Everything You Need To Know About Logic Probes

We just spent the last hour watching a video, embedded below, that is the most comprehensive treasure trove of information regarding a subject that we should all know more about — sniffing logic signals. Sure, it’s a long video, but [Joel] of [OpenTechLab] leaves no stone unturned.

At the center of the video is the open-source sigrok logic capture and analyzer. It’s great because it supports a wide variety of dirt cheap hardware platforms, including the Salae logic and its clones. Logic is where it shines, but it’ll even log data from certain scopes, multimeters, power supplies, and more. Not only can sigrok decode raw voltages into bits, but it can interpret the bits as well using protocol decoder plugins written in Python. What this all means is that someday, it will decode everything. For free.

[Joel] knows a thing or two about sigrok because he started the incredibly slick PulseView GUI project for it, but that doesn’t stop him from walking you through the command-line interface, which is really useful for automated data capture and analysis, if that’s your sort of thing. Both are worth knowing.

But it’s actually the hardware details where this video shines. He breaks down all of the logic probes on his bench, points out their design pros and cons, and uses that basis to explain just what kind of performance you can expect for $20 or so. You’ll walk away with an in-depth understanding of the whole toolchain, from grabber probes to GUIs.

Indeed, toward the end, [Joel] simulates the parasitic inductance of using flying-lead connectors and demonstrates how it destroys high-frequency signals. Even if the logic analyzer were able to sample fast enough, no signal makes it that far. But he doesn’t wave his hands around the problem — he shows you. And then he mentions hard-core-hacker-friendly tricks to get up into the hundreds of megahertz, with a hat-tip to [Bunnie Huang].

In our opinion sigrok, and the el cheapo hardware logic probes that it supports deserve a place in every hacker’s toolbox. This video is the best introduction to the software, and the topic in general, that we’ve ever seen.

We’ve featured two other videos from the [OpenTechLab], one on the ICE40 FPGA and one on high-frequency synthesis, that you might also like. So put away whatever brain-rotting Hollywood blockbuster you have on the shelf, and make some popcorn for quality nerd time.

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