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Electronics for dummies - McComb G.

McComb G., Boes E. Electronics for dummies - Wiley publishing, 2005. - 433 p.
ISBN: 0-7645-7660-7
Download (direct link): electronicsfordummies2005.pdf
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Figure 16-1:
Logic pulsers feed a short signal burst into a circuit.
Most pulsers get their power from the circuit that youíre testing. You need to remember this fact because, with digital circuits, you generally donít want to present an input signal to a device thatís greater than the supply voltage for the device. In other words, if a chip is powered by five volts, and you give it a 12-volt pulse, you ruin the chip.
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Chapter 16: Ten (Or So) Cool Electronics Testing Tool Tips 363
Be sure that you donít pulse a line that has an output but no input. Some integrated circuits are sensitive to unloaded pulses at their output stages, and you can destroy the chip by applying the pulse improperly. (An unloaded pulse means that the current from the pulse has no way to safely drain to another part of the circuit. If the current is applied to an output of an integrated circuit, for example, that output could be damaged because it is exposed to current itís not meant to take.)
Some circuits work with split (+, -, and ground) power supplies, so make sure that you connect the leads of the pulser to the correct power points to avoid damage to the components.
Counting Up Those Megahertz
A frequency counter (or frequency meter) tests the frequency of a signal. You use a frequency counter to verify that a circuit is operating correctly. For example, suppose you create an infrared transmitter and the light from the transmitter is supposed to pulse at 40,000 cycles per second (40 kHz). With a frequency counter connected to the circuit, you can verify that the circuit is indeed producing pulses at 40 kHz, not 32 kHz, 110 kHz, or some other Hz.
You can use most models, such as the one in Figure 16-2, on digital, analog, and most RF circuits (radio transmitters and receivers are typical RF [radio frequency] circuits). For most hobby work, you need only a basic frequency counter; a $100 or $150 model should do just fine. And, some of the newer multimeters also have a rudimentary frequency counting feature.
Figure 16-2:
A digital frequency counter adds up frequencies.
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364 Part VI: The Part of Tens
In a digital circuit, signals are limited to a range of zero up to about 12 volts. Voltages can vary widely in an analog circuit. Most frequency counters are designed to work with analog voltages ranging from a few hundred millivolts to 12 or more volts. Check the manual that came with your frequency counter for specifics.
Frequency counters display the frequency signal from 0 (zero) Hertz (cycles per second), to a maximum limit that is based on the design of the counter. This limit usually goes well into the megahertz; itís not uncommon to find an upper limit of 25 to 50 MHz. Higher-priced frequency counter models come with a prescaler or offer one as an option. A prescaler is a device that extends the useful operating frequency of the frequency counter to much higher limits. Go for the prescaler feature if youíre working with high frequency radio gear or computers.
A Power Supply with a Changeable Personality
You use a power supply to replace batteries while building and testing circuits at your workbench. A variable power supply provides a well-regulated voltage output, generally ranging from 0 to 20 volts. The model in Figure 16-3 offers a variable output range of about 2 to 20 volts, as well as preset outputs of -5, +5, and +12 volts.
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Chapter 16: Ten (Or So) Cool Electronics Testing Tool Tips 365
In addition to the voltage output of a power supply, pay attention to the current capacity. The higher the current rating of the supply, the more stuff it can power. Avoid a power supply with only a modest current output ó say, less than one amp. You canít adequately drive all circuits with lower currents. Consider a power supply that delivers a minimum of two amps at +5 volts and at least one amp at any other voltage.
Making All Kinds of Signals
A function generator creates nearly pure signal waveforms for testing and calibration purposes. These gizmos are handy when you need to provide a known signal from one circuit to another circuit youíre working on. For example, itís not uncommon to build circuits in stages, one piece at a time. Maybe youíre building a little transmitter and receiver that work using just light, rather than radio frequency waves. You start with the receiver portion. The function generator can temporarily serve as your transmitter. When you get the receiver done, you can build the transmitter, knowing, thanks to the function generator, that the receiver is working properly.
Most function generators develop three kinds of waveforms: sine, triangle, and square. You can adjust the frequency of the waveforms from a low of 1 Hz to a high of between 20 and 50 kHz.
You need a frequency counter to accurately time a waveform. Some function generators come with a frequency counter built-in. If you have a stand-alone frequency counter, you can use it to fine-tune the output of the function generator.
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