From the course: Electronics Foundations: Basic Circuits

Read resistor color codes

From the course: Electronics Foundations: Basic Circuits

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Read resistor color codes

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- [Instructor] Rather than directly printing the resistance values of resistors on the component, most resistors use some form of coded markings to indicate their resistance value. Surface mount resistors use a coded sequence of three or four letters and numbers printed on the top of the little rectangular case to indicate their resistance value. Plated through-hole resistors, which I'll be looking at in this video, use a sequence of colored bands to indicate their resistance. The most common resistors you'll see use four colored bands. The colors of the first two bands indicate a two-digit value for the resistance, which is then multiplied by a power of 10, indicated by the third color. The fourth band indicates the manufactured tolerance of the resistor and will almost always be either gold or silver colored. So to figure out which end of the resistor has the first band, just look for the gold or silver-colored tolerance band, which is last, and you'll know to start reading the colors from the other side. Also, if you look closely, you can see that the gap between the tolerance band and the multiplier band is slightly wider than the gaps between the other colored bands. You can decode the resistor's value from the first three bands using a table like this one, which I've included in the exercise files. The first band of the resistor shown here is brown and the second band is black. Those colors correspond to the numbers one and zero in the digit value column, so we'll write those down. Next, I'll determine the multiplier by looking at the third band, which in this case is red, and that corresponds to a multiplier of 10 to the power of two. 10 times 10 to the power of two is 1,000 ohms or one kiloohm. For the fourth band, The color gold represents a resistor tolerance of plus or minus 5% and the color silver is a tolerance of plus or minus 10%. This 1,000 ohm example resistor has a gold band, so its actual resistance should be somewhere between 950 ohms and 1,050 ohms. If you find the color decoding process a bit confusing, or if you're feeling lazy, like I usually am, there are plenty of online tools that will do the decoding for you. For example, this resistor calculator on hobby-hour.com allows you to specify the resistor value you want. I'll enter 1,000 ohms and then it will display a picture of the resistor you should look for. Or if you already have a resistor and you just want to know its value, you can select the colored bands for it on the right and the website will calculate the resistance value for you. Now, notice that this website allows you to select either four or five-colored bands. That's because in addition to the common four-band resistors, there were also resistors that use a five-band scheme. They're usually high-precision resistors and that additional color band gives you an extra digit of precision for the resistance value. Fortunately, the process for reading five-band resistors is basically the same as resistors with four bands. When reading a five-band resistor, the first three bands indicate the digits for the resistance value. The fourth band is the multiplier and the fifth band indicates the tolerance. Now, unlike four-band resistors that usually have a tolerance of plus or minus 5 or 10%, which is indicated by gold or silver, resistors with five bands are manufactured to be more precise and have a tolerance of 2% or less. Therefore, rather than using gold or silver for the tolerance band, resistors with five bands typically use brown, red, green, blue, or violet to indicate the tolerance values shown here. Since these are the same colors that are used for the other four bands of the resistor, to identify which band is the tolerance band, look for the wider gap, which will be between the tolerance and multiplier bands. As an example, the first three bands of the resistor shown here correspond to the numbers three, one, and six. The fourth band indicates a multiplier of 10 to the power of two, and the fifth band, which is brown, means it has a tolerance of plus or minus 1%. So this is a 31.6 kiloohm resistor plus or minus 1%. In general, I recommend stocking your part kit with four-band resistors that have a tolerance of 5%. That tolerance is good enough for most hobbyist projects and they'll be much cheaper than the higher-precision five-band resistors. If you do decide that you need the extra precision for your projects, now you know that those resistors exist and how to read them.

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