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384 COMMON ELECTRONIC COMPONENTS FOR ROBOTICS

The ohm value of resistors can vary from very low to very high. To make it easier to notate
higher resistance values, resistors employ a common shorthand.
• The letter k (or K) is used to denote 1000. So a resistor with a value of 5 k is the same
as 5000 . Sometimes the symbol is dropped, because it’s understood. So you may also
see the resistor noted with just 5k.
• The letter M is used to denote one million, 1,000,000. A resistor with a value of 2 M has
a value of two million (2,000,000) ohms, or 2 megohms for short.
• Resistor notations for decimal values can vary depending on the country of origin. In the
United States, a 4.7 ohm resistor is notated simply as 4.7 . But some countries, like the
United Kingdom and Australia, often use a different system, where the letter R replaces
the decimal point, as in 4R7. Similarly, a 4.7 k resistor is shown as 4k7.

Resistors are also rated by their wattage. The wattage of a resistor indicates the amount of
power it can safely pass through its body without burning up— the correct term for this is
power dissipation. Resistors used in high- load, high- current applications, like motor control,
require higher wattages than those used in low- current applications. The majority of resistors
you’ll use for hobby electronics will be rated at 1/4 or even 1/8 of a watt.

TESTING THE VALUE OF A RESISTOR
You can readily test the value of any resistor, as shown in Figure 31- 4.

1. Dial the multimeter to read ohms. If your meter is not autoranging, select a maximum
range just above the marked value of the resistor. (If you don’t know the value, select a
high- resistance range to start.)
2. Connect the black ( or COM) lead to one end of the resistor; connect the red lead to
the other end.
3. Read the result on the multimeter. If not using an autoranging meter, try a lower- resistance
range to improve the accuracy of the measurement. If the meter shows over range
(Over range indication, or the meter flashes 1.---) go back up one range.

COMMON APPLICATIONS FOR RESISTORS
Of the myriad uses of resistors in electronic circuits, two stand out as among the most com-
mon. We’ll concentrate on those.

Figure 31- 4 How to check the value
of a resistor using a multimeter. Dial the
meter to read ohms, and, if the meter is not
autoranging, select a range just higher than
the expected resistance value.

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