Arduino PLC Keeps The Beat

For most of our prototype, hobby, or one-off electronics projects it’s perfectly fine to use a development platform like an Arduino Uno or something to that effect. They’re both easy to program and easy to wire up to projects without breaking the bank. But if you step into an industrial setting where reliability is paramount even in places that are noisy, vibrating all the time, hot, or otherwise unpleasant for electronics, you’ll want to reach for a programmable logic controller (PLC) that are much more robust. There is actually a PLC from Arduino, and if you want to dip your toes into the PLC world then take a look at this drum kit based on the Arduino Opta.

With the PLC at the core of the build, it’s on to making the drumming mechanisms themselves. For that, project creator [JC Audio] is using a series of solenoids attached to camera mounts with a custom 3D printed part that allows for quick assembly and disassembly so he can get the positioning of each drum sound just right. The high hat is taken care of by the noise of an internal solenoid, with the other drums striking various real drums and other solid objects in his shops. The solenoids themselves are driven by a solid-state relay expansion module to ensure there’s enough power

While the build doesn’t sit inside a factory and run for years at a time, a musician’s stage is certainly a rough enough environment that we might reach for a PLC over a standard development board for its benefits. The code for this project is available as well at the project’s GitHub page for those looking for a more advanced timekeeper to play along with their music practice, and for more details on why you might choose a PLC for your project take a look at this Arduino vs PLC showdown from a few years ago.

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Candle Powered Lantern Isn’t As Silly As You Think

[Gilles Messier] at the Our Own Devices YouTube channel recently took a look at an interesting device — an electric lantern powered by a candle. At first glance, this sounds completely absurd. Why use a candle to power LEDs when you can use the light from the candle itself? This gadget has a trick up its sleeve, though. It lets candle light out and uses the heat from the candle flame to generate power for the LEDs.

The small Peltier “solid-state heat pump” module in the lantern acts as a thermoelectric generator, converting heat from the candle into electricity for the LEDs. The genius of the device is how it handles the candle “exhaust”.  A bimetallic disk in the chimney of the lantern closes when the air inside the device is hot. The Peltier device converts the heat differential to electricity, causing the air inside the lantern to cool. Meanwhile, the candle is beginning to starve for oxygen.  Once the air cools down a bit, the disk bends, allowing stale smoke out, and fresh air in, allowing the candle to burn brightly again. Then the cycle repeats.

[Gilles] does a deep dive into the efficiency of the lantern, which is worth the price of admission alone. These lanterns are pretty expensive — but Peltier modules are well-known by hackers. We’re sure it won’t be too hard to knock together a cheap version at home.

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New Solar Spheres Claim To Be Better Than Solar Panels

When you think of solar energy, you probably think of flat plates on rooftops. A company called WAVJA wants you to think of spheres. The little spheres, ranging from one to four inches across, can convert light into electricity, and the company claims they have 7.5 times the output of traditional solar panels and could later produce even more. Unfortunately, the video below doesn’t have a great deal of detail to back up the claims.

Some scenes in the video are clearly forward-looking. However, the so-called photon energy system appears to be powering a variety of real devices. It’s difficult to assess some of the claims. For example, the video claims 60 times the output of a similar-sized panel. But you’d hardly expect much from a tiny 4-inch solar panel.

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The Thermite Process Iron Foundry

The thermite process is a handy way to generate molten iron in the field. It’s the reaction between aluminium metal and iron oxide, which results in aluminium oxide and metallic iron. It’s hot enough that the iron is produced as a liquid, which means it’s most notably used for in-field welding of things such as railway tracks. All this is grist to [Cody’s Lab]’s mill of course, so in the video below the break he attempts to use a thermite reaction in a rough-and-ready foundry, to make a cast-iron frying pan.

Most of the video deals with the construction of the reaction vessel and the mold, for which he makes his own sodium silicate and cures it with carbon dioxide. The thermite mix itself comes from aluminium foil and black iron oxide sand, plus some crushed up drinks cans for good measure.

The result is pretty successful at making a respectable quantity of iron, and his pour goes well enough to make a recognizable frying pan. It has a few bubbles and a slight leak, but it’s good enough to cook an egg. We’re sure his next try will be better. Meanwhile this may produce a purer result, but it’s by no means the only way to produce molten iron on a small scale.

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How To Turn Cheap Speakers Into Something A Little Better

[Adam Francis] bought some cheap speaker drivers from AliExpress. Are they any good? Difficult to tell without a set of enclosures for them, so he made a set of transmission line cabinets. The resulting video proves that a decent sounding set of speakers shouldn’t have to cost the earth, and is quite entertaining to watch.

The design he’s going for is a transmission line, in effect a folded half-wave resonant tube terminated at one end and open at the other, with the speaker close to half way along. There is a lot of nuance to perfecting a speaker cabinet, but this basic recipe doesn’t have to be optimum to give a good result.

So after having some MDF cut to shape and glueing it all together, he ends up with some semi decent speakers for not a lot of money. The video is entertaining, with plenty of Britishisms, but the underlying project is sound. We’d have a pair on our bench.

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Useless Robot Gets Cute, Has Personality

Useless robots (or useless machines) are devices that, when switched on, exist only to turn themselves back off. They are fun and fairly simple builds that are easy to personify, and really invite customization by their creators. Even so, [tobychui]’s Kawaii Useless Robot goes above and beyond in that regard. Not only will his creation dutifully turn itself off, but if the user persists in engaging it, Kawaii Useless Robot grows progressively (and adorably) upset which ultimately culminates in scooting about and trying to run away.

If anything, it gets cuter when upset.

This is actually a ground-up re-imagining of an original work [tobychui] saw from a Japanese maker twelve years ago. That original Kawaii Useless Robot did not have any design details, so [tobychui] decided to re-create his own.

Behind the laser-cut front panel is a dot matrix LED display made up of eight smaller units, and inside are a total of four motors, an ESP32 development board, and supporting electronics. A neat touch is the ability to allow connections over Wi-Fi for debugging or remote control. The project page has some nice photos of the interior that are worth checking out. It’s a very compact and efficient build!

Watch it in action in the video (embedded below) which also includes a tour of the internals and a thorough description of the functions.

Inspired to make your own useless machine? Don’t be afraid to re-invent the whole concept. For example, we loved the one that physically spins the switch and the clock that falls to the floor when it detects someone looking at it. That last one is a close relative of the clock that displays the wrong time if and only if someone is looking.

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Cavity Filters, The Black Art You Have A Chance Of Pursuing

A tuned circuit formed by a capacitor and an inductor is a familiar enough circuit, and it’s understood that it will resonate at a particular frequency. As that frequency increases, so the size of the capacitor and inductor decrease, and there comes a point at which they can become the characteristic capacitance and inductance of a transmission line. These tuned circuits can be placed in an enclosure, at which they can be designed for an extremely high Q factor, a measure of quality, and thus a very narrow resonant point. They are frequently used as filters for that reason, and [Fesz] is here with a video explaining some of their operation and configurations.

Some of the mathematics behind RF design can be enough to faze any engineer, but he manages to steer a path away from that rabbit hole and explain cavity filters in a way that’s very accessible. We learn how to look at tuned circuits as transmission lines, and the properties of the various different coupling methods. Above all it reveals that making tuned cavities is within reach.

They’re a little rare these days, but there was a time when almost every TV set contained a set of these cavities which were ready-made for experimentation.

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