ELECTRONIC TEST EQUIPMENT
OSCILLOSCOPE TYPES
The oscilloscope (“scope” for short) is an important
and expensive piece of test equipment. Its main
function is to draw a graph of changing voltages.
The time scale goes from left to right on the graph,
and the voltage (as measured on the probe tip)
goes up and down. The time and voltage scales are
adjustable to accommodate slow, fast, small, and
large signals. Because audio signals, video signals,
and digital logic are all represented by changes in
voltage over time, the scope can suss out most
interesting circuits.
Analog oscilloscopes, the older and less expensive type, show the signal in real time: if a signal
is there, you can put it on the display. You set an
analog scope to trigger when specified voltages are
detected, or when an external device gives the signal.
These scopes work fine for audio signals, but are
much harder to use with digital signals, so don’t
spend your money on an analog scope if you’ll mainly
be working on microcontrollers or USB or other
digital circuits.
A digital oscilloscope adds to these capabilities by
converting digital signals into a signal “trace,” storing
it in memory so you can inspect it. You can also export
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the trace to a computer. Most digital scopes also
have an “autoscale” button that does some of the
knob twisting for you. For more money, you can look
at very long traces, and do frequency analysis
(fast Fourier transform) right on the oscilloscope
itself. Most important, you can look at one-time
events: bursts of data, infrequent signals, or, with
a high-end scope, even specific commands or
address references.
BUYING AN OSCILLOSCOPE
You’ll find hundreds of used analog scopes for $50
and up on eBay. The cheapest ones will need to be
fixed, which is very difficult without a working scope.
Look for the brands Tektronix, HP, Agilent, Hitachi,
Hameg, and Leader. If probes aren’t included, find
them in a separate auction. A new analog scope will
cost $250+, and Amazon carries 4 models.
For digital scopes, a new entry-level model will
cost $1,000 and up; you may be able to find one
used. High-end digital scopes go for $5,000 and up.
Designers of digital scopes do their best to emulate
analog “feel,” so learning on an analog scope is still
relevant, and the entry price is much lower.
Look for a scope with at least 2 channels —
BEFORE THE TEST: The oscilloscope is your window into almost any circuit.
We used ours to discover iPod audio distortion, then clean up the sound.
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