Get the most from your oscilloscope: part 1

Oscilloscope technology has evolved from electromechanical assistance for hand-plotting to the development of full-featured automated digital instruments.

The oscilloscope is an invaluable instrument that provides engineers with a picture of how signals inside their circuits behave. Today, they have evolved from analog versions, where the only option for long-term storage was to take a Polaroid picture of a displayed waveform, to digital models that can effortlessly store data for later recall and post-measurement analysis. The digital versions also have sophisticated triggering capabilities that help you quickly diagnose the most subtle faults, and they can automate many measurement tasks.

Generally, the oscilloscope plots voltage amplitude as a function of time. Efforts to develop such plots extend back to the 19th century,^[1] when the French scientist Jules François Joubert developed an electromechanical system that assisted with the hand-plotting of time-varying galvanometer measurements. Subsequent innovations coupled a pen directly to the galvanometer, enabling the capture of measurement results on a rotating scroll, eliminating the need for hand-plotting.

Figure 1. An oscilloscope’s vertical and horizontal controls have remained similar over the decades. (Image: Drumcliff from Pixabay)

Q: That sounds like a chart recorder, which is still in use today. But when was the oscilloscope, as we now know it, developed?
A: The invention of the cathode-ray tube (CRT) in the late 19th century was one key. And although flat panels have now replaced the CRTs, the flat panels display the same general type of waveform information. Additional developments in the first half of the 20th century, such as the triggered sweep, led to instruments with the basic functionality of today’s oscilloscopes.

Q: I used an oscilloscope in college, but have focused on software development since. Can you provide a review of how to use one?
A: If you went to college a long time ago, you may have used a vacuum-tube scope such as the one my colleague Martin Rowe tore down.^[2] If you attended in the late 20th century, you may have encountered an oscilloscope such as the 10-MHz single-channel analog Model GOS-310 (Figure 1) from Good Will Instrument, a Taiwanese company now known as GW Instek. I’m not sure exactly when this model was in production, but I did find schematic diagrams for it created and approved in the late 1980s. (If you have more information, let me know in the comments.) With the GOS-310, the CRT remains, but transistors take the place of other vacuum tubes.

If you look at Figure 1 on the left, just below the display, you’ll see the vertical controls, which let you set vertical sensitivity in volts or millivolts per division. To the right, you’ll see the horizontal controls, which let you set horizontal sweep times in milliseconds or microseconds per division. Below the horizontal controls, you’ll see the trigger control, about which we will have more to say later.

Q: How does this front panel compare to a more modern oscilloscope?
A: Let’s look at the Keysight InfiniiVision HD3 Series digital scope, a 1-GHz, 14-bit, 4-channel model (Figure 2) introduced in September 2024.

Figure 2. On the Keysight InfiniiVision HD3, pushbuttons enable one knob to control the vertical sensitivity of four channels. (Image: Keysight Technologies)

On the top right, you’ll see the horizontal controls; below that, the trigger controls; and at the bottom right, the vertical controls, with pushbuttons enabling one knob to control all four channels. The Keysight oscilloscope also offers many features, such as markers missing from the older analog instrument, but from a high-level perspective, many of the basic operations remain the same.

Q: So, we can continue counting on seeing the knobs.
A: No, not really. For example, I have a PicoScope, which has no knobs, no screen, no user interface at all. In Figure 3, I have connected the PicoScope to my laptop via USB and have launched the PicoScope software. The software identifies the specific PicoScope model I have and configures the user interface accordingly.

Figure 3. PicoScope software identifies the hardware model and configures the user interface accordingly. (Image: Rick Nelson)

Despite the lack of knobs, you should feel at home with the intuitive interface. At the top left of Figure 3, enlarged in Figure 4, you’ll see the familiar volts-per-division, time-per-division, and trigger controls. Modern oscilloscopes like the Keysight and PicoScope models have many functions that automate tasks and minimize measurement errors. We’ll take a closer look in part 2 with some specific measurement examples.