Disposable Camera Coil Gun!

Some of the most enjoyable projects tend to have the terrible drawback of also having the most potential to cause bodily harm, like getting zapped by the capacitor when digging into a disposable camera. But often — if you’re careful — this curiosity pays off and you wind up learning how to make something cool like this coil gun from a camera flash’s capacitor. This handheld launches a small nail, and is packed in a handheld form factor with a light switch trigger.

[LabRatMatt] dispels any illusions of potential harm upfront and then repeatedly urges caution throughout his detailed guide. He breaks down the physics at work while maintaining a lighthearted tone. This coil gun uses a capacitor and charging circuit ripped from a disposable camera — [LabRatMatt] decided to double up with another capacitor that he had on hand from a previous project. The coil was repurposed from an old doorbell, but make sure to use a few hundred windings if you make your own coil. A light switch ended up being suitable for a trigger since it is able to handle the voltage spikes.

When assembled, it almost looks like something you’d expect to see in a post-apocalyptic wasteland, but it works!

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Touchless MIDI: The Secret’s In the Mitten

MIDI is a great tool for virtually any musician. Unless you’re a keyboard player, though, it might be hard to use it live. [Evan] recently came up with a great solution for all of the wistful guitar players out there who have been dreaming of having a MIDI interface as useful as their pianist brethren, though. He created a touchless MIDI controller that interfaces directly with a guitar.

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Forget Wifi or Bluetooth, Pair Directly With Your Phone’s Speaker

[Kedar Nimbalkar] hyperbolically advertises the ultimate cell phone speaker dock. It costs a dollar. It doesn’t need you to pair with it via Bluetooth or WiFi. It pairs extremely fast, 0.000000000001, he clarifies. It may also look like a broken laptop speaker with a stomped wall wart soldered to it, but who can keep up with industrial design trends these days?

He shows us the device in operation. He starts playing some music on his phone’s speaker. It’s not very loud, so he simply lays the phone on the dock. Suddenly, all the audio fidelity a Dell Lattitude from the 90s can provide erupts from the device! How is this done?

Of course, there’s not much to the trick. Since the cellphone speaker is a coil it can induce a small current in another coil. The resulting voltage can be picked up by an audio amplifier and played through the speakers. Nonetheless it’s pretty cool, and we like his suggestion of betting our friends that we could wirelessly pair with their ear buds. Video after the break.

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Become Very Unpopular Very Fast With This DIY EMP Generator

Taking a break from his book, “How to Gain Enemies and Encourage Hostility,” [FPS Weapons] shows us how to build our own handheld EMP generator which can be used to generate immediate dislike from anyone working on something electronic at the hackerspace.

The device is pretty simple. A DC source, in this case an 18650 lithium battery cell, sends power to an “Ultra High Voltage 1000kV Ignition Coil” (as the eBay listing calls it), when a button is pressed. A spark gap is used to dump a large amount of magic pixies into the coil all at once, which generates a strong enough magnetic pulse to induce an unexpected voltage inside of a piece of digital electronics. This usually manages to fire a reset pin or something equivalent, disrupting the device’s normal operation.

While you’re not likely to actually damage anything in a dramatic way with this little EMP, it can still interrupt an important memory write or radio signal and damage it that way. It’s a great way to get the absolute shock of your life if you’re not careful. Either from the HVDC converter or the FCC fines. Video after the break.

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WTF is Degaussing?

The modern office has become a sea of LCD monitors. It’s hard to believe that only a few years ago we were sitting behind Cathode Ray Tubes (CRTs). People have already forgotten the heat, the dust, and the lovely high frequency squeal from their flyback transformers.

Image by Søren Peo Pedersen via wikipedia
Image by Søren Peo Pedersen via wikipedia

There was one feature of those old monitors which seems to be poorly understood. The lowly degauss button. On some monitors it was a physical button. On others, it was a magnet icon on the On Screen Display (OSD). Pressing it rewarded the user with around 5 seconds of a wavy display accompanied by a loud hum.

But what exactly did this button do? It seems that many never knew the purpose of that silly little button, beyond the light-and-sound show. The truth is that degaussing is rather important. Not only to CRTs, but in many other electronic and industrial applications.


Of Shadow Masks and Aperture Grilles

Close up of a shadow mask by Rauenstein via Wikipedia
Close up of a shadow mask by Rauenstein via Wikipedia

A CRT has quite a few components. There are three electron guns as well as steering and convergence coils at the rear (yoke) of the tube. The front of the tube has a phosphor-coated glass plate which forms the screen. Just behind that glass is a metal grid called the shadow mask. If you had enough money for a Sony screen, the shadow mask was replaced by the famous Trinitron aperture grille, a fine mesh of wires which performed a similar function. The shadow mask or aperture grille’s  job is to ensure that the right beams of electrons hit the red, green, or blue phosphor coatings on the front of the screen.

This all required a very precise alignment. Any stray magnetic fields imprinted on the mask would cause the electron beams to bend as they flew through the tube. Too strong a magnetic field, and your TV or monitor would start showing rainbows like something out of a 1960’s acid trip movie. Even the Earth’s own magnetic field could become imprinted on the shadow mask. Simply turning a TV from North to East could cause problems. The official term for it was “Color Purity”.

magnet-trickThese issues were well known from the early days of color TV sets. To combat this, manufacturers added a degaussing coil to their sets. A coil of wire wrapped around the front of the tube, just behind the bezel of the set. When the set was powered on, the coil would be fed with mains voltage. This is the well-known ‘fwoomp and buzz’ those old TV sets and monitors would make when you first turned them on. The 50 Hz or 60 Hz AC would create a strong moving magnetic field. This field would effectively erase the imprinted magnetic fields on the shadow mask or aperture grille.

