Better Capacitors Through Nanotechnology

Traditionally, capacitors are like really bad rechargeable batteries. Supercapacitors changed that, making it practical to use a fast-charging capacitor in place of rechargeable batteries. However, supercapacitors work in a different way than conventional (dielectric) capacitors. They use either an electrostatic scheme to achieve very close separation of charge (as little as 0.3 nanometers) or electrochemical pseudocapacitance (or sometime a combination of those methods).

In a conventional capacitor the two electrodes are as close together as practical and as large as practical because the capacitance goes up with surface area and down with distance between the plates. Unfortunately, for high-performance energy storage, capacitors (of the conventional kind) have a problem: you can get high capacitance or high breakdown voltage, but not both. That’s intuitive since getting the plates closer makes for higher capacitance but also makes the dielectric more likely to break down as the electric field inside the capacitor becomes higher with both voltage and closer plate spacing (the electric field, E, is equal to the voltage divided by the plate spacing).

[Guowen Meng] and others from several Chinese and US universities recently published a paper in the journal Science Advances that offers a way around this problem. By using a 3D carbon nanotube electrode, they can improve a dielectric capacitor to perform nearly as well as a supercapacitor (they are claiming 2Wh/kg energy density in their device).

cap1The capacitor forms in a nanoporous membrane of anodic aluminum oxide. The pores do not go all the way through, but stop short, forming a barrier layer at the bottom of each pore. Some of the pores go through the material in one direction, and the rest go through in the other direction. The researchers deposited nanotubes in the pores and these tubes form the plates of the capacitor (see picture, right). The result is a capacitor with a high-capacity (due to the large surface area) but with an enhanced breakdown voltage thanks to the uniform pore walls.

cap2To improve performance, the pores in the aluminum oxide are formed so that one large pore pointing in one direction is surrounded by six smaller pores going in the other direction (see picture to left). In this configuration, the capacitance in a 1 micron thick membrane could be as high as 9.8 microfarads per square centimeter.

For comparison, most high-value conventional capacitors are electrolytic and use two different plates: a plate of metallic foil and a semi-liquid electrolyte.  You can even make one of these at home, if you are so inclined (see video below).

We’ve talked about supercapacitors before (even homebrew ones), and this technology could make high capacitance devices even better. We’ve also talked about graphene supercaps you can build yourself with a DVD burner.

It is amazing to think how a new technology like carbon nanotubes can make something as old and simple as a capacitor better. You have to wonder what other improvements will come as we understand these new materials even better.

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Broken Finger Is No Obstacle to Modern Hacker

[Jim Merullo] and his son were enjoying a nice game of Frisbee when an unfortunate dive led to an injury. His son broke his pinky finger leaving doctors no choice other than bounding his entire left hand in an unreasonably large cast. For most, this would mean no use of the left hand for several weeks, which is somewhat problematic if tin01your son has a Minecraft addiction.  [Jim], however, is no stranger to the hacker community and began working on a solution. He broke out the #2 Philips screwdriver, fired up the soldering iron and got to work.

A detailed analysis of the injured left hand revealed limited use of the middle and ring finger, and full use of the thumb. Because his son played the game using his right hand for the mouse and left for the keyboard, he needed to find a way for him to operate a keyboard with the limited use of his left hand. He took apart an old USB keyboard and soldered up some tactile switches to emulate the needed key presses. After making a fashionable Altoids tin mount that fit over the cast, his son was able to enjoy his favorite video game with limited interruption.

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Hackaday Links: October 25, 2015

There are dozens of different 3D printable cases out there for the Raspberry Pi, but the BeagleBone Black, as useful as it is, doesn’t have as many options. The folks at 3D hubs thought they could solve this with a portable electronics lab for the BBB. It opens like a book, fits a half-size breadboard inside, and looks very cool.

The guy who 3D printed his lawnmower has a very, very large 3D printer. He now added a hammock to it, just so he could hang out during the very long prints.

There’s a box somewhere in your attic, basement, or garage filled with IDE cables. Wouldn’t they be useful for projects? Yep, only not all the wires work; some are grounds tied together, some are not wired straight through, and some are missing. [esot.eric] has the definitive guide for 80-wire IDE cables.

Like case mods? Here’s a golden apple, made out of walnut. Yes, there are better woods he could have used. It’s a wooden replica of a Mac 128 with a Mac Mini and LCD stuffed inside. Want a video? Here you go.

If you have a 3D printer, you’re probably familiar with PEEK. It’s the plastic used as a thermal break in non-all-metal hotends. Now it’s a filament. An extraordinarily expensive filament at €900 per kilogram. Printing temperature is 370°C, so you’ll need an all-metal hotend.

