Getting Started with Arduino

Appendix B. Reading Resistors and Capacitors

In order to use electronic parts, you need to be able to identify them, which can be a difficult task for a beginner. Most of the resistors that you find in a shop have a cylindrical body with two legs sticking out and have strange coloured markings all around them. When the first commercial resistors were made, there was no way to print numbers small enough to fit on their body, so clever engineers decided that they could just represent the values with strips of coloured paint.

Today's beginners have to figure out a way to interpret these signs. The "key" is quite simple: generally, there are four stripes, and each colour represents a number. One of rings is usually gold-coloured; this one represents the precision of that resistor. To read the stripes in order, hold the resistor so the gold (or silver in some cases) stripe is to the right. Then, read the colours and map them to the corresponding numbers. In the following table, you'll find a translation between the colours and their numeric values.

Colour	Value
Black	0
Brown	1
Red	2
Orange	3
Yellow	4
Green	5
Blue	6
Purple	7
Grey	8
White	9
Silver	10%
Gold	5%

For example, brown, black, orange, and gold markings mean 103±5%. Easy, right? Not quite, because there is a twist: the third ring actually represents the number of zeros in the value. Therefore 1 0 3 is actually 1 0 followed by 3 zeros, so the end result is 10,000 ohms ±5%. Electronics geeks tend to shorten ...