Humidity Sensor Shootout

January 3, 2017 by 39 Comments

If you want to measure humidity (and temperature, and maybe even barometric pressure) in a device that you’re building, have a look at this comprehensive test of seven different options. We’re going to summarize the results here, but you’ll really want to read up on the testing methodology — it’s great science hacking. Did you know about using saturated salt solutions to produce constant humidity levels for calibration? We didn’t.

The eBay hacker favorite, the so-called DHT22 module, doesn’t fare all that well, with one of six that [Robert] tested being basically horrible, and three of them breaking within two years of use. The one that works well, however, is pretty good. Feeling lucky?

The Bosch BME280 looks great. It costs a bit more as a bare part, and a few times more than that when it is mounted on a friendly module, but it seems to be very reliable. And you get a barometer thrown in for the extra work. Indeed, it performed so well that Hackaday contributor [Nava Whiteford] put the part under a scanning electron microscope to figure out what’s going on.

The other sensors were fine, with the HTU21D and SHT71 being standouts for their ultra-fast response. For the full details, go click on that link at the top. Having just installed a sextet of DHT22s in our house last year, we’re left with that sinking feeling that we may have gotten what we paid for, which wasn’t much. At least they’re all still running.

Thanks to [Dodutils] and [mac012345] via comments in another thread.

Thermoacoustic Engine Has Only One Moving Part

January 3, 2017 by 19 Comments

Modern internal combustion engines have around 500 parts, with many of them moving in concert with the piston. But have you seen an engine with only one moving part, out of four in total? In the thermoacoustic engine, the power piston is the only part in motion. [YTEngineer] has built a very simple prototype that works on power provided by a tealight.

His little engine, slightly larger than a cigarette lighter, is composed of a test tube that serves as the cylinder, a smaller tube, called the choke, that fits inside the test tube, the stack, which is nothing more than some steel wool, and the power piston. [YTEnginer] nicely explains how the engine works: basically a temperature difference is used to induce high-amplitude sound waves that create the piston’s back-and-forth movement. The engine can be easily converted to an electricity generator by adding a magnet to the piston and a coil surrounding it.

The thermoacoustic engine is a particular type of Stirling engine. They have been proposed as electricity generators for space travel using radioisotopes as the heat source, among other applications. You may be interested in the history of Stirling engines, or perhaps even build a simple one.

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Junkyard Dish Mount Tracks Weather Satellites

January 2, 2017 by 11 Comments

There’s a magnificent constellation of spacecraft in orbit around Earth right now, many sending useful data back down to the surface in the clear, ready to be exploited. Trouble is, it often takes specialized equipment that can be a real budget buster. But with a well-stocked scrap bin, a few strategic eBay purchases, and a little elbow grease, a powered azimuth-elevation satellite dish mount can become affordable.

The satellites of interest for [devnulling]’s efforts are NOAA’s Polar-orbiting Operational Environmental Satellites (POES), a system of low-Earth orbit weather birds. [devnulling] is particularly interested in direct reception of high-definition images from the satellites’ L-band downlink. The mount he came up with to track satellites during lengthy downloads is a tour de force of junkyard build skills.

The azimuth axis rotates on a rear wheel bearing from a Chevy, the elevation axis uses cheap pillow blocks, and the frame is welded from scrap angle iron and tubing. A NEMA-23 stepper with 15:1 gearhead rotates the azimuth while a 36″ linear actuator takes care of elevation. The mount has yet to be tested in the wind; we worry that sail area presented by the dish might cause problems. Here’s hoping the mount is as stout as it seems, and we’ll look forward to a follow-up.

It would work for us, but a 4-foot dish slewing around in the back yard might not be everyone’s taste in lawn appurtenances. If that’s you and you still want to get your weather data right from the source, try using an SDR dongle and chunk of wire.

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Lost PLA Casting Brings Out The Beauty Of Macromolecules

January 2, 2017 by 6 Comments

Biochemistry texts are loaded with images of the proteins, nucleic acids, and other biopolymers that make up life. Depictions of the 3D structure of macromolecules based on crystallography and models of their most favorable thermodynamic conformations are important tools. And some are just plain beautiful, which is why artist [Mike Tyka] has taken to using lost-PLA casting to create sculptures of macromolecules from bronze, copper, and glass.

We normally don’t cover strictly artistic projects here at Hackaday, although we do make exceptions, such as when the art makes a commentary on technology’s place in society. In [Mike]’s case, not only is his art beautiful and dripping with nerd street cred, but his techniques can be translated to other less artsy projects.

kcsa_5_bigFor “Tears”, his sculpture of the enzyme lysozyme shown in the banner image, [Mike] started with crystallographic data that pinpoints every peptide residue in the protein. A model is created for the 3D printer, with careful attention paid to how the finished print can be split apart to allow casting. Clear PLA filament is used for the positive because it burns out of the mold better than colored plastic. The prints are solvent smoothed, sprues and air vents added, and the positive is coated with a plaster mix appropriate for the sculpture medium before the plastic is melted out and the mold is ready for casting.

