Ten (Or So) Cool Electronics Testing Tool Tips
Okay, so you’re ready to graduate to the electronics big time. But you can’t do it alone. You need a laboratory full of impressive-looking gear with blinky lights, bright knobs, and spinning dials. You’re ready to go out and acquire some of the neat specialized test equipment described below.
You don’t absolutely, positively need these tools just to play around with some LEDs and resistors. A basic multimeter, and maybe a logic probe, are all you need for that. Consider additional test gear after you’ve gained some experience in electronics and want to graduate to bigger and better projects. Unless you’re independently wealthy, just purchase test equipment as you need it.
Put a pulse here, put a pulse there
The logic pulser is a handy troubleshooting accessory for when you work with digital circuits. This handheld tool puts out a timed high or low digital pulse, letting you see the effect of the pulse on your digital circuit. (A pulse is simply a signal that alternates between high and low very rapidly.) Such a pulse might be used to trigger some portion of a circuit that is not otherwise working, for example — you can think of it as a way to “jump start” a cranky circuit. You can switch the pulser between one pulse and continuous pulsing. Normally, you’d use the pulser with a logic probe or an oscilloscope.
Most pulsers get their power from the circuit that you’re testing. You need to remember this fact because, with digital circuits, you generally don’t want to present an input signal to a device that’s 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.
Be sure that you don’t 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 it’s 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 that 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 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.
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; it’s not uncommon to find an upper limit of 25 to 50 MHz. Higher-priced frequency counter models come with or offer a prescaler 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 you’re 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.
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 — say, less than one amp. You can’t 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.
Calling all alien worlds
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 would be bad for something like a radio receiver, which needs to operate over a range of frequencies. By producing a range via 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 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!
Here are the three tools:
- Spectrum analyzer:This tool lets you actually see radio waves. Well, to be precise, you don’t see the waves, but you see the radio energy created by them. The energy appears as a “spike” 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 in a similar fashion as the continuity test you’d 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 don’t mix!