Introduce Yourself To A PocketBeagle With BaconBits

March 14, 2018 by Roger Cheng 6 Comments

The PocketBeagle single-board computer is now a few months old, and growing fast like its biological namesake. An affordable and available offering in the field of embedded Linux computing, many of us picked one up as an impulse buy. For some, the sheer breadth of possibilities can be paralyzing. (“What do I do first?”) Perhaps a development board can serve as a starting point for training this young puppy? Enter the BaconBits cape.

When paired with a PocketBeagle, everything necessary to start learning embedded computing is on hand. It covers the simple basics of buttons for digital input, potentiometer for analog input, LEDs for visible output. Then grow beyond the basics with an accelerometer for I²C communication and 7-segment displays accessible via SPI. Those digging into system internals will appreciate the USB-to-serial bridge that connects to PocketBeagle’s serial console. This low-level communication will be required if any experimentation manages to (accidentally or deliberately) stop PocketBeagle’s standard USB network communication channels.

BaconBits were introduced in conjunction with the E-ALE (embedded apprentice Linux engineer) training program for use in hands-on modules. The inaugural E-ALE session at SCaLE 16X this past weekend had to deal with some last-minute hiccups, but the course material is informative and we’re confident it’ll be refined into a smooth operation in the near future. While paying for the class will receive built hardware and in-person tutorials to use it, all information – from instructor slides to the BaconBits design – is available on Github. Some of us will choose to learn by reading the slides, others will want their own BaconBits for independent experimentation. And of course E-ALE is not the only way to learn more about PocketBeagle. Whichever way people choose to go, the embedded Linux ecosystem will grow, and we like the sound of that!

RC Transmitter Hacked Into Music Player

March 14, 2018 by Tom Nardi 9 Comments

Packed with an incredible amount of hardware, and increasingly likely to be running an open source firmware, the modern RC transmitter is effectively a little multi-purpose computer in its own right. Accordingly there is a small, but growing, community of developers coming out with software applications targeting these switch-festooned wonders. It’s only a matter of time until they are running DOOM.

One such piece of software is TaraniTunes, developed by [GilDev]. This program allows you to load your OpenTX 2.2+ equipped Taranis Q X7 or Taranis X9D with music files which can be played on the transmitter’s built-in speaker. While it likely won’t win any awards for interface design, the large LCD display coupled with the radio’s numerous physical buttons and switches makes it relatively easy to navigate your music collection.

While the software [GilDev] has written for OpenTX looks straightforward enough, getting the songs on the radio is another story. For each track you need to merge the stereo channels into mono (as the transmitter only has a single speaker), and then convert it to a 32 kHz WAV. But don’t worry about the lack of ID3 tag information, TaraniTunes allows you to create a text file containing not only the filename of each track, but its name and artist.

We’ll admit this one should be filed away in the “Because I Can” category, but it’s still an impressive hack and a clever demonstration of the current state of RC transmitter technology.

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A Simple POV Business Card

March 9, 2018 by Jenny List 28 Comments

The business card is an odd survivor from the past, when you think about it. When a salesman in a Mad Men style suit stepped out of his Studebaker and walked past a room full of typists to the boss’s wood-paneled office, he would have handed over a card as a matter of course. It would get filed away in the Rolodex.

These days, making your card stand out from the crowd of print-shop specials has become an art form. In our community this extends to cards with integrated electronics, such as this one with a persistence-of-vision display driven by an ATtiny from [James Cochrane], shown in the video below. It’s by no means the first such card, but he takes us through its design and construction in great detail which makes the video below the break worth a look. If you have never made a toner transfer PCB for example, you can see how his was made.

He makes the point that while a POV spinner needs only to display in one direction, a card has to be waved back and forth. Thus it needs to change the direction of its display, and needs a tilt sensor to activate this. His construction method uses through-hole components, but is surface mount in that they are soldered to the top surface of the board. The result is a rather attractive POV card that maybe isn’t something you’d hand out to all and sundry, but perhaps that’s not the point.

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Adding Optics To A Consumer Thermal Camera

March 8, 2018 by Tom Nardi 16 Comments

[David Prutchi] writes in to tell us about his recent experiments with building lenses for thermal imaging cameras, which to his knowledge is a first (at least as far as DIY hardware is concerned). With his custom designed and built optics, he’s demonstrated the ability to not only zoom in on distant targets, but get up close and personal with small objects. He’s working with the Seek RevealPro, but the concept should work on hardware from other manufacturers as well.

In his detailed whitepaper, [David] starts by describing the types of lenses that are appropriate for thermal imaging. Glass doesn’t transmit the wavelengths that thermal camera is looking for, so the lenses need to be made of either germanium or zinc selenide. These aren’t exactly the kind of thing you can pick up at the local camera shop, and even small lenses made of these materials can cost hundreds of dollars. He suggests keeping an eye out on eBay for surplus optics you could pull them out of to keep costs down.

