Author: Al Williams

4335 Articles

Trace Tracing To The Tunes

January 1, 2026 by 2 Comments

Some kind of continuity beeper has been a standard piece of gear since the dawn of electronics. Sure, you probably have an ohm meter, but sometimes you don’t care about the actual resistance. You just want to know whether something connects or doesn’t, especially with a PCB trace or a cable. But what if your beeper could tell you more? [Nick Cornford] asks and answers that question with a beeper that lets you estimate resistance via pitch.

The circuit is relatively simple. A short to ground causes a voltage divider to produce a fraction of the battery voltage and a FET to conduct that fractional voltage to a VCO via a high-gain amplifier. The VCO converts voltage to frequency, and an audio amplifier feeds it to the speakers.

The two amplifiers and the VCO require two dual op-amp chips. The original schematic sends the output to some relatively high-impedance headphones. To drive more practical ones, the circuit can drop one op amp and use another FET and a separate battery.

Of course, you have many design choices, especially for the audio amplification. There are plenty of VCO circuits, or you could probably substitute a small microcontroller with an A/D converter and PWM output. Yes, you can also make a VCO with a 555.

VCOs are common because they are at the heart of PLLs.

Linux Fu: Compose Yourself!

December 30, 2025 by 15 Comments

Our computers can display an astonishing range of symbols. Unicode alone defines more than 150,000 characters, covering everything from mathematical operators and phonetic alphabets to emoji and obscure historical scripts. Our keyboards, on the other hand, remain stubbornly limited to a few dozen keys.

On Windows, the traditional workaround involves memorizing numeric codes or digging through character maps. Linux, being Linux, offers something far more flexible: XCompose. It’s one of those powerful, quietly brilliant features that’s been around forever, works almost everywhere, and somehow still feels like a secret.

XCompose is part of the X11 input system. It lets you define compose sequences: short key sequences that produce a Unicode character. Think of it as a programmable “dead key” system on steroids. This can be as simple as programming an ‘E’ to produce a Euro sign or as complex as converting “flower” into a little flower emoji. Even though the system originated with X11, I’ve been told that it mostly works with Wayland, too. So let’s look deeper.

Continue reading “Linux Fu: Compose Yourself!” →

Redneck Spaceship From Trash

December 25, 2025 by 7 Comments

Facebook Marketplace provides you with a free grain silo, so what do you do with it? If you are [saveitforparts], you mix it with other materials and produce a retro-style rocket ship prop. Art project? Sure, we’ll call it that.

We have to admit, we also see rockets in everyday objects, and the silo does look the part. He also had some junk that looked like a nose cone, some tanks, and other assorted trash.

Continue reading “Redneck Spaceship From Trash” →

Roll Your Own Hall Effect Sensor

December 24, 2025 by 8 Comments

If you read about Hall effect sensors — the usual way to detect and measure magnetic fields these days — it sounds deceptively simple. There’s a metal plate with current flowing across it in one direction, and sensors at right angles to the current flow. Can it really be that simple? According to a recent article in Elektor, [Burkhard Kainka] says yes.

The circuit uses a dual op amp with very high gain, which is necessary because the Hall voltage with 1 A through a 35 micron copper layer (the thickness on 1 oz copper boards) is on the order of 1.5 microvolts per Tesla. Of course, when dealing with tiny voltages like that, noise can be a problem, and you’ll need to zero the amplifier circuit before each use.

The metal surface? A piece of blank PCB. Copper isn’t the best material for a Hall sensor, but it is readily available, and it does work. Of course, moving the magnet can cause changes, and the whole thing is temperature sensitive. You wouldn’t want to use this setup for a precision measurement. But for an experimental look at the Hall effect, it is a great project.

Today, these sensors usually come in a package. If you want to know more about the Hall effect, including who Edwin Hall was, we can help with that, too.

Using An E-Book Reader As A Secondary Display

December 23, 2025 by 14 Comments

[Alireza Alavi] wanted to use an e-ink tablet as a Linux monitor. Why? We don’t need to ask. You can see the result of connecting an Onyx BOOX Air 2 to an Arch Linux box in the video below.

Like all good projects, this one had a false start. Deskreen sounds good, as it is an easy way to stream your desktop to a browser. The problem is, it isn’t very crisp, and it can be laggy, according to the post. Of course, VNC is a tried-and-true solution. The Onyx uses Android, so there were plenty of VNC clients, and Linux, of course, has many VNC servers.

Putting everything together as a script lets [Alireza] use the ebook as a second monitor. Using it as a main monitor would be difficult, and [Alireza] reports using the two monitors to mirror each other, so you can glance over at the regular screen for a color image, for example.

Another benefit of the mirrored screens is that VNC lets you use the tablet’s screen as an input device, which is handy if you are drawing in GIMP or performing similar tasks.

We sometimes use VNC on Android just to get to a fake Linux install running on the device.

Continue reading “Using An E-Book Reader As A Secondary Display” →

Improving The Cloud Chamber

December 19, 2025 by 8 Comments

Want to visualize radioactive particles? You don’t need a boatload of lab equipment. Just a cloud chamber. And [Curious Scientist] is showing off an improved miniature cloud chamber that is easy to replicate using a 3D printer and common components.

The build uses a Peltier module, a CPU cooler, an aluminum plate, thermal paste, and headlight film. The high voltage comes from a sacrificed mosquito swatter. The power input for the whole system is any 12V supply.

The cloud chamber was high tech back in 1911 when physicist Charles T. R. Wilson made ionizing radiation visible by creating trails of tiny liquid droplets in a supersaturated vapor of alcohol or water. Charged particles pass through, leaving visible condensation trails.

Continue reading “Improving The Cloud Chamber” →

The Miracle Of Color TV

December 18, 2025 by 36 Comments

We’ve often said that some technological advancements seemed like alien technology for their time. Sometimes we look back and think something would be easy until we realize they didn’t have the tools we have today. One of the biggest examples of this is how, in the 1950s, engineers created a color image that still plays on a black-and-white set, with the color sets also able to receive the old signals. [Electromagnetic Videos] tells the tale. The video below simulates various video artifacts, so you not only learn about the details of NTSC video, but also see some of the discussed effects in real time.

Creating a black-and-white signal was already a big deal, with the video and sync presented in an analog AM signal with the sound superimposed with FM. People had demonstrated color earlier, but it wasn’t practical for several reasons. Sending, for example, separate red, blue, and green signals would require wider channels and more complex receivers, and would be incompatible with older sets.

Continue reading “The Miracle Of Color TV” →