Author: Al Williams

4364 Articles

Heart Rate Monitoring Via WiFi

September 5, 2025 by 22 Comments

Before you decide to click away, thinking we’re talking about some heart rate monitor that connects to a display using WiFi, wait! Pulse-Fi is a system that monitors heart rate using the WiFi signal itself as a measuring device. No sensor, no wires, and it works on people up to ten feet away.

Researchers at UC Santa Cruz, including a visiting high school student researcher, put together a proof of concept. Apparently, your heart rate can modify WiFi channel state information. By measuring actual heart rate and the variations in the WiFi signal, the team was able to fit data to allow for accurate heart rate prediction.

The primary device used was an ESP32, although the more expensive Raspberry Pi performed the same trick using data generated in Brazil. The Pi appeared to work better, but it is also more expensive. However, that implies that different WiFi chipsets probably need unique training, which, we suppose, makes sense.

Like you, we’ve got a lot of questions about this one — including how repeatable this is in a real-world environment. But it does make you wonder what we could use WiFi permutations to detect. Or other ubiquitous RF signals like Bluetooth.

No need for a clunky wristband. If you could sense enough things like this, maybe you could come up with a wireless polygraph.

Tips For Homebrewing Inductors

September 4, 2025 by 5 Comments

How hard can it be to create your own inductors? Get a wire. Coil it up. Right? Well, the devil is definitely in the details, and [Nick] wants to share his ten tips for building “the perfect” inductor. We don’t know about perfect, but we do think he brings up some very good points. Check out his video below.

If you are winding wire around your finger (or, as it appears in the video, a fork) or you are using a beefy ferrite core, you’ll find something interesting in the video.

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Optimizing VLF Antennas

September 4, 2025 by 12 Comments

Using digital techniques has caused a resurgence of interest in VLF — very low frequency — radio. Thanks to software-defined radio, you no longer need huge coils. However, you still need a suitable antenna. [Electronics Unmessed] has been experimenting and asks the question: What really matters when it comes to VLF loops? The answer he found is in the video below.

This isn’t the first video about the topic he’s made, but it covers new ground about what changes make the most impact on received signals. You can see via graphs how everything changes performance. There are several parameters varied, including different types of ferrite, various numbers of loops in the antenna, and wire diameter. Don’t miss the comment section, either, where some viewers have suggested other parameters that might warrant experimentation.

Don’t miss the 9-foot square antenna loop in the video. We’d like to see it suspended in the air. Probably not a good way to ingratiate yourself with your neighbors, though.

Between software-defined radio and robust computer simulation, there’s never been a better time to experiment with antennas and radios. We first saw these antennas in an earlier post. VLF sure is easier than it used to be.

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CPU Utilization Not As Easy As It Sounds

September 4, 2025 by 12 Comments

If you ever develop an embedded system in a corporate environment, someone will probably tell you that you can only use 80% of the CPU or some other made-up number. The theory is that you will need some overhead for expansion. While that might have been a reasonable thing to do when CPUs and operating systems were very simple, those days are long gone. [Brendan Long] explains at least one problem with the idea in some recent tests he did related to server utilization.

[Brendan] recognizes that a modern CPU doesn’t actually scale like you would think. When lightly loaded, a modern CPU might run faster because it can keep other CPUs in the package slower and cooler. Increase the load, and more CPUs may get involved, but they will probably run slower. Beyond that, a newfangled processor often has fewer full CPUs than you expect. The test machine was a 24-core AMD processor. However, there are really 12 complete CPUs that can fast switch between two contexts. You have 24 threads that you can use, but only 12 at a time. So that skews the results, too.

Of course, our favorite problem is even more subtle. A modern OS will use whatever resources would otherwise go to waste. Even at 100% load, your program may work, but very slowly. So assume the boss wants you to do something every five seconds. You run the program. Suppose it is using 80% of the CPU and 90% of the memory. The program can execute its task every 4.6 seconds. So what? It may be that the OS is giving you that much because it would otherwise be idle. If you had 50% of the CPU and 70% of the memory, you might still be able to work in 4.7 seconds.

A better method is to have a low-priority task consume the resources you are not allowed to use, run the program, and verify that it still meets the required time. That solves a lot of [Brendan’s] observations, too. What you can’t do is scale the measurement linearly for all these reasons and probably others.

Not every project needs to worry about performance. But if you do, measuring and predicting it isn’t as straightforward as you might think. If you are interested in displaying your current stats, may we suggest analog? You have choices.

CP/M Gently

September 3, 2025 by 13 Comments

If you are interested in retrocomputers, you might be like us and old enough to remember the old systems and still have some of the books. But what if you aren’t? No one is born knowing how to copy a file with PIP, for example, so [Kraileth] has the answer: A Gentle Introduction to CP/M.

Of course, by modern standards, CP/M isn’t very hard. You had disks and they had a single level of files in them. No subdirectories. We did eventually get user areas, and the post covers that near the end. It was a common mod to treat user 0 as a global user, but by default, no.

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The (RF) Sniff Test

August 29, 2025 by 12 Comments

Sometimes the old tricks are the best. [Kevin] learned an old trick about using a ‘scope to sniff RF noise and pays it forward by sharing it in a recent video. He uses an oscilloscope. But does he need some special probe setup? Nope. He quickly makes a little RF pickup probe, and if you have a ‘scope, we’re pretty sure you can make one in a few seconds, too.

Of course, you can get probes made for that, and there are advantages to using them. But the quick trick of quickly and non-destructively modifying the existing probe to pick up RF means you always have a way to make these measurements.

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Hackaday Podcast Episode 335: Beer, Toast, And Pi

August 29, 2025 by 3 Comments

What happens when you listen in on Elliot Williams and Al Williams? You get a round up of the best of last week’s Hackaday posts, of course. The topics this week range from beer brewing to lightning protection, with a little bit of everything in between.

This week, many problems find solutions. Power drill battery dead? Your car doesn’t have a tire pressure monitor? Does your butter tear up your toast? You can find the answer to these problems, and more, on the Hackaday podcast.

For the can’t miss section, the guys are annoyed that Google wants to lock down their phones, and also talk about measuring liquid levels in outer space.

Check out the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Or download in DRM-free MP3 without requiring developer registration.

Where to Follow Hackaday Podcast

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