Solid State Tesla Coil Plays Music

If you’ve ever wanted to build a Tesla coil but found them to be prohibitively expensive and/or complicated, look no further! [Richard] has built a solid-state Tesla coil that has a minimum of parts and is relatively easy to build as well.

This Tesla coil is built around an air-core transformer that steps a low DC voltage up to a very high AC voltage. The core can be hand-wound or purchased as a unit. The drive circuit is where this Tesla coil built is set apart from the others. A Tesla coil generally makes use of a spark gap, but [Richard] is using the Power Pulse Modulator PWM-OCXi v2 which does the switching with transistors instead. The Tesla coil will function with one drive circuit but [Richard] notes that it is more stable with two.

The build doesn’t stop with the solid-state circuitry, though. [Richard] used an Arduino with software normally used to drive a speaker to get his Tesla coil to play music. Be sure to check out the video after the break. If you’re looking for a Tesla coil that is more Halloween-appropriate, you can take a look at this Tesla coil that shocks pumpkins!

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High Altitude Balloon Keeps Going

Here’s a post from the AMSAT-UK high altitude balloon blog. It’s a great story about a balloon cruising at about 12km above the Earth completing its sixth circumnavigation of the planet. That post is from October 4th, and two weeks later the balloon is still going strong. Right now it’s over the Baltic heading into Russia with no sign of stopping or popping any time soon.

globeThe balloon was launched July 12, 2014 from Silverstone, UK. In the 100 days since then, this balloon has covered 144168 kilometers and has crossed its launching longitude six times. Even if this balloon weren’t trapped at high latitudes (including coming within 9 km of the pole), this balloon has still travelled more than three times the equatorial circumference of the Earth.

The balloon was built by [Leo Bodnar] a.k.a. [M0XER] with a self-made plastic foil envelope. The solar-powered payload weighs only 11 grams. It’s an exceptional accomplishment and one that has smashed all the amateur high altitude balloon distance records we can find.

Creating a 2D Film with 3D Printed Frames

In the early days of film, there was a time when French 3D Cinema was called “Relief Cinema”. The word, Relief, however brings the idea of something physical to mind when we hear it, which is why the name was later tweaked to include the more intangible term, 3D. Playing on this fact, French Artist [Julien Maire] has designed and built an over-sized projector for his installation titled “Relief“, that creates an animation by passing light through a series of individual 3D vignettes.

[Julien’s] intricately built projection reel in itself is an impressive mechanical feat, arguably out-staging the image it exists to produce on the wall of the gallery space. The eighty-five individual frames that create the short clip of a man digging a hole in the ground, consist of small figurines made with a stereo lithography printer. The semi-transparent nature of the resin used by the SLA printer gives the shadow cast by the projector a series of foggy-values that create a three dimensional appearance instead of merely casting a silhouette of the shape. This installation blends new and old technologies together to produce something we’re familiar with, but leaves us admiring an object that we’ve never seen before.


[Julien’s] “Relief” is currently being exhibited at iMAL (interactive Media Art Laboratory in Brussels) which will run throughout the month of October. If you happen to find yourself on a long stay in Europe before the Hardware Workshop in Munich, you could make a pitstop and check it out!

Open-Source Water Quality Tester

Contaminated water is a huge problem in many third-world countries. Impure water leads to many serious health problems, especially in children. Installing a water purification system seems like a simple solution to this problem, but choosing the right purification system depends on the level of contaminants in the water.

Water turbidity testers are often used to measure the severity of water contamination. Unfortunately most commercial water turbidity testers are very expensive, so [Wijnen, Anzalone, and Pearce] set out to develop a much more affordable open-source tester. Their tester performs just as well as commercial units, but costs 7-15 times less.

The open-source water tester was designed in OpenSCAD and 3d printed. It houses an Arduino with a custom shield that measures the frequency from several TSL235R light-to-frequency converters. An LED illuminates the water and the sensors measure how much light is diffused and reflected off of particles in the water. Another sensor measures the brightness of the LED as a baseline reference. The turbidity of the water is calculated from the brightness values, and is displayed on a character LCD. More details about the tester are included in a fairly extensive paper.

[Thanks Andrew]

Microbial Fuel Cell with a Side of Betta Fish

Move over, potato batteries: DIY microbial fuel cells are here to stay! A microbial fuel cell (MFC) is a device that uses bacteria in an anaerobic (oxygen-poor) environment to convert chemical energy into electricity. [drdan152] posted steps on how to make a soil-based MFC  with a neat twist: it’s also a fishbowl for a betta fish.

