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You know those late-night commercials that try to sell you those amazing kitchen gadgets that are like a combination blender, juicer, food processor, mixer, and snow cone maker all in one? A multimeter is kind of like one of those crazy kitchen gadgets, except that, unlike the crazy kitchen gadgets, a multimeter really can do all the things it claims it can do. And, unlike the crazy kitchen gadgets, the things a multimeter can do turn out to be genuinely useful.

Along with a good soldering iron, a good multimeter is the most important item in your toolbox. Learn how to use it, and your electronic exploits will be much more fruitful.

Figure 8-1 shows a simple, inexpensive multimeter. This one can be purchased from almost any hardware store for under $20. If you shop around, however, you can often find a basic multimeter for under $10 and sometimes for as little as $5.

FIGURE 8-1: You can buy a basic multimeter like this one for under $20.

Of course, you can also spend much more, but if you’re just getting started, an inexpensive multimeter is fine. Eventually, you’ll want to invest a little more money in a better-quality multimeter.

The multimeter shown in Figure 8-1 is a digital multimeter, which displays its values using a digital display that shows the actual numbers for the measurements being taken. The alternative to a digital multimeter is an analog multimeter, which shows its readings by moving a needle across a printed scale. To determine the value of a measurement, you simply read the scale behind the needle.

Figure 8-2 shows a typical analog multimeter. This one happens to be one of my favorites. Even though it’s old enough to be called vintage, it’s still an excellent and accurate meter. One of the benefits of spending a little more to buy quality equipment is that the equipment will give you many years — sometimes decades — of reliable service.

FIGURE 8-2: An analog multimeter.

For the most precise measurements, you can pick up a lab-quality bench-top multimeter such as the one shown in Figure 8-3. These meters usually cost $100 or more but offer additional features such as data logging, USB or network connectivity, and a wide array of test leads useful for different circumstances.

The following paragraphs describe the various parts that make up a typical multimeter:

 Display or meter: Indicates the value of the measurement being taken. In a digital multimeter, the display is a number that indicates the amperage (current), voltage, or resistance being measured. In an analog meter, the current, voltage, or resistance is indicated by a needle that moves across a printed scale. To read the value, you look straight down at the needle and read the scale printed behind it.FIGURE 8-3: A bench-top multimeter.

 Selector: Most multimeters — digital or analog — have a dial that you can turn to tell the meter what you want to measure. The various settings on this dial indicate not only the type of measurement you want to make (voltage, current, or resistance) but also the range of the expected measurements. The range is indicated by the maximum amount of voltage, current, or resistance that can be measured. Higher ranges let you measure higher values but with less precision. For example, the analog multimeter shown in Figure 8-2 has the following ranges for reading DC voltage: 2.5 V, 10 V, 50 V, 250 V, and 500 V. If you use the 2.5 V range, you can easily tell differences of a tenth of a volt, such as the difference between 1.6 and 1.7 V. But when the range is set to the 500 V range, you’ll be lucky to pick out differences of 10 volts.

 On/off switch: Some multimeters don’t have an on/off switch. Instead, one of the positions on the selector dial is Off. Other multimeters have a separate on/off switch. If your meter doesn’t give you any readings, check to make sure the power switch is turned on or that the battery doesn’t need to be replaced.

 Test leads: The test leads are a pair of red and black wires with metal probes on their ends. One end of these wires plugs into the meter. You use the other end to connect to the circuits you want to measure. The red lead is positive; the black lead is negative.