A Simple LED Flashlight Composed of a Relay and a Magnet

In our tips line we sometimes receive hacks that are amazing just because of their ingenuity. This relay-powered flashlight is definitely one of them. It has been named RattleGen by its creator [Berto], who apparently often makes simple hacks used in his everyday life (have a look at his YouTube channel).

To understand this hack, you first need to know (in case you didn’t already) that a magnet moving near a conductor (here a coil) induces a voltage at its terminals. This is called electromagnetic induction. In the picture you see above, you may distinguish a disassembled relay with a magnet located on the lever’s end. As a ferromagnetic metal is already placed inside the coil, the lever is by default ‘stuck’ in this position. By continuously pressing the latter on its other end, important voltage spikes are created at the coils terminals. [Berto] therefore used a bridge rectifier to transform the AC into DC, and a 1000uF capacitor to smooth the power sent to his super bright LED. A video of the system in action is embedded after the break.

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Making a Power Inductor Checker

inductor-checker-for-oscilloscope

Back to the basics: there are three kinds of passive electronic components: Inductors, Capacitors and Resistors. An inductor can be easily built and many types of core and bobbin kits are available. However, characterizing one hypothetical coil you just made is quite tricky as its inductance will depend on the measurement frequency and DC bias current. That’s why [ChaN] designed the circuit shown above.

As you may guess, RF enthusiasts are more interested in the inductance vs frequency curve while power circuit designers prefer inductance vs load current (for a given frequency). The basic principle behind the circuit shown above is to load an inductor for repetitive short periods and visualizing the current curve with an oscilloscope connected to a sense resistor. When loading the inductor, the current curve will be composed of two consecutive slopes as at a given moment the coil’s core will be saturated. Measuring the slope coefficient then allows us to compute the corresponding inductance.

[Via Dangerous Prototypes]

Building a linear motor

linear-motor

We admit that this project doesn’t have very many details available, but it was just too neat for us to pass up. It’s a small linear motor which [ligonapProduktion] built after seeing a very brief description of a commercially available version.

The video after the break shows him testing the motor. In this screenshot he’s holding the center shaft while the coil assembly moves back and forth. But it works with a stationary coil moving the rod as well. The motor is basically a modified solenoid. There are sixteen neodymium magnets inside the shaft. The set of four coils is driven by an ATtiny44. Just like a stepper motor, energizing the coils in the correct order pushes against the rare earth magnets creating motion.

We’re not sure if he has any use in mind for this build. For us we just like to see the concept in practice (we feel the same way about a homopolar motor build).

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[Staci Elaan]‘s awesome portable tesla coils.

We stumbled onto [Staci's] videos a while ago when we posted this big tesla gun. While it wasn’t the first portable coil we had seen, it was certainly an impressive implementation. In the comments we found [Staci] had already been making these for a while. Hers were big and small, had awesome modulation, and looked freaking cool too.

It also should be pointed out that [Staci] donates her coils to people when she’s done! Let me say that again, she gives them away to groups of people that could use them. That deserves some respect.

Unfortunately, [Staci] didn’t document her builds in great detail at the time. She has added some information recently though.   You can read about her first working prototype from 2006, or a slightly more modern one here.

Of course, the real fun is in seeing them work.

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Coil gun with parts pulled from an electric stapler

[Lou's] latest tutorial details the process of turning an electric stapler into a coil gun. The stapler is the expensive part, but the rest is pretty simple. He used PVC pipe and a handful of fittings along with a few supplies you probably have kicking around your shop.

It’s surprising how perfect the Bostitch stapler (from which the parts were pulled) is for this project. The mechanism that drives the staples into your pages uses a solenoid with a rather large coil. To turn it into a coil gun you simply need to replace the core of the solenoid with a metal projectile. In the video after the break [Lou] shows us how to make a barrel onto which the coil can be mounted. From there he uses a wooden spacer to position a hunk of smooth metal from a bolt which serves as the projectile. The stapler’s original drive circuitry and trigger mechanism do the rest.

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Wireless iPod charger built from scratch

Despite the obvious use of a lot of wire, this project is actually a wireless charging system. [Jared] built it as a way to explore the concepts behind transferring power inductively. Alternating current on one of the white coils induces current on the other. This is then rectified, and regulated for use as a 5V charger. In this case it powers his iPod, but any USB device should work with the setup.

The transmitter uses the power supply from an old laptop as a source. Some filtering and a couple of MOSFETS are responsible for generating the AC current on the transmitting coil. The receiving coil feeds the bridge rectifier. In the writeup that voltage is fed to a 7805 regulator to provide a stable 5V output. However, in the video demo after the break [Jared] shows off the boost converter that he uses on his improved circuit. This way if the voltage drops due to poor alignment of the coils it will still be able to provide a steady output.

We’ve seen the same coil concept used to add wireless charging to cellphones too.

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Tutorial series shows you everything you need to salvage transformers from microwaves

mot-salvaging

Transformers certainly have a tendency to increase the cost of any project, especially if you need a large transformer to get the job done. Microwave ovens are great sources of free transformers, though they are not always in the shape required for your next build.

[Matt] put together three great tutorial videos covering the basics of salvaging Microwave Oven Transformers (MOTs), that anyone new to the process should watch before giving it a go. The first video covers MOT removal and disassembly, which is a time consuming yet easy process providing you follow [Matt’s] pointers.

The second video delves into transformer theory, and discusses how to achieve optimal performance when rebuilding an MOT or hand wrapping coils to fit your project specs. The third video in the series follows [Matt] as he rebuilds one of the salvaged transformers, documenting his pitfalls and successes along the way.

If you haven’t given much thought to salvaging MOTs, we definitely recommend taking a bit of time to watch the video series in full – it’s definitely worth it.

You can see the first video in the series after the jump – the rest can be found via the YouTube link above.

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