Creating the macro adapter is easy enough, you simply put a convex lens in front of the thermal camera. But telephoto is a bit more involved, and the rest of the whitepaper details the math and construction techniques used to assemble it the optics. [David] gives a complete bill of materials and cost breakdown for his telephoto converter, but prepare for a bout of sticker shock: the total cost with all new hardware is nearly $500 USD. The majority of that is for the special lenses though, so if you can score some on the second-hand market it can drop the cost significantly.

We’ve seen an impressive array of thermal camera hacks and projects recently, no doubt due to the falling prices of consumer-level imaging hardware. Given their utility as a diagnostic tool, a thermal camera might be something worth adding to your bag of tricks.

Desperately Trying To Find A Use For The ChugPlug

March 7, 2018 by Tom Nardi 21 Comments

[AkBKukU] writes in to tell us of his experiments with the rather vile-sounding “ChugPlug”, an odd portable AC power bank designed for the express purpose of powering MacBook chargers. It would seem more efficient to simply build a DC power bank with a MagSafe connector to cut out the charger all together, but presumably there is some market for this particular niche device. Especially at the $15 they are currently selling for on Amazon.

Unfortunately, the ChugPlug that [AkBKukU] bought doesn’t seem to work. After some experimenting he found that it appears to only be outputting 80 VAC, obviously too low for many devices to function. But he reasoned that some things, like switch mode power supplies or restive loads, might still work. He just needed to come up with a way to plug them into the ChugPlug.

If his testing setup gives you a case of sweaty palms, you aren’t alone. He breaks open a dead MacBook charger to recover the female AC connector, and then solders that directly to an AC grounding adapter. The resulting pigtail lets [AkBKukU] plug in various AC loads while allowing him to probe the wires with his multimeter and oscilloscope.

Once he’s satisfied his hack works conceptually, that is, he’s able to plug arbitrary AC loads into this purpose-built battery pack, he follows up with a less dangerous looking adapter. Making use of the shell of the dead MacBook charger and what some might describe as a salacious amount of hot glue, he produces a compact and relatively safe looking device that will let him use his handicapped ChugPlug as a general purpose source of AC power.

It’s not the most elaborate portable power supply we’ve ever seen, and certainly wouldn’t be our first choice in an emergency, but at least [AkBKukU] managed to wring some use out of the thing in the end.

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A Bit More Than A Microphone: The Electret Story

March 7, 2018 by Jenny List 35 Comments

When designing a microphone assembly the other day, I reached for an electret condenser microphone capsule without thinking. To be strictly accurate I ordered a pack of them, these small cylindrical microphones are of extremely high quality for their relatively tiny price.

It was only upon submitting the order that I had a thought for the first time in my life: Just what IS an electret condenser microphone?

A condenser microphone is easy enough to explain. It’s a capacitor formed from a very thin conductive sheet that functions as the diaphragm, mounted in front of another conductor, usually a piece of mesh. Sound waves cause the diaphragm to vibrate, and these vibrations change the capacitance between diaphragm and mesh.

If that capacitance is incorporated into an RC circuit with a very high impedance and a high voltage is applied, a near constant charge is placed upon it. Since the charge stays constant, changing the capacitance causes a tiny voltage fluctuation that can be retrieved as the audio signal from the microphone. Condenser microphones built in this way can be extremely high quality, but come at the expense of needing a high voltage power supply to supply the charge and an amplifier to buffer and magnify the audio.

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What’s Inside A Neonode Laser Sensor?

March 6, 2018 by Elliot Williams 16 Comments

Every once in a while, you get your hands on a cool piece of hardware, and of course, it’s your first instinct to open it up and see how it works, right? Maybe see if it can be coaxed into doing just a little bit more than it says on the box? And so it was last Wednesday, when I was at the Embedded World trade fair, and stumbled on a cool touch display floating apparently in mid-air.

The display itself was a sort of focused Pepper’s Ghost illusion, reflected off of an expensive mirror made by Aska3D. I don’t know much more — I didn’t get to bring home one of the fancy glass plates — but it looked pretty good. But this display was interactive: you could touch the floating 2D projection as if it were actually there, and the software would respond. What was doing the touch response in mid-air? I’m a sucker for sensors, so I started asking questions and left with a small box of prototype Neonode zForce AIR sensor sticks to take apart.

The zForce sensors are essentially an array of IR lasers and photodiodes with some lenses that limit their field of view. The IR light hits your finger and bounces back to the photodiodes on the bar. Because the photodiodes have a limited angle over which they respond, they can be used to triangulate the distance of the finger above the display. Scanning quickly among the IR lasers and noting which photodiodes receive a reflection can locate a few fingertips in a 2D space, which explained the interactive part of the floating display. With one of these sensors, you can add a 2D touch surface to anything. It’s like an invisible laser harp that can also sense distance.

The intended purpose is fingertip detection, and that’s what the firmware is good at, but it must also be the case that it could detect the shape of arbitrary (concave) objects within its range, and that was going to be my hack. I got 90% of the way there in one night, thanks to affordable tools and free software that every hardware hacker should have in their toolbox. So read on for the unfortunate destruction of nice hardware, a tour through some useful command-line hardware-hacking tools, and gratuitous creation of animations from sniffed SPI-like data pulled off of some test points.

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