Simplest Speaker Oscillator, Now Even Simpler

April 30, 2024 by Dan Maloney 17 Comments

It never fails. Lay down some kind of superlative — fastest, cheapest, smallest — around this place and someone out there says, “Hold my beer” and gets to work. In this case, it’s another, even simpler audio oscillator, this time with just a loudspeaker and a battery.

Attentive readers will recall the previous title holder was indeed pretty simple, consisting only of the mic and speaker from an old landline telephone handset wired in series with a battery. Seeing this reminded [Hydrogen Time] of a lucky childhood accident while experimenting with a loudspeaker, which he recreates in the video below. The BOM for this one is even smaller than the previous one — just a small speaker and a battery, plus a small scrap of solid hookup wire. The wire is the key; rather than connecting directly to the speaker terminal, it connects to the speaker frame on one end while the other is carefully adjusted to just barely touch the flexible wire penetrating the speaker cone on its way to the voice coil.

When power is applied with the correct polarity, current flows through the wire into the voice coil, which moves the cone and breaks the circuit. The speaker’s diaphragm resets the cone, completing the circuit and repeating the whole process. The loudspeaker makes a little click with each cycle, leading to a very rough-sounding oscillator. [Hydrogen Time] doesn’t put a scope on it, but we suspect the waveform would be a ragged square wave whose frequency depends on the voltage, the spring constant of the diaphragm, and the spacing between the fixed wire and the voice coil lead.

Yes, we realize this is stretching the definition of an audio oscillator somewhat, but you’ve got to admit it’s simple. Can you get it even simpler?

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VAR Is Ruining Football, And Tech Is Ruining Sport

April 29, 2024 by Lewin Day 68 Comments

Another week in football, another VAR controversy to fill the column inches and rile up the fans. If you missed it, Coventry scored a last-minute winner in extra time in a crucial match—an FA Cup semi-final. Only, oh wait—computer says no. VAR ruled Haji Wright was offside, and the goal was disallowed. Coventry fans screamed that the system got it wrong, but no matter. Man United went on to win and dreams were forever dashed.

Systems like the Video Assistant Referee were brought in to make sport fairer, with the aim that they would improve the product and leave fans and competitors better off. And yet, years later, with all this technology, we find ourselves up in arms more than ever.

It’s my sincere belief that technology is killing sport, and the old ways were better. Here’s why. Continue reading “VAR Is Ruining Football, And Tech Is Ruining Sport” →

No Active Components In This Mysterious Audio Oscillator

April 23, 2024 by Dan Maloney 39 Comments

What’s the simplest audio frequency oscillator you can imagine? There’s the 555, of course, and we can think of a few designs using just two transistors or even a few with just one. But how about an oscillator with no active components? Now there’s a neat trick.

Replicating [Stelian]’s “simplest audio oscillator on the Internet” might take some doing on your part, since it relies on finding an old telephone. Like, really old — you’ll need one with the carbon granule cartridge in the handset, along with the speaker. Other than that, all you’ll need is a couple of 1.5-volt batteries, wiring everything in one big series loop, and placing the microphone and speaker right on top of each other. Apply power and you’re off to the races. [Stelian]’s specific setup yielded a 2.4-kHz tone that could be altered a bit by repositioning the speaker relative to the mic. On the oscilloscope, the waveform is a pretty heavily distorted sine wave.

It’s a bit of a mystery to [Stelian] as to how this works without something to provide at least a little gain. Perhaps the enclosure of the speaker or the mic has a paraboloid shape that amplifies the sound just enough to kick things off? Bah, who knows? Let the hand-waving begin!

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Radio Frequency Burns, Flying A Kite, And You

April 21, 2024 by Lewin Day 22 Comments

Most hams can tell you that it’s possible to get a nasty RF burn if you accidentally touch an antenna while it’s transmitting. However, you can also cop a nasty surprise on the receiving end if you’re not careful, as explained in a video from [Grants Pass TV Repair].

