Page 38 - Troubleshooting Analog Circuits

Choosing the Right Equipment 25

m ANALOG OR
m ANALOG OR
DIGITAL
DIGITAL
VOLTMETER
VOLTMETER
10 mV/% Lo
Figure 2. I I. The LM35CAZ is a good, simple, convenient general-purpose temperature sensor. But be-
ware of using it to measure the temperature of very small objects or in the case of extreme
temperature gradients; it would then give you less accurate readings than a tiny thermo-
couple with small wires.

27. Little filters in neat metal boxes, to facilitate getting a good signal-to-noise ratio when
you want to feed a signal to a scope. They should be set up with switch-selectable
cut-off frequencies, and neat connectors. If in your business you need sharp roll-offs,
well, you can roll your own. Maybe even with op-amps and batteries. You figure out
what you need. Usually I just need a couple simple Rs and Cs, with an alligator clip
to select the right ones.

28. Line adapters-those 3-wire-to-2-wire adapters for your 3-prong power cords. You
need several of them. You only need them because too many scopes and function
generators have their ground tied to the line-cord’s neutral. You need some of these
to avoid ground-loops. You also need a few spares because your buddies will steal
yours. For that matter, keep a few spare cube taps. When they rewired our benches a
few years ago, the electricians tried to give us five outlets per bench. I stamped my
feet and insisted on ten per bench, and that’s just barely enough, most of the time.

You’ve come to the end of my list of essential equipment for ordinary analog-
circuit troubleshooting. Depending on your circuit, you may not need all these items;
and, of course, the list did not include a multitude of other equipment that you may
find useful. Logic analyzers, impedance analyzers, spectrum analyzers, program-
mable current pumps, capacitance meters and testers, and pulse generators can all
ease various troubleshooting tasks.
Each of you will have your own idea of what is essential and what is unnecessary
for your special case, and I would be delighted to get feedback on this subject. You
can write to me at the address in the Acknowledgments section of this book.

References

1. Collins, Jack, and David White, “Time-domain analysis of aliasing helps to alleviate DSO
errors,’’ EDN, September 15, 1988, p. 207.