Making Lichtenberg Figures in Wood

Ever heard of a Lichtenberg Figure? It’s the branching electrical discharge you can sometimes see on an insulating material… That’s right — when the voltage is high enough — it’ll find a way. Using one of our favorite low-cost high voltage transformers from a microwave, [TheBackYardScientist] shows us how to make our own Lichtenberg Figures!

It’s actually pretty easy. All you need is an old microwave, some plywood, and water with baking soda mixed in. First, you’ll need to take the transformer out of the microwave — a simple hack we’ve covered many times before — you’ll need to wire it in a way that allows you to get a few thousand volts out of it.

Then by mixing baking soda in water, you can increase the conductivity — let the wood soak it up overnight, and now you’re ready to go! By attaching the leads to either side of the wood, it’s now conductive enough to allow the electricity to branch across the wood, burning awesome patterns as it goes — just take a look at the following video!

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Embed with Elliot: Interrupts, The Good…

What’s the biggest difference between writing code for your big computer and a microcontroller? OK, the memory and limited resources, sure. But we were thinking more about the need to directly interface with hardware. And for that purpose, one of the most useful, and naturally also dangerous, tools in your embedded toolchest is the interrupt.

Interrupts do exactly what it sounds like they do — they interrupt the normal flow of your program’s operation when something happens — and run another chunk of code (an interrupt service routine, or ISR) instead. When the ISR is done, the microcontroller picks up exactly where it left off in your main flow.

Say you’ve tied your microcontroller to an accelerometer, and that accelerometer has a “data ready” pin that is set high when it has a new sample ready to read. You can wire that pin to an input on the microcontroller that’s interrupt-capable, write an ISR to handle the accelerometer data, and configure the microcontroller’s interrupt system to run that code when the accelerometer has new data ready. And from then on everything accelerometer-related happens automagically! (In theory.)

This is the first part of a three-part series: Interrupts, the Good, the Bad, and the Ugly. In this column, we’ll focus on how interrupts work and how to get the most out of them: The Good. The second column will deal with the hazards of heavyweight interrupt routines, priority mismatches, and main loop starvation: the Bad side of interrupts. Finally, we’ll cover some of the downright tricky bugs that can crop up when using interrupts, mainly due to a failure of atomicity, that can result in logical failures and corrupted data; that’s certainly Ugly.

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Learn and Build a High Side Switch

As electronics engineer I have a mental collection of circuits that I’ve gathered over the years, much like a mechanic collects specialized tools as they work. All engineers do this and the tools in their tool boxes usually represent their project history and breadth.

A useful circuit to have in designer’s toolbox is the “high side switch”. Like it sounds, this is a circuit that switches the “high side” or positive voltage to a load.

We usually tend to switch things to ground as seen by outputs such as an Open Collector output, the reason being that ground usually is a known entity and is usually low impedance and is at a known voltage. But there are advantages to using a high-side switch in your circuits.

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How To Build a Pocket-Sized mBed Signal Generator

Last month, I talked about how to get started with mBed and ARM processors using a very inexpensive development board. I wanted to revisit mBed, though, and show something with a little more substance. In particular, I often have a need for a simple and portable waveform generator. It doesn’t have to be too fancy or meet the same specs as some of the lab gear I have, but it should be easy to carry, power off USB, and work by itself when required.

My requirements mean I needed a slightly more capable board. In particular, I picked up a K64F board. This is very similar to the KL25Z board but has a bit more of everything–speed, memory, etc. What I really wanted, though, was the SD card slot. I did, however, do my early testing on a KL25Z, so if you have one, you can still work through the code, although standalone operation won’t be possible. The price jumps from $13 to $35, but you get a lot more capability for the price.

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Tint your Epoxy Resin with Toner Powder

Epoxy resin is useful stuff. Whether for gluing stuff together or potting components, epoxy is a cheap and versatile polymer that finds its way into many hackish projects. But let’s face it – the stock color of most commercially available epoxies lacks a certain pizzazz. Luckily, [Rupert Hirst] at Tallman Labs shows us that epoxy is easily tinted with toner powder from a laser printer or copier.

Looking for a way to make his epoxy blend into a glue-up, [Rupert] also demonstrates that colored epoxy makes a professional looking potting compound. There’s just something about the silky, liquid look of a blob of cured black epoxy. [Rupert] harvested his toner powder from a depleted printer cartridge; only a smidgen is needed, so you should be able to recover plenty before recycling the cartridge. We’ve got to admit that seeing toner handled without gloves gives us the willies, though. And don’t forget that you can find cyan, magenta and yellow cartridges too if basic black isn’t your thing.

Sometimes it’s better to leave your epoxy somewhat clear, like when you’re potting an LED matrix for a pendant. But this neat trick might just spiff up your next project a bit.

[Thanks, Jake]

How to Build Anything Using Delrin and a Laser Cutter

Need a simple fab process to go from a humble vector graphic to a final part — in a matter of minutes? The CO2  laser cutter might be the right choice. As these tools open themselves up to widespread use through hackerspaces, I decided to give Delrin some well-deserved time under the spotlight.

The laser cutter yet-again proves itself a formidable tool with the construction of GameCube-Bot V2

This guide is a brief collection of tips and techniques that I’ve either learned from others or discovered on my own over the last couple years working with laser-cut Delrin (a.k.a Acetal) for functional prototypes. I hope this guide serves you well as we keep exploring the limits of the material.

As a disclaimer, keep in mind that in no way are these techniques unique or limited to Delrin. Many are not only years old but also common practice in either engineering design or the local machine shop. This article simply highlights the techniques shown here that perform both repeatably and predictably with Delrin and a couple hand-tools, and I hope to share them with a growing audience of laser cutter enthusiasts.

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Make Your Own Transparent Whiteboard

Now this is seriously cool. Beyond seeing it in movies, having a transparent whiteboard that lights the ink up is absolutely awesome and pretty darn unique. [Andrew McNeil] shows us how — and it’s pretty simple too!

As an avid YouTuber, [Andrew] often has to explain things by drawing out diagrams and what not. If you’ve ever tried to film yourself doing this, you’ll know it’s not easy. So what if you could use the whiteboard like you normally would? And that whiteboard is also the window of which you, the audience, watches through? It’s really quite brilliant, and already in use for some teaching methods.

But wait, are we talking about literally using a glass window to write on? Well… kind of. But the trick is to have the glass edge-lit using LEDs. Doing so will literally make your dry erase markers glow. It practically looks like a neon sign.

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