value and tolerance, so it may be a good idea to see the resistance online, using an internet calculator. It is an application in which we only have to enter the order of the colors of the bands to know all the data we need automatically.
Finally, although the multimeter is the instrument that allows you to measure the values of the resistances with greater accuracy, the main advantage of using a resistance calculator is that it speeds up the work considerably. Also, it is a free service.