You Should Not Try These Taser NERF Darts

For most of us, a good part of our childhood involved running around someone’s backyard (or inside the house) trying to score hits with a toy NERF gun. The fun level was high and the risk of personal injury was low. Now that we’re all mostly adults, it’s probably time to take our NERF game to the next level with some risk of serious personal harm.

In an effort to help his brother get back at him for being somewhat of a bully in their youth, [Allen Pan] gifted him with an upgraded NERF gun. Specifically, one with darts that pack a punch. Each of the “Elite” darts was equipped with a 300 V capacitor packed into the interior of the dart. New tips were 3D printed with special metal tips that allow the capacitor to discharge upon impact.

Besides the danger, there’s a good bit of science involved. Parts were scavenged from a new (and surprisingly expensive) disposable camera, and a customized circuit was constructed around the barrel of the dart gun that allows the darts to charge up when they’re loaded. It’s an impressive build that would be relatively simple to reconstruct for yourself, but it’s probably not the worst thing we’ve seen done with high voltage and a few small capacitors.

Thanks to [Itay] for the tip!

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Low-Quality Capacitors Turned Into High-Quality Temperature Sensors

When life hands you a bunch of crummy capacitors, what do you do? Make a whole bunch of temperature sensors, apparently.

The less-than-stellar caps in question came to [pyromaniac303] by way of one of those all-in-one assortment kits we so love to buy. Stocked with capacitors of many values, kits like these are great to have around, especially when they’ve got high-quality components in them. But not all ceramic caps are created equal, and [pyromaniac303] was determined not to let the lesser-quality units go to waste. A quick look at the data sheets revealed that the caps with the Y5V dielectric had a suitably egregious temperature coefficient to serve as a useful sensor. A fleck of perf-board holds a cap and a series resistor; the capacitor is charged by an Arduino output pin through the resistor, and the time it takes for the input pin connected to the other side of the cap to go high is measured. Charge time is proportional to temperature, and a few calibration runs showed that the response is pretty linear. Unfortunately the temperature coefficient peaks at 10°C and drops sharply below that point, making the sensor useful only on one side of the peak. Still, it’s an interesting way to put otherwise unloved parts to use, and a handy tip to keep in mind.

Temperature sensing isn’t the only trick capacitors can do. We’ve seen them turned into touch sensors before, and used to turn a 3D-printer into a 3D-scanner.

Replace Old Electrolytics? Not So Fast… Maybe

[CuriousMarc] was restoring an old Model 19 TeleType. The design for these dates back to the 1930s, and they are built like tanks (well, except for the ones built during the war with parts using cheaper metals like zinc). Along the way, he restored a hefty tube-based power supply that had two very large electrolytic capacitors. These dated from the 1950s, and common wisdom says you should always replace old electrolytics because they don’t age well and could damage the assembly if powered up. [Marc] didn’t agree with common wisdom, and he made a video to defend his assertion which you can see below.

If you look at the construction of electrolytic capacitors, one plate of the capacitor is actually a thin layer that is formed electrically. In some cases, a capacitor with this plate is damaged can be reformed either by deliberate application of a constant current or possibly even just in normal operation.

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You Can Now Buy a Practical Gauss Gun

Occasionally we come across a piece of information which reminds us that, while flying cars are still nowhere to be found, we’re definitely living in the future. Usually it’s about some new application of artificial intelligence, or maybe another success in the rapidly developing field of private spaceflight. But sometimes it’s when you look at a website and say to yourself: “Oh cool, they have 1.5kW electromagnetic accelerators in stock.”

Arcflash Labs, a partnership between [David Wirth] and [Jason Murray], have put their EMG-01A Gauss gun up for sale for anyone who’s brave enough and willing to put down $1,000 USD on what’s essentially a high-tech BB gun. The creators claim it obtains an efficiency of 6.5% out of its RC-style 6S LiPo battery pack, which allows it to fire over 100 rounds before needing to be recharged. Firing 4.6g steel projectiles at a rather leisurely 45 m/s, this futuristic weapon would be more of a match for tin cans than invading alien forces, but at least you’ll be blasting those cans from a position of supreme technical superiority.