It’s the Kickstarter that just keeps going and going and going. That’s not a bad thing, though: there really isn’t much of a market for new Amiga 1200 cases. We’ve featured this project before, but the last time was unsuccessful. Now, with seven days left and just over $14k to go, it might make it this time.

DIY Powder Coating

If you don’t yet have a toaster oven you can’t use with food, here’s yet another reason: DIY powder coating. Powder coating is much harder and more durable than paint – a property imbued to it by the fact that it’s baked on to a part. [Thomas] had a go at powder coating some skateboard trucks, and with the right tools, found the process downright easy.

[Thomas] only needed a few things to powder coat his parts, the first and most important being a powder coat gun. A few years ago, Craftsman produced a powder coat gun that’s still available on Amazon and eBay for about $50. Powders are plentiful and cheap in small quantities. The only other tools needed were an N95 or better respirator, some high temperature tape for masking off the part and a toaster oven. If you want to coat big parts, there are DIY oven options for that.

After the part was sandblasted down to bare metal, [Thomas] masked off all the holes and threads of the part with polyimide tape. Any tape that’s capable of withstanding high temperatures will do, and most of us have a roll of Kapton sitting next to a 3D printer, anyway.

The part is coated with powder via an electrostatic charge, and this means attaching a ground lead from the gun to the part. After that, it’s just filling the gun with powder, putting it in the oven set at 450°F, and letting the powder liquefy.

In the video below, you can see [Thomas] sandblasting, powdering, and baking a set of aluminum skateboard trucks using his method. Compared to other methods of finishing metal parts – anodizing or plating, for instance, powder coating is remarkably easy and something anyone can do in a garage.

Thanks [Tyler] for sending this one in.

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Raspberry Pi Sense HAT Super Weather Dashboard

[InitialState] posted a great multipart tutorial about building what he calls a “Hyper-local Weather Dashboard.” In plain language, he created a Raspberry Pi-based web page that fuses weather data from Wunderground along with locally sensed weather data.

The tutorial has thee parts. The first part covers reading data from Wunderground using their developer’s API (you’ll need an API key; a free one is good for 500 queries a day). The second part covers using the Pi Sense HAT to measure local temperature, humidity, and pressure. The final part ties it all together using producing the hyper-local weather dashboard (whatever that really means).

We talked about the Sensor HAT earlier (and there’s more info in the video, below). Seems like those lights could do something, although that wouldn’t do you any good over a web interface. This is a good-looking project (and tutorial) and easy enough that it would be a good place to start
experimenting with the Raspberry Pi.

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Fitting 3D Prints On Eagle Boards

One of the hardest things you’ll ever do is mesh your electronic design with a mechanical design. Getting holes for switches in the right place is a pain, and if you do it enough, you’ll realize the beauty of panel mount jacks. This is especially true when using Eagle to design a PCB, but with a few tricks, it’s possible to build 3D printable pieces directly from Eagle designs.

[Tyler] built a clock with a bunch of LEDs. While the clock worked great, there was a lot of light leakage around the segments of his custom seven-segment numbers. The solution is a light mask, and [Tyler] figured out how to make one in Eagle.

The first step is to draw a new layer on the Eagle board that defines the light mask. This is exported as an EPS file in the CAM processor that gives him a 2D drawing. At least it’s to scale.

The next step is to install Inkscape and install paths2openscad. This turns the two-dimensional drawing into a 2D object that can be rendered in OpenSCAD and exported as a 3D printable STL file.

Does the project work? The results are great – the entire light mask is a single-wall print, and since this light mask doesn’t need any mechanical strength, it should hold up well. The clock looks much better than before, and [Tyler] has a new technique for making 3D objects for his 2D PCBs.

An Improvised Synthetic Aperture Radar

[Henrik] is at it again. Another thoroughly detailed radar project has shown up on his blog. This time [Henrik] is making some significant improvements to his previous homemade radar with the addition of Synthetic Aperture Radar (SAR) to his previous Frequency Modulated Continuous Wave (FMCW) system.

[Henrik’s] new design uses an NXP LPC4320 which uniquely combines an ARM Cortex-M4 MCU along with a Cortex-M0 co-processor. The HackRF also uses this micro as it has some specific features that can be taken advantage of here like the Serial GPIO (SGPIO) which can be tediously configured and high-speed USB all for ~$8 in single quantity. The mixed signal design is done in two boards, a 4 layer RF board and 2 layer digital board.

Like the gentleman he is, [Henrik] has included schematics, board files, and his modified source from the HackRF project in his github repo. There is simply too much information in his post to attempt to summarize here, if you need instant gratification check out the pictures after the break.

The write-up on his personal blog is impressive and worth look if you didn’t catch our coverage of his single board Linux computer, or his previous radar design.

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