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Working with AC Current
The vast majority of hobby electronics projects run on batteries. Simple enough, but some projects need more current or higher voltages than batteries can easily provide. Instead of building a power supply that converts household AC current to a DC voltage for your project, you can make things much safer for yourself by using a wall transformer to convert AC to DC (see Figure 2-2). All the working parts are self-contained in the wall transformer. As long as you donít try to take it apart, you donít expose the AC house current.
Where to get wall transformers ó cheap!
You can purchase wall transformers (called "wall warts" by some because they stick out of the wall like an ugly wart) new or as surplus. Try Radio Shack or a similar electronics store to buy new wall transformers. You can get used and surplus wall transformers by mail-order surplus; check out Chapter 17 for some good leads.
And, of course, you may have a wall transformer saved from a discarded cordless phone or other electronic gadget. Check the voltage and current rating, usually printed on the transformer, to see if it's suitable for your next project.
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Part I: Getting Started in Electronics
A plug-in wall transformer shields you from exposed AC household current.
Sometimes, you need to work on a project that uses your 117 volt AC house current directly. In those cases, you canít resort to relatively safer batteries. No hiding behind a wall transformer either. For these projects, always exercise caution. Although youíre being super careful, you can further minimize the hazards of working with circuits powered by AC house current by following these basic guidelines:
^ Always keep AC circuits covered. A little sheet of plastic works wonders.
^ Never circumvent any fuse protection used on the device. Donít use a fuse with a too-high rating and donít bypass the fuse altogether.
^ When troubleshooting AC circuitry, keep one hand in your pocket at all times. This prevents you from accidentally touching things with your hand that you shouldnít. Use the other hand to manipulate the testing apparatus. Avoid the situation where one hand touches ground and the other a live circuit. The AC can flow from one hand to the other, straight through your heart.
^ If possible, use the buddy system when working with AC circuits.
Always have someone nearby who can help you in case you get a nasty shock.
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Chapter 2: Keeping Humans and Gadgets Safe
Double- and triple-check your work before applying power. If possible, have someone who knows a little about circuits inspect your handiwork before you switch the circuit on for the first time.
^ Periodically inspect AC circuits for worn, broken, or loose wires and components and make any necessary repairs.
When testing AC-operated circuits, first remove the power. Unplug the power cord, donít just switch off the power at an outlet strip. You can easily tell when youíve pulled the plug from the socket, but itís harder to tell if those little electrons are still swirling around the outlet strip.
The Heat Is On: Safe Soldering
When soldering, you use a hot soldering pencil or gun, working with temperatures in excess of 700 degrees Fahrenheit. To get an idea of what that temperature means, itís the same as an electric stove burner set at high heat. You can imagine how much that hurts if you touch it.
Most electronic projects or fix-it jobs call for a soldering pencil rather than those big soldering guns that look like theyíre rejects from a Buck Rogers movie. Chapter 8 discusses soldering in more detail, but for now, keep the following safety tips in mind:
Always place your soldering pencil in a stand designed for the job.
Never place the hot soldering pencil directly on a table or workbench. You can easily start a fire or burn your hands that way.
Be sure that the electrical cord doesnít snag on the table or any other object. Otherwise, the hot soldering pencil can get yanked out of its stand and fall to the ground. Or worse, right into your lap!
Soldering produces mildly caustic and toxic fumes. Make sure that your electronics workshop has good ventilation to prevent a buildup of these fumes. Avoid hunching over the soldering work because the fumes can waft into your face. Yuck. If youíre having trouble seeing the soldering joint at a distance, use a magnifying glass to enlarge the image of the work.
If your soldering pencil has an adjustable temperature control, dial the recommended setting for the kind of solder that youíre using.
If youíre concerned about stunting your growth and other health issues, you may want to avoid solders that have lead in them. As an
alternative, you can use lead-free rosin-core solder specifically designed for use on electronic equipment. Never use silver solder or acid-flux solder in electronics, by the way. They wreck your circuits.