How a quarter shrinker works

This machine is capable of shrinking coins. What you’re looking at is actually a 3D model of the Geek Groups impulse generator, which is called Project Stomper. The model is used to explain how induction shrinks a quarter to the size of a dime.

The grey chamber to the left is a reinforced containment device. It’s a safety feature to keep people in the same room as the Stomper safe from flying particles which may result from the forces this thing can put out. You see, it uses a mountain of magnetic energy to compress the edges of a coin in on itself.

As the video after the break illustrates, the main part of the machine on the right starts off by boosting mains voltage using a microwave oven transformer. This gets the AC to 2000V, which is then rectified and boosted further to get to 6000V DC. This charges three huge parallel capacitors which are then able to source 100,000A at 6 kV. When it comes time to fire, the charge is dumped into a coil which has the coin at its center. The result is the crushing magnetic field we mentioned earlier.

This isn’t a new concept, we featured a different coin crusher build in the early years of Hackaday’s existence.

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Simple concepts behind complex coilguns

Coil guns use electromagnetic coils to propel a metal projectile. On the surface they may look rather complicated. But when you break down the concepts it’s pretty easy to learn. If you’ve ever thought of dabbling in this field this lengthy coilgun primer will be a great help.

The basic concept of a coilgun comes in three parts: the coil, the voltage source, and the switch that combines the two. In the build above you can see two spools of wire on the clear barrel of the gun. These make up a pair of accelerators which connect to those huge black capacitors supplying the voltage. The switch they used can’t really be seen but from the article we know it’s a Thyristor; a Silicon Controlled Rectifier (2N6504).

In the video after the break you can see these three parts coming together for a test firing. This is the first step in a longer journey. To achieve higher projectile velocities you must add coils, as in the image above. But spacing and timing quickly complicate the simple concept. But if you can work out all the kinks you end up with some pretty great hardware.

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[Quinn] resurrects an amplifier that experienced death-by-capacitor

[Quinn Dunki] is adding wireless audio to all of the rooms in her home. She’s going with Airplay, snatching up used or refurbished Airport Express units because of their ability to work with both her existing WiFi and the Airplay protocol. The last piece in the puzzle is to get an Amp and she chose the small unit seen above. The problem is that it was dead on arrival and she couldn’t get the company to respond to her issue. So she cracked it open and fixed it right up.

The offenders are the three electrolytic capacitors at the top of the picture. She took some close-up images of each and you can’t miss the fact that they’re blown out. These are often among the higher price-per-unit parts and manufactures try to pinch the penny as much as possible. Add to it the heat in a small enclosure like this one and you’ve got a failure. [Quinn] dug through her junk bin but the size of the replacement had to be a perfect match so she ended up putting in a parts order. The new caps fit and work perfectly as you can hear in the clip after the break.

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Automatic capacitor charger lets you have fun with sparks

[GranTotem] is delighted by the sparks put out when a capacitor is rapidly discharged. But he’s not impressed at the relatively slow process of connecting them to a power supply for a recharge. So he built this auto-charging station for his capacitors that provides a shockingly good time almost continuously. Check out the video to see what we mean.

We always like to see the guts of the project, and that’s why we chose this image for the feature. But when everything is properly seated in the project box [GranTotem] has managed to achieve a really clean look. There are two barrel jack connectors on the end, one for 16V and the other for 20V inputs. The lid of the enclosure hosts an on/off switch, adjustment knob, and two banana connector terminals. Once switched on, a relay connects and disconnects the capacitor from the power supply at regular intervals which are adjusted by the knob. Just connect a couple of probes to those banana terminals and let the sparks reign down.

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Polish your understanding of capacitors by building this meter

Building a capacitance meter is a great exercise. If you’re feeling quite safe in your digital-circuit-only life, this will push just far enough out of the comfort zone for you to see there’s nothing to fear in adding analog circuits to your designs. Here, [Raj] compares a voltage divider and RC timer to calculate the value of a capacitor. The project is aimed at teaching the concepts, and will be easy to follow for anyone who has at least a bit of experience working with a programmable microcontroller.

The meter is based on an established equation that uses are starting and ending voltage, as well as the time it took to transition between the two, to calculate capacitance. The capacitor will be charged from 0 volts to 0.5 volts. Using the built-in analog comparator is the easiest way to do this. [Raj] breadboarded a voltage divider to establish a 0.5V reference on one of the comparator’s pins. The other input comes from a circuit that places a resistor in line with the capacitor being tested. When that reading rises above the 0.5 volt reference the comparator match will be tripped, stopping a timer that had been running during the charge cycle. From there it’s just a matter of using the timer value in the calculation.

A capacitive discharge welder/cutter for all your lightweight needs

microspot-welder

[Radu Motisan] wrote in to share a cool project he has been working on lately, a pulsed microspot welder/cutter.

The device is capable of spot welding thin metals such as foils and battery tabs by sending a pair of high current pulses between the two electrodes whenever [Radu] presses the trigger button. The cutting portion of his device uses the same general mechanism, though it requires a far greater number of pulses to get the work done.

The welding/cutting process is controlled by an ATMega16, which is also tasked with taking input from the user and displaying information on the LCD panel. The microcontroller creates quick (in the ten to several hundred microsecond range) pulses for both welding and cutting, with the latter obviously requiring a long series of pulses.

[Radu] started out using a relatively small capacitor array to power the device, but has recently upgraded to a 1.6 Farad car audio capacitor, which works (and looks) much better than before. His blog seems to update every few days with more pictures and details about his welding station, so be sure to check back often for updates.

Be sure to stick around to see a short video of [Radu] adding metal tabs to batteries and tearing down an aluminum can with his cutter.

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Doubling up on the USB supercap flashlight

[Antoine] wrote in to let us know that he soldiers on with his flashlight project. He’s doubled up on the supercaps and tripled the LEDs (translated).

The core concept has stayed the same since the original version. He wanted a flashlight that was small and used no batteries. This iteration came about as he looked at increasing the light output of the device. He’s switched to some warm-white LEDs which are easier on the eyes, but was unhappy with the charge life now that he’s using current at a faster rate. The solution, of course, is more potential from the capacitor. He’s now using two 10 Farad caps in parallel. We are a little skeptical about his capacitor theory and ended up using this lecture to defog the issue of parallel and series capacitance.

The upgraded hardware is right at home in that plastic egg like you’d find in a coin-op trinket vending machine. You’ll see there’s still a colored LED to warn when the charge is getting too low.

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