Running high current through the thin degaussing coil would quickly lead to a fire. Sets avoided this by using a Positive Temperature Coefficient (PTC) thermistor in-line with the coil. The current itself (or a small heating coil) would heat up the PTC, causing resistance to increase, and current through the coil to drop. After about 5 seconds, the coil was completely shut down, and the screen was (hopefully) degaussed.

As time went on monitors became embedded systems. The PTC devices were replaced by transistors controlled by the monitor’s main microcontroller. Monitor manufacturers knew that their sets were higher resolution than the average TV set, and thus even more sensitive to magnetic fields. Users are also more likely to move a monitor while using it. This lead the manufacturers to add a degauss button to the front of their sets. A push of the button would energize the coil for a few seconds under software control. Some monitors would also limit the number of times a user could push the button, ensuring the coil didn’t get too hot.

Holding a magnet near the front of a black and white (or a monochrome ‘green screen’) CRT created visible distortion, but no lasting damage. Mid-century hackers who tried the same trick with their first color TV quickly learned that the rainbow effect stayed long after the magnet was moved away. In extreme cases like these, the internal degaussing coil wouldn’t be strong enough to clear the shadow mask.

Commercial degaussing coil
Commercial degaussing coil

When all else failed, a handheld degaussing coil or wand could be used. Literally waving the magic wand in front of the screen would usually clear things up. It was of course possible to permanently damage the shadow mask. Back in 2007, I was working for a radar company which had been slow to switch to LCD monitors. Being a radar shop, we had a few strong magnetron magnets lying around. One of these magnets was passed around among the engineers. Leaving the magnet under your monitor overnight would guarantee rainbows in the morning, and a shiny new LCD within a few days.

Queen Mary, showing her degaussing coil

CRTs aren’t the only devices which use degaussing coils. The term was originally coined in 1945 by Charles F. Goodeve of the Royal Canadian Naval Volunteer Reserve (RCNVR). German mines were capable of detecting the magnetic fields in a naval ship’s steel hull. Coils were used to mask this field. The Queen Mary is one of the more famous ships fitted with a degaussing coil to avoid the deadly mines.

Even mechanical wristwatches can benefit from a bit of degaussing. A watch which has been magnetized will typically run fast. Typically this is due to the steel balance spring becoming a weak magnet. The coils of the spring stick together as the balance wheel winds and unwinds each second. A degaussing coil (or in this case, more properly a demagnetizer) can quickly eliminate the problem.

A story on degaussing wouldn’t be complete without mentioning magnetic media. Handheld or tabletop degaussing coils can be used to bulk erase floppy disks, magnetic tape, even hard disks. One has to wonder if the degaussing coils in monitors were responsible for floppy disks becoming corrupted back in the old days.

So there you have it. The magic degaussing button demystified!

Analog Clocks Play Their Own Beat

Play the demo video below and try not to let the rhythm worm its way into your brain. What you’re hearing is the sound of a bunch of clocks, amplified. None of them are keeping wall time, but all of them are playing together.

[Gijs] makes crazy musical instruments. He doesn’t give us much more than a video and a couple schematics for this project, so this one’s still a bit of an enigma, but here’s what we’ve put together.

Klok slave unit schematic
Klok slave unit schematic

The video looks like eight identical version of the same module. The input takes a voltage and converts the rising and falling edges into pulses to drive the coil of an el-cheapo clock. The LEDs pulse as the poles of the clock switch to the incoming beats. The output comes from an amplified piezo sensor stuck on the back of each clock. That is, what you’re hearing is each clock ticking, but amplified. And if you watch the dials spin, it doesn’t look like any of them are telling time.

So far so good, and it matches up with the schematic. But what’s up with that switch on the front? It doesn’t show up anywhere.

And what’s driving the show? [Gijs] tantalizes us with a master clock module (on the same page) that looks like it does keep time, and outputs subdivisions thereof. But that would be too slow to be what’s used in the video. Has he swapped the crystal to make it run faster? It’s a mystery.

Of course, we’d expect no less from the man who mics up a kitchen timer or a gear motor and adds them to his synthesizer rack. We’ve covered a bunch more of [Gijs]’s work in the past, from his video mixers to this hard-drive turned synth oscillator, but this time he’s got us scratching our heads a bit, as well as tapping our feet.

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Retrotechtacular: Step Up and Get Your Transformer Training

Whether you’re just getting into electronics or could use a refresher on some component or phenomenon, it’s hard to beat the training films made by the U.S. military. This 1965 overview of transformers and their operations is another great example of clear and concise instruction, this time by the Air Force.

It opens to a sweeping orchestral piece reminiscent of the I Love Lucy theme. A lone instructor introduces the idea of transformers, their principles, and their applications in what seems to be a single take. We learn that transformers can increase or reduce voltage, stepping it up or down through electromagnetic induction. He moves on to describe transformer action, whereby voltages are increased or decreased depending on the ratio of turns in the primary winding to that of the secondary winding.

He explains that transformer action does not change the energy involved. Whether the turns ratio is 1:2 or 1:10, power remains the same from the primary to the secondary winding. After touching briefly on the coefficient of coupling, he discusses four types of transformers: power, audio, RF, and autotransformers.

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