Swap Your Microwave For A High Voltage Stereo

When building a new project, common wisdom suggests to avoid “reinventing the wheel”, or doing something simple from scratch that’s easily available already. However, if you can build a high-voltage wheel, so to speak, it might be fun just to see what happens. [Dan] decided to reinvent not the wheel, but the speaker, and instead of any conventional build he decided to make one with parts from a microwave and over 6,000 volts.

The circuit he constructed works essentially like a Tesla coil with a modulated audio signal as an input. The build uses the high voltage transformer from the microwave too, which steps the 240 V input up to around 6 kV. To modulate that kind of voltage, [Dan] sends the audio signal through a GU81M vacuum tube with the support of a fleet of high voltage capacitors. The antenna connected to the magnetron does tend to catch on fire somewhere in the middle of each song, so it’s not the safest device around even if the high voltage can be handled properly, but it does work better than expected as a speaker.

If you want a high-voltage speaker that (probably) won’t burn your house down, though, it might be best to stick to a typical Tesla coil. No promises though, since working with high voltages typically doesn’t come with safety guarantees.

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Enforce Social Distancing With High Voltage

When getting parts together for a one-off project, we often find ourselves with some leftovers on hand. Most of the time these things go in the junk drawer, but [Brad] aka [AtomicZombie] was working on a project which required parts salvaged from several microwave ovens. That left him with enough surplus components to build a social distancing enforcement tool for the modern age; which will deliver a taser-like shock to anyone which violates the new six-foot rule.

The leftover parts in question were built around a high-voltage capacitor, which [Brad] strapped to his back to hold all of the electronics needed for the six-foot electrified hoop. The generator utilizes the output voltage from two magnetrons, but doesn’t start until the operator enters a code on the front control panel, which is about the only safety device on this entire contraption. To get power to the magnetrons a 12 VDC car battery is used with an inverter to get the required input voltage, and towards the end of the video linked below he shows its effectiveness by setting various objects on fire with it.

While this gag project is unlikely to get any actual use, it’s not like any of us around here need an excuse to play with high voltages. [Brad] is also unlikely to need it either; he lives on a secluded 100-acre homestead and has been featured here for some of the projects he built to make his peaceful life a little easier, like a robotic laundry line, mobile chicken coop, and an electric utility tricycle built from an old truck and motorcycle.

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Link Coupling Antenna Tuner Wordless Workshop

Remember “Wordless Workshop” in Popular Science? [Roy Doty] illustrated a household problem and the solution for it cobbled up in the main character’s garage workshop. We wonder what [Roy] would have done with YouTube? Maybe something like the video from [VE2TAE] and [VE2AEV] showing their link coupling antenna tuning build. You can watch the video after the break, and if you aren’t a fan of Jazz, you can mute the volume.

Like [Doty’s] cartoons, the video presumes you are going to have your own idea about dimensions and component values to fit your needs. But the construction is beautiful in its own right. The tubing wound into giant coils is impressive and brings back memories of the old days. However, the construction of the variable capacitors really got us excited. Big air variable caps may be hard to find, but the video makes them look easy to make.

A couple of nice looking knobs and panel meters make for a great looking tuner. With that spacing, we imagine it would handle full legal power without any difficulty at all. If you want to learn more about this type of tuner, [VK1OD] had a great page about it which seems to be defunct now. But the Internet Archive comes to our rescue, as usual.

The design is quite old, so even a 1934 copy of “Radio” can explain it (look on page 6). If you want to see a more wordy example of making variable capacitors — although they are smaller, the same principles apply — [N4DFP] has a good write up for that.

Of course, these days, most people expect their antenna tuning to be automatic. With some Lego, though, you could refit your manual one, if you like.

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Hybrid Supercapacitors Are — Well — Super

Kurt.energy is promoting a new line of hybrid supercapacitors. By itself, that wouldn’t be very newsworthy, but the company claims these graphene-based supercapacitors merge the best features of both supercapacitors and lithium-ion batteries. Based on technology from a company called Shenzhen Toomen New Energy, the capacitors are optimized for either high energy or high power. They can reportedly charge and discharge 10-20 times faster than lithium-ion batteries. Of course, we’ve heard wild claims surrounding graphene capacitors before and, so far, they haven’t seemed very credible.

In addition to high performance, the company claims the capacitors are safe from overcharging, short circuit, and other safety issues that plague batteries. The devices are said to operate — including charging — from -40C to 80C. You can see a video from the company, below.

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Fixing The Flicker Afflicting A Night Light

It’s hard to part with some things, even if they’re broken and were worth next to nothing to begin with. But some things are just special, y’know? And we would say in this case, the thing was definitely worth saving.

[Taste the Code]’s daughter’s beloved night light had a terrible flickering problem, and then stopped working altogether. Eager to make her happy, he cracked it open and found that one of the wires had disconnected from the outlet pin it was soldered to. That’s a simple enough fix, but trying to solder in tight quarters where the walls are soft plastic can be quite challenging.

Once that was fixed, [Taste the Code] plugged it in to a test outlet. It’s back to working, but also back to flickering, because there is no capacitor to smooth out the signal going to the LEDs. [Taste the Code] measured the voltage drop across the output of the bridge rectifier and soldered in an electrolytic cap with more than double the necessary voltage rating, just to be safe. You can check out the video after the break.

This goes to show several things: one, you can learn from fixing and improving cheap electronics from the likes of your local dollar store. Two, you can also get some kinds of components there quite inexpensively from things like magnetic sensor-based window alarms and dirt cheap solar garden lights.

You can also do some fun stuff with those cheap IKEA lamps designed for children. Here’s an adorable cloud lamp with an RGB LED upgrade that shows the weather mood using an ESP8266.

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LC Oscillators, Animated

We wish that all the beautiful animations that are available today to understand math and electronics had been around when we were in school. Nonetheless, they are there for today’s students and [Learn Engineering] has another gorgeous one covering LC oscillation. Check it out, below.

If you are thoroughly grounded — no pun intended — in LC circuits, you probably won’t learn anything new. However, the animations are worth watching, just to admire them, if nothing else.

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Horse Racing Game Hits Trifecta Of Fun, Skill, And Competition

Out in the neon-painted desert of Las Vegas, if you know where to look, you can find an old, 1980s electromechanical horse racing game called Sigma Derby. In this group game, you and several drunk strangers sit around a machine the size of a pool table and bet on tiny horses at 25 cents a throw. There is no skill involved, it’s all chance. This is not that game.

[Alex Kov]’s electromechanical horse racing game is a unicorn compared to Sigma Derby, or at least a zebra. This game takes patience, skill, and cunning. And unlike Sigma Derby, you can easily replicate it at home with a few shakes of the old junk bin. You just need a couple of motors, transistors, electrolytic caps, and some passives.

The idea is simple — advance horse, be first, win prizes — but it’s not that easy. While the switch is unpressed, the circuit charges up a capacitor. Press it and the horse noses forward, draining the cap. There is never enough chooch in the cap to reach the finish line, so the real game is in building up more juice than the other guy, and then staying ahead or overtaking him with the next spurt. Place your bets and catch the action after the break.

A scoreboard would be a great addition to this game. If you want to keep it electromechanical, we have some tote board inspiration for you.

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