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A sweep generator is a type of function generator, but with a cool twist. A sweep generator produces signals that are somewhat different from the ones that a standard generator puts out, in that it sweeps the frequencies up and down. Not only does this sweep sound like E.T. calling home (connect a speaker to the output of the sweep generator to hear this effect), but it also helps you find frequency-sensitive problems in your circuits.
So what is this frequency-sensitive thing? Frequency-sensitive means that a circuit is sensitive to specific frequencies. Because of that characteristic, a circuit may function perfectly well at one frequency, but not at another. This
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366 Part VI: The Part of Tens
would be bad for something like a radio receiver, which needs to operate over a range of frequencies. If you produce a range by sweeping the frequencies, you can more quickly see if your circuit is operating under all the conditions that you want it to.
A sweep generator varies the frequency of the output waveform, typically within pre-selected limits, such as 100 Hz to 1 kHz or 1 kHz to 20 kHz. You most often use sweep generators in troubleshooting audio and video equipment, where altering the frequency reveals bad components.
Some function generators also have a sweep feature, covering two functions with one tool.
A logic analyzer is like a souped-up oscilloscope (you can read about oscilloscopes in Chapter 10). It shows you the waveforms of several inputs or outputs of a digital circuit at the same time. You most often use a logic analyzer to test digital gadgets, and those folks well versed in the black arts of electronics find this analyzer useful.
One way you can use a logic analyzer is to check clock and data signals for a microcontroller. These devices require very specific timing relationships for various signals that you feed into them simultaneously. The logic analyzer lets you freeze-frame all the signals. Then you can see if a signal is missing or doesnít sync up with the others, as it should.
If you think that youíre ready to try a logic analyzer, you can buy a stand-alone model or one that connects to your PC. Stand-alone units cost a pretty penny, and theyíre very sophisticated. Consider getting a less expensive logic analyzer adapter for your PC. These adapters connect to the USB, serial, or parallel ports of your computer. You need special software that comes with the adapter. Most PC-based logic analyzers handle between 8 and 16 digital inputs at one time.
A Trio of Testing Toys
Here are three testing tools that are somewhat specialized, but if you know a bit about them, you can impress people in electronics discussion forums. Oh, and you may just need one or more of them in a project someday!
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Chapter 16: Ten (Or So) Cool Electronics Testing Tool Tips 367
Here are the three tools:
Spectrum analyzer: This tool lets you actually see radio waves. Well, to be precise, you donít see the waves, but you see the radio energy created by them. The energy appears as a ďspikeĒ on an oscilloscope-like display. People sometimes use spectrum analyzers in amateur radio work to determine if a transmitter is on the fritz.
Signal injector: This one literally injects a signal into an analog circuit. You use one of these puppies to test whether radios and televisions are in working order. You listen for the signal using a signal tracer or meter. You use the signal injector and tracer like youíd use the continuity test you perform with a multimeter, but this test goes further. To the trained ear (yes, these gadgets take some skill to use properly), you can tell just by the tone if components in the circuit may be bad.
Static meter: If you have read much of this book at all, you know that static electricity can cause all kinds of problems for electronics components. You can use a static meter to scope out dangerous levels of static electricity on or near your workbench. If you get high readings, you can take steps to minimize the static. Remember that sensitive electronic components and static donít mix! Be sure to check out Chapter 2 for additional tips on reducing static electricity.
Where to Get Testing Tool Deals
I wonít kid you ó electronics test equipment can cost you a lot of money. Much of what you pay for is the accuracy of the device. Manufacturers of this or that doodad strive for high accuracy to tout their product in the market or meet necessary government regulations. If youíre an electronics hobbyist working at home, you donít really need a very high level of accuracy. Usually you can get by with less expensive models.
When you buy any test gear, especially the special-purpose stuff mentioned in this chapter, donít automatically go for the high-priced spread. A pricey doohickey canít make you a better electronics tech. The low-end model is likely to be good enough for most hobby applications, and assuming that you take good care of it, it should last many years.