[drdan152] used soil from the wetlands, referred to as “muck.” This nutrient-rich soil provided a hearty supply of bacteria, especially Geobacter species, known for their uncanny ability to transport electrons outside their cells using bacterial nanowires. The proton exchange membrane (PEM) was made up of salt, water, and agar. After some initial runs, [drdan152] determined that flat char cloth made the best anode, while red copper wire served as the cathode. Assembling the MFC was as simple as surrounding the anode with a thick layer of muck on all sides, adding the PEM on top, followed by water. The cathode was situated halfway out of the water.

After a couple of days, the voltage increased in proportion to the amount of bacteria growing on the anode. The betta fish can happily live in this habitat for a short period of time(it still has to be fed, of course), and the bacteria certainly won’t mind – the fish’s excrement provides an additional food supply. As a bonus, the water is kept clean. However, like any aquarium, the water will need to be changed periodically as carbon dioxide byproduct accumulates from the fish’s respiration and the MFC (high carbon dioxide levels = dead betta fish).

The MFC generates 725 mV. [drdan152] is not satisfied with that number, and is testing out charge pump circuits to generate as much as 3V. We are looking forward to seeing the results. We also wonder if a small aquatic plant could help make it a more self-sustaining environment for the fish. In the meantime, [drdan152] is encouraging others to try larger-scale versions of this MFC. Perhaps MFC-powered carnivorous robots doubling as mobile aquariums are in our near future.

The Joys Of Shipping From China

A few months ago, news of a new PCB fab service headed up by [Ian] over at Dangerous Prototypes leaked onto the Internet. It’s extremely cheap – $14 USD for a 5cm square board with free worldwide shipping. [Ian] admits the boards aren’t the greatest quality, that’s not the point; the site’s motto is simply, ‘No bull, just crappy PCBs.’

What began as an internal website to handle all of DP’s PCB orders was now on the Internet, and orders were flying in. At first, shipping a few dozen PCBs around the globe every week was easy, but since Dirty PCBs hit the big time, customers rightfully or not, started freaking out because of the oddities of Chinese shipping and logistics companies.

[Ian] is using Espeed Post for all their shipping, and if you’ve ever ordered anything from China off of Ebay, it’s possible you’ve had something shipped through Espeed before. Because of the oddities of shipping, and the fact that Shenzhen and Hong Kong are right next to each other, even the people at Dangerous Prototypes don’t know which countries your PCBs will go through on the trip from the fab house to your front door. This has caused much consternation with DirtyPCB customers that don’t seem to realize they’re getting custom PCBs for under two dollars a board, shipped to them across the world in a week for free. Some people’s children, huh?

Things get significantly, ahem, dirtier, when Chinese holidays are taken into account. China has a lot of them, and they’re long. They’re just wrapping up the National Day holiday, 10 days in the first week of October. Everyone is backlogged, and the China/Hong Kong border is the mess of trucks seen above.

If a holiday isn’t bad enough, the new President of China is cracking down on corruption. 500 officials were fired at the largest land border with Hong Kong, due in no small part to vans full of meth and tons of counterfeit currency. Every package leaving China is inspected individually, and shipping times have exploded.

To deal with this, Dangerous Prototypes has posted a big red warning on the dirtypcb site, but experience in dealing with people on the Internet tells them this won’t be a viable solution. They’re now dealing directly with DHL, and are apparently getting priority clearance through customs. It’s not fun, as DP will now have to figure out how to work with DHL’s API. It’s a lot of work and a lot of trouble, but DP still has a few tricks up their sleeve – they’re working on an online schematic entry and PCB layout site and the extremely interesting DirtyCables – custom cables shipped to your door.

Remote Control for an Elevator


The elevator at [Alex]’s office building has some quirks which make it very inconvenient to everyone in the building. The major problem was that the doors of the elevator at each floor stay locked until someone walks down the hall to hit a button. Obviously this was a hassle, so [Alex] built a controller that can remotely call and unlock the elevator. (Part 2 of the project is located on a separate page.)

The first step was to source the hardware and figure out exactly how the controls for the elevator worked. [Alex] decided to use an Electric Imp for this project, and after getting it connected to the Internet, he realized that he could power it directly off of the elevator’s 10V supply. From there, he used relays to interface the Electric Imp with the “elevator call” and “elevator unlock” buttons inside the elevator’s control panel.

Once the hardware side was completed, it was time to move on to the software side. [Alex] wrote a mobile app for a user interface that can be accessed from anywhere, and also wrote the code for the Electric Imp agent and the code that runs on the Electric Imp itself. Now, a simple tap of a button on a mobile device is enough to call the elevator or unlock it, rather than in the past where someone had to run down a hall to hit the button.

We hope there is some security on the mobile app, otherwise anyone in the world will be able to call the elevator and turn it into a passenger-less useless machine!