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Adventures in Science: How to Use an Oscilloscope

Staring at the multitude of buttons, switches and knobs on the face of an oscilloscope can be daunting. For this "Adventures in Science," we show you how to take basic measurements with an oscilloscope.

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Last week, we went over bench power supplies, which brings us to another defining tool you might find on an electronics bench: the ever useful oscilloscope!

Oscilloscopes allow you to visualize how electrical signals change over time. This means you can measure periodic and transient signals, which might be too fast for your digital multimeter to catch. Oscilloscopes can be indispensable for debugging circuits.

In the video, I talk about why 10x probes are useful, how to tune the compensation capacitor in a 10x probe, how to measure periodic signals, and how to set up a single capture trigger for a transient signal. I hope that this works as a starting place for someone who might be just beginning with oscilloscopes.

Once again, if you prefer the written word, we have a tutorial to guide you:

How to Use an Oscilloscope

February 25, 2014

How to work the dials and buttons on an oscilloscope, and a glossary of the o-scope lexicon.

I know that I covered just the basics in the video, and there are many, many more features packed into most oscilloscopes. What other tips and tricks might you mention to a beginner?

Comments 4 comments

  • Shawn,

    Although I think you did an excellent job of covering a “modern” DSO, I really think that you’ve done a disservice to your target audience, namely the hobbyist, especially the “beginner” in electronics. They can look at the prices for DSOs, and USB “pods”, and get scared off. Think, for example, of a teenager who’s mowing lawns (or shoveling snow off sidewalks and driveways), and think about how many lawns (or driveways) need to be done to purchase a brand-new ‘scope (or pod). Now think about the “old clunkers” that can be had at the typical ham-fest at a price that can be covered by mowing a single lawn, sometimes with enough left over to buy a burger for lunch! Sure, a lot of these old clunkers are only 5MHz, and you’ll probably have to buy a probe separately (for maybe 4 or 5 times what the 'scope cost – another lawn or two’s work), but you can still learn a LOT from it. (Yeah, if you want to “document” the image, you’ll have to use your smart phone to take a picture…)

    I think you misled folks a bit on bandwidth – the display will still show a sine wave nicely near (or even at) the specified bandwidth, albeit a bit attenuated. The problem comes when you try to examine a differently shaped signal, such as a square wave, where the ‘scope display starts “rounding over” the sharp edges above about 1/5 the bandwidth. (For readers interested in the “why”, look up Fourier Analysis – a topic on which a lot of time is spent by Electrical Engineering students.)

    One other point which doesn’t get a lot of coverage: the maximum input voltage. Many of today’s DSO’s and pods will be “smoke emitters” if they are connected by a 1x probe to the wall socket. (I’ll skip the issue of grounding/isolating the scope for now.)

    • I disagree, but for the following good reasons…

      Analog scopes are frequently found in an unknown (for an amateur), and potentially unknowable, state of repair. Many of the repair manuals of these noble analog workhorses are difficult, if not impossible, to find, and the repairs and calibrations a found scope may require may be well-outside an amateur’s ability to perform. Furthermore, the repair procedure will likely require replacement parts, many of which may be obsolete, and possibly have no suitable modern equivalent.

      Acquiring good tools can be costly; but an analog scope can be a yak-shaving project with no payout, unless you are fortunate enough to have an old salt on-hand to guide you. As a restoration project, it might be fun, but without a complete teardown, repair, and calibration, it is not a tool.

      As digital scopes approach the Nyquist frequency, they do tend to look just like Shawn’s “low poly” pictures; analog scopes do tend to round digital signals in this range, as they struggle to present detail that doesn’t exist; a fact that is present in analog signals at this frequency as well, if you know how to look for this loss of detail.

      I can’t heartily recommend a scope that can’t read an Arduino’s clock, either; which means the required “entry level” is firmly at 100 MHz, and well beyond most analog scopes.

      • I beg to differ, for even better reasons…

        Although I agree that the analog scopes are often in an “unknown state of repair”, given the cost of a lot of the analog o'scopes, often $20 to $40, even if the ‘scope isn’t working, you’re not out much. If you give it two or three tries, you’ll likely find one that is, at least mostly, working. (Today’s “beginners” should NOT be poking around inside an analog oscilloscope as there are thousands of volts on some of the parts. So the lack of manuals and parts become a moot point.)

        Getting state-of-the-art measurement tools IS costly, and, for the professional who has to have the exotic “bells and whistles”, the fancy tools MIGHT be worth the co$t, but for the amateur, especially the beginner, buying a $20,000 test instrument is ABSURD. Yeah, that old analog instrument may not be able to get you the readout and fancy display, but it CAN show you what the waveform looks like.

        In about 45 years of using ‘scopes, I know that most of my “hobbyist” usage has no need of “NIST traceable calibrations”. Sure, as a professional, I have had occasion to use only 'scopes that regularly went in for calibration, but when I’m looking at an Arduino that is only 16 MHz, and I’m wondering if the 800 kHz I2C signal is “clean” (or even “present”), that old clunker 20 MHz 'scope that was last calibrated before Shawn was born is fine. (I can bounce the probe off the Vcc line a few times to get an idea where the 5V and ground are on the screen – I really only need to know within a half-volt or so on the readings.)

        BTW, for the 100 MHz processors, those frequencies are usually only WITHIN the CPU chip – they’re derived by using Phase-Lock Loops (PLLs) that are referenced to an external crystal that is in the 10 MHz to 20 MHz range. All of the other signals take several clocks to generate. This is especially true for people who are using Arduinos as building blocks – they’ll never need to look at the really high-speed stuff, or, at most, do so to check that the board isn’t “dead”, and even if it happens to be at the rated frequency (and so “reads” about 30% low) that’s “good enough” to know whether the board is “alive” or “dead”.

        I say that “entry level” for a ‘scope for the beginner hobbyist is 1/20th what you claim, or 5 MHz, and the last time I saw an old boat-anchor that low at a hamfest (I average about 4 a year) was about 20 years ago, and they were asking $5 for them. They’re plenty for looking at most serial and audio signals, as well as the PWM “psuedo-analog-output” signals. And for a “professional”, 100 MHz may well be a factor of 10 (or more) too LOW, but for the “professional”, someone else is paying for it (and, for high-end stuff, they can be rented or leased).

        • You’re just proving my point. A newbie will never know whether his readings are any good because he won’t be skilled enough to calibrate the scope, and even if he wanted to, he shouldn’t risk it. A modern scope is going to be much less of a hassle, and much easier to keep in-spec.

          An old Analog Scope in an unknown state of repair is no longer a tool; it’s a hobby project. It doesn’t even meet current needs anyway.

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