The EMG-01A builds on the work of the team’s previous experiments, such as the semi-automatic railgun we covered last year. They’ve made the device much smaller and lighter than their previous guns, as well as worked on making them safer and more reliable. That said, the page for the EMG-01A has a number of warnings and caveats that you won’t see on the back of a Red Ryder BB gun box; it’s certainly not a toy, and anyone who takes ownership of one needs to be respectful of the responsibility they’re taking on.

Speaking of which, who can actually buy one of these things? The Arcflash Labs site makes it clear they will only ship to the United States, and further gives a list of states and cities were they can’t send a completed gun. Essentially they are following the same laws and guidelines used for shipping air guns within the US, as they believe that’s a fair classification for their electromagnetic guns. Whether or not the ATF feels the same way is unclear, and it should be interesting to see what kind of legal response there may be if Arcflash Labs starts moving enough units.

If you’d like to wage warfare on your recyclables without spending quite so much cash, you can always build your own for less. Or nearly nothing, if you want to go the full MacGyver route.

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These Capacitors are a Cheap Gimmick

If you search through an electrical engineering textbook, you probably aren’t going to find the phrase “gimmick capacitor” but every old ham radio operator knows about them. They come in handy when you need a very small capacitor of unknown value. For example, if you are trying to balance the stray capacitance in a circuit, you might not know exactly what value you need, but you know it won’t be very much. That’s when you want a gimmick capacitor.

A gimmick capacitor is made by taking two strands of insulated wire and twisting them together; the length and the tightness of the twist determine the capacitance. Tightening or loosening the twist, or trimming some of the wire off, makes it tunable.

These are most commonly found in RF equipment or high-speed logic because of the small capacitance involved — usually about 1 to 2 pF per inch of twist or so. The thicker the insulation, the less capacitance you’ll get, so it is common to use magnet wire or something else with a thin insulating layer. You can take this one step further and decrease the spacing by stripping down one wire as long as it isn’t going to touch anything else.

Obviously, the insulation needs to be good enough for the voltage on them, an important consideration in tube circuits, for instance. But other than that, a gimmick capacitor is a straightforward tool to have in your box of design tricks. Can we take this further? Continue reading “These Capacitors are a Cheap Gimmick”

A Bit More Than A Microphone: The Electret Story

When designing a microphone assembly the other day, I reached for an electret condenser microphone capsule without thinking. To be strictly accurate I ordered a pack of them, these small cylindrical microphones are of extremely high quality for their relatively tiny price.

It was only upon submitting the order that I had a thought for the first time in my life: Just what IS an electret condenser microphone?

A condenser microphone is easy enough to explain. It’s a capacitor formed from a very thin conductive sheet that functions as the diaphragm, mounted in front of another conductor, usually a piece of mesh. Sound waves cause the diaphragm to vibrate, and these vibrations change the capacitance between diaphragm and mesh.

If that capacitance is incorporated into an RC circuit with a very high impedance and a high voltage is applied, a near constant charge is placed upon it. Since the charge stays constant, changing the capacitance causes a tiny voltage fluctuation that can be retrieved as the audio signal from the microphone. Condenser microphones built in this way can be extremely high quality, but come at the expense of needing a high voltage power supply to supply the charge and an amplifier to buffer and magnify the audio.

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Creality CR10-S Upgrade Shows The Effect Of Bad Power

The Creality CR10-S is a printer that has become quite popular, and is not an uncommon sight in a hackspace or makerspace. Some models have a slight defect, a smoothing capacitor is of insufficient size, resulting in reduced print quality. [Jozerworx] has replaced the capacitor, and posted a full guide as to how the task can be performed.

Hackaday readers will have among their number many for whom replacing a surface mount electrolytic is no bother at all, indeed we’d expect most 3D printer owners to be able to perform the task. Maybe that the post has such an extensive FAQ and seems to be aimed at newbies to soldering points to 3D printing having moved to a wider market. But it has to be remembered that the value in this piece is not in the work, but in the characterisation. At the end he posts graphs showing the effect of the modification on the temperature of the extruder, and on the temperature noise brought about by the poor capacitor choice. A reduction from a +/- 3 Celcius variation to one of around +- 0.1 Celcius may not seem like much, but it seems it has a significant effect on the reliability of the printer.

So this isn’t the most elite of hacks, on a printer heading for a wider marketplace. But it serves to illustrate that bad quality power regulation can have some surprising effects. It seems every new printer comes with a list of community-developed mods to make it usable, perhaps one day we’ll find a printer that’s at peak performance out-of-the-box.