Introduction: 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.
B=.1%
C=.25%
D=.5%
F=1%
G=2%
J=5%
K=10%
M=20%
Z=80%
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.
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