May 20, 2024

Saleae logic analyzer

These are very handy units for debugging all sorts of boards. they give you a “picture” of each signal coming from each wire probe that’s attached to your Device Under Test (DUT), and then you can correlate and try to understand which signals are doing what. They’re about $400, so it’s a little much for a hobbyist, but they do a ton of stuff. I have no idea how to pronounce the name and no resolve to figure it out, I just know they’re very handy 🙂

I have the Logic 8, which gives you the ability to look at 8 channels of data at the same time. For each channel there’s a ground so you can keep your signals cleaner. I didn’t use them all, but they’re there.

It has a nice GUI-based way to view data, which you can view on Windows, Mac or Linux, which is nice. You can download it here, it’s reasonably easy to set up. There’s a manual here too that’s actually pretty useful.

When you hook up the unit, it should look something like this:

Then you start up the software and set the amount of time you want to capture data for, I picked 30 seconds.

When it runs, it will try to guess what protocol it’s seeing with varying levels of success. You kind of have to know what you are looking for though, and set the trigger to capture what you’re interested in.

It will see standard voltage level logic levels, so no need to explicitly set them. I wouldn’t hook up the leads to a 110VAC outlet, but I think they’re good up to 5VDC (or more), which covers what you’ll likely use it on.

It can also show analog signals, in case that’s what you’re debugging, but usually that’s done with an oscilloscope.

In my case, I wanted to look at 5 channels for 30 seconds, which gave me a whopping 250MB of a file, but hey, you probably won’t need to sample something that long with that many channels. Here’s what I got:

I zoomed way in to be able to see this, which you can do with your arrow keys or mouse scrolling. You want to start by being zoomed way out and then look for little clumps of data, then zoom in and see what those clumps tell you about your signals.