Intro: Reading Surface Mount Resistor Codes
Unlike Through hole resisors which use colored bands to determine the value, surface mount resistor have numbers and sometimes letters. I will teach you how to take those letters and digits and determine the value.
Looking at the image you see 4 resistors, the first being 391 the seconed 270 and the two at the bottom are the same 30R9. That does not stand for a 391 ohm , 270 ohm, and so on. The formula for breaking the code down is as follows.
1st value-2nd value-multiplier
3 9 1 = 390 ohm resistor
2 7 0 = 27 ohm resistor
2 3 3 = 23000 ohm or 23K ohm resistor
There are some resistors which have 4 digits. The formula is the same with the addition to a digit.
1st value-2nd value-third value-multiplier
2 3 5 3 = 235K ohm resistor
You may ask"why some have three diigits and some have four?" three digits typically means that the resistor is 5% tolerance the four digit typically means the resistor is 1% tolerance. If a letter is used to represent tolerance use the chart below.
Now you will notice that the last two resistor have an "R" in the equation. The way to look at these is very simple. The R represents a decimal. So 30R9 is a 30.9Ohm resistor.
R23= .23 ohm
5R6= 5.6 ohm
45R3= 45.3 ohm
Of course you can read the values with a meter, but whats the fun in that? I hope you all learned something from this little write up.