[Mike]’s sculpture page is well worth a look even if you have no interest in macromolecules or casting techniques. And if you ever think you’ll want to start lost-PLA casting, be sure to look over his build logs for plenty of tips and tricks. “Tears” is executed in bronze and glass, and [Mike]’s description is full of advice on how to handle casting such vastly different media.

Thanks to [Dave Z.] for the tip.

Atari Now Runs Java, Thankfully Doesn’t Require Constant Updates

January 2, 2017 by 24 Comments

Java Grinder is a tool that compiles Java programs to run on platforms like microcontrollers and consoles, by outputting native assembly code and using APIs to work with custom hardware like bespoke graphics and sound chips. Amongst other hardware, Java Grinder supports the Commodore 64, which uses a variant of the 6502 CPU. [Michael Kohn] realized the Atari 2600 shares this processor, and figured he’d get started on making Java Grinder work with the Atari by expanding on the C64 work done by [Joe Davisson]. Together, they brought Java to the Atari 2600 and made a game along the way.

According to [Michael], parts of the project were easy, as some Java routines compile down into as little as 1 or 2 instructions on the 6502. Other parts were harder, like dealing with the graphics subsystem, and modifying Java Grinder to output 8-bit bytecode to fit into the Atari’s tiny 4K ROM limit. Even with this tweak, they still couldn’t fit in a game and title screen. In the end they relied on bank switching to get the job done. [Joe]’s game is pretty solid fare for the Atari 2600 — blocky graphics and bleepy sounds — and they’ve uploaded it to the page so you can try it yourself in an emulator.

At the end of the day, porting Java code to a system with 128 bytes of RAM probably isn’t going to be particularly useful. However, as a coding exercise and learning experience, there’s a lot of value here in terms of building your skills as a coder. Other such experiments have shown us Java running on other unexpected devices, like the Sega Genesis or the MSP430. Video after the break.

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Gravity Simulations With An FPGA

January 2, 2017 by 25 Comments

Gravity can be a difficult thing to simulate effectively on a traditional CPU. The amount of calculation required increases exponentially with the number of particles in the simulation. This is an application perfect for parallel processing.

For their final project in ECE5760 at Cornell, [Mark Eiding] and [Brian Curless] decided to use an FPGA to rapidly process gravitational calculations. This allows them to simulate a thousand particles at up to 10 frames per second. With every particle having an attraction to every other, this works out to an astonishing 1 million inverse-square calculations per frame!

The team used an Altera DE2-115 development board to build the project. General operation is run by a Nios II processor, which handles the VGA display, loads initial conditions and controls memory. The FPGA is used as an accelerator for the gravity calculations, and lends the additional benefit of requiring less memory access operations as it runs all operations in parallel.

This project is a great example of how FPGAs can be used to create serious processing muscle for massively parallel tasks. Check out this great article on sorting with FPGAs that delves deeper into the subject. Video after the break.

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A Singing Arc Lighter

January 2, 2017 by 54 Comments

We’ve all been guilty of buying things we want, but don’t need. And that’s how [PodeCoet] found himself in possession of a couple of double-arc electric lighters, thanks to those far-eastern websites purveying cheap goods. ‘Tis the season of giving after all, justified [PodeCoet]. Being a hacker, the obvious thing to do was to make them belt out tinny tunes. If you’re still holding on to your gas lighters, don’t — because these electric ones are ‘oh so hackable’. Dual-arcs are the same, but twice the fun.

[PodeCoet] starts off with a tear down of the lighter, to figure out the schematic and understand how it works. There’s a charger IC for the LiPo, an unidentifiable micro-controller, a pair of FET’s driving a pair of power transistors, which in turn drive the HF output transformer at around 15.6kHz. He guesses that the “original micro-controller is probably an OTP part like a 12C508” but in the absence of a chipID he couldn’t be sure.

Instead of trying to break his head over it, he just swapped in a pin-compatible PIC12F1840. All that’s left to do is to write some quick-n-dirty code and sprinkle it with funny comments in order to modulate the output signal at audio frequencies. His first choice of tune was “We are Number One” by Lazy Town, the Icelandic educational musical comedy children’s television series (phew). But redditors are awesome, and someone asked him to add the “Imperial March” and [PodeCoet] obliged.

Since he was going to gift these lighters, the sneaky hacker added a prank in the code. Every time the button is pressed for more than two seconds, it works as normally expected and a counter is incremented. On the 20th count, and for one time only, the tune is played. No amount of pressing the button will play the tune again, confounding the user to wonder if he was hallucinating. This also helps ensure the lighter does not self-destruct prematurely, since the output transformer is likely designed for low duty cycles. His blog post contains all of the information needed to do this hack along with handy tips to avoid the problems he faced. A “Happy Birthday” tune would be great when lighting some birthday candles, we think.

[PodeCoet] has a fancy for high voltage stuff – check out “Home built Stun Baton turns you into a cop from Demolition Man“. This man surely loves his pranks, as evidenced by “Hacking your Co-Workers Label Makers“. And the farce is strong in this one — “Student trolls anti-Arduino Prof with parasite MCU“.

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