Robot Building for Beginners, Third Edition

CHAPTER 9 ■ RESISTORS

Measuring Resistance

1. If your meter isn’t already on the 200 range (or thereabouts) for ohms, switch the
   dial now.


2. As always, connect the black lead to the COM terminal of the multimeter.


3. Connect the red lead to terminal marked W or ohm or whatever the specific
   instructions are for measuring resistance on your particular meter.


4. Turn on the meter.

It would be helpful to use alligator-clips or hook adaptors (if you have them) for your meter test probe
tips. It’s somewhat difficult to touch each end of a resistor with both probe tips at the same time without the
resistor rolling away.

5. Find a 100 W resistor. The color bands are brown, black, brown, gold. There’s no
   such resistor as gold, brown, black, brown (backwards). If you think you’ve found
   one, you’re reading in the opposite direction.

In a prior chapter, the color-code table indicates that brown is 1, black is 0, brown is × 10, and gold is 5%
tolerance. That is 100 ± 5 W.

■ Note The symbol ± means plus or minus. In this example, 100 plus 5 is 105 and 100 minus 5 is 95. So,

the value of the resistor could be anything from 95 to 105.

6. Touch or connect the black probe tip to one end wire of the resistor
   (see Figure 9-6). It doesn’t matter which ends you choose.


7. Touch or connect the red probe tip to the other end wire of the resistor.

Interpreting the Resistance Displayed on the Meter

If you’re freakishly lucky, the meter is displaying 100 W. More likely, the meter is showing a number slightly
above or below 100. That’s perfectly normal. (I can’t tell you how many resistors I went through to get that
near to 100 W for the picture in Figure 9-7.)

Figure 9-6. Hook test probe adaptors holding a 100 W resistor