*It’s hard to see in a still image, but the RF burns from the kite antenna actually generate a little puff of smoke on contact.*

An experiment was used to demonstrate this fact involving a kite and a local AM broadcaster. A simple calculation revealed that an antenna 368 feet and 6 inches long would be resonant with the KAJO Radio signal at 1.270 MHz. At half the signal’s wavelength, an antenna that long would capture plenty of energy from the nearby broadcast antenna.

Enter the kite, which served as a skyhook to loft an antenna that long. With the wire in the air picking up a strong signal from the AM radio tower, it was possible to get a noticable RF burn simply by touching the end of the antenna.

The video explains that this is a risky experiment, but not only because of the risk of RF burn itself. It’s also easy to accidentally get a kite tangled in power lines, or to see it struck by lightning, both of which would create far greater injuries than the mild RF burn seen in the video. In any case, even if you know what you’re doing, you have to be careful when you’re going out of your way to do something dangerous in the first place.

AM radio towers aren’t to be messed with; they’ve got big power flowing. Video after the break.

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Building A Giant Boardgame Isn’t Easy

April 19, 2024 by Lewin Day 8 Comments

[Stevenson Streeper] is a maker, and was recently charged with a serious mission. He had to prototype, design, and build a board game. A software-controlled board game, that is, and one that was 400 square-feet in size. As you might imagine, this ended up being a tall order, and he’s been kind enough to share his tale on his blog.

His client’s idea was for a giant interactive game board akin to the glowing disco floors of old. It had to play a game approximating the rules of “The Floor Is Lava.” It had to handle up to 20 players at a time, too.

[Stevenson] runs a company that delivers “Activations”—basically big showpieces for customers willing to pay. This wasn’t his first attempt at building an immersive attraction, but it was a big job, and a challenging one at that. He explains the difficulties that came about from a limited crew, limited timeline, and a number of difficult missteps. Hurdles included surprise unusable off-the-shelf hardware and the difficulty of hand-sanding 144 tiles of polycarbonate. One weeps for the project’s plight early on – if only the AliExpress tiles were documented.

He may have bitten off more than he could chew, and yet—the project was finished and to a decent degree of functionality success. That’s to be applauded, and [Stevenson] learned a ton along the way. Big projects can be daunting and can put you in a bind. As this story demonstrates, though, perseverance often gets you somewhere okay in the end. Video after the break.

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Roboticizing An Etch-a-Sketch

April 19, 2024 by Lewin Day 7 Comments

The Etch-a-Sketch was a popular toy, but a polarizing one. You were either one of those kids that had the knack, or one of the kids that didn’t. [Micah] was pretty firmly in the latter group, so decided to roboticize the Etch-a-Sketch so a computer could draw for him instead.

The build uses a pair of stepper motors attached to the Etch-a-Sketch’s knobs via 3D-printed adapters. It took [Micah] a few revisions to get the right design and the right motors for the job, but it all came together. A Raspberry Pi is charged with driving the motors to draw the desired picture.

Beyond the mechanics, [Micah] also does a great job of explaining the challenges around drawing and the drive software. Namely, the Etch-a-Sketch has a major limitation in that there’s no way to move the stylus without drawing a line. He accounts for this in his code for converting and drawing images.

The robot draws slowly but surely. The final result is incredibly impressive, and far exceeds what most of us could achieve on by hand. We’ve seen some similar builds in the past, too. Video after the break.

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Computing Via (Virtual) Dominos

April 18, 2024 by Al Williams 6 Comments

Back in 2012, [Matt Parker] and a team built a computer out of dominos for the Manchester Science Festival. [Andrew Taylor], part of the team that built the original, has built a series of virtual domino puzzles to help explain how the computer worked. He also links to a video from the event, but be warned: the video contains some spoilers for the puzzles. If you are ready for spoilers, you can watch the video below.

The original computer could add two three-bit numbers and provide a four-bit result. We don’t want to give away the answers, but the inverter is quite strange. If you don’t want to puzzle it out, you can press the “reveal answer” to see [Andrew’s] solutions. Press “play” and watch the dominos fall.

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