Experiment 4: Varying the Voltage

Chapter Experiment 4: Varying the Voltage

Make Electronics Book Learning by Discovery
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Make Electronics Book Learning by Discovery

  • Experiment 4: Varying the VoltageChapter 118Experiment 4: Varying the VoltagePotentiometers come in various shapes and sizes, but they all do the same thing: they allow you to vary voltage and current by varying resistance. This experiment will enable you to learn more about voltage, amperage, and the relationship between them. You’ll also learn how to read a manufacturer’s data sheet.You will need the same batteries, battery carrier, alligator clips, and LED from the last experiment, plus:• Potentiometer, 2KΩ linear. Quantity: 2. (See Figure 1-46.) Full-sized poten-tiometers that look like this are becoming less common, as miniature ver-sions are taking their place. I’d like you to use a large one, though, because it’s so much easier to work with.• One extra LED.• Multimeter.LookInsideYourPotentiometerThe first thing I want you to do is find out how a potentiometer works. This means you’ll have to open it, which is why your shopping list required you to buy two of them, in case you can’t put the first one back together again. Most potentiometers are held together with little metal tabs. You should be able to grab hold of the tabs with your wire cutters or pliers, and bend them up and outward. If you do this, the potentiometer should open up as shown in Figures 1-47 and 1-48. Figure 1-46Figure 1-47Figure 1-48. To open the potentiometer, first pry up the four little metal tabs around the edge (you can see one sticking out at the left and another one sticking out at the right in Figure 1-47). Inside is a coil of wire around a flat plastic band, and a pair of springy contacts (the wiper), which conduct electricity to or from any point in the coil when you turn the shaft.Depending whether you have a really cheap potentiometer or a slightly more high-class version, you may find a circular track of conductive plastic or a loop of coiled wire. Either way, the principle is the same. The wire or the plastic