A Smart DIY Metal Detector

May 2, 2020 by Moritz v. Sivers 29 Comments

If you ever thought about becoming a treasure hunter this simple DIY metal detector by [mircemk] may be a nice project to start with.

The design is based on an opensource metal detector called Smart Hunter. This Very Low Frequency (VLF) metal detector uses transmitter and receiver coils in so-called Double-D geometry. The transmitter coil is driven by a signal generator module that operates at its resonant frequency of 4.74 kHz.

The resulting oscillating magnetic field will induce eddy currents in a nearby metal object that in turn induce a signal in the receiver coil. This signal is then fed into the microphone port of a smartphone and analyzed by a custom metal detector app. [mircemk] also included an audio amplifier and small speaker into the device.

The detector turned out to be quite sensitive and can detect a coin at up to 25 cm distance and larger metal objects even up to 1 m. Modern metal detectors can also distinguish between different types of metal by analyzing the phase shift of the detected signal which might be some way to improve the design.

Video after the break.

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Hardware Hacker’s Marie Kondo: How Many LM386s Is Too Many?

May 2, 2020 by Elliot Williams 57 Comments

We’re running a contest on Making Tech at Home: building projects out of whatever you’ve got around the house. As a hacker who’s never had a lab outside of my apartment, house, or hackerspace, I had to laugh at the premise. Where the heck else would I hack?

The idea is that you’re constrained to whatever parts you’ve got on hand. But at the risk of sounding like Scrooge McDuck sitting on a mountain of toilet paper, I’ve got literally hundreds of potentiometers in my closet, a couple IMUs, more microcontrollers than you can shake a stick at, and 500 ml of etching solution waiting for me in the bathroom. Switches, motors, timing belts, nichrome wire…maybe I should put in an order for another kilogram of 3D printer filament. In short, unless it’s a specialty part or an eBay module, I’m basically set.

But apparently not everyone is so well endowed. I’ve heard rumors of people who purchase all of the parts for a particular project. That ain’t me. The guru of household minimalism asks us to weigh each object in our possession and ask “does it spark joy?”. And the answer, when I pull out the needed 3.3 V low-dropout regulator and get the project built now instead of three days from now, is “yes”.

And I’m not even a hoarder. (I keep telling myself.) The rule that keeps me on this side of sanity: I have a box for each type of part, and they are essentially fixed. When no more motors fit in the motor box, no more motors are ordered, no matter how sexy, until some project uses enough of them to free up space. It’s worked for the last 20 years, long before any of us had even heard of Marie Kondo.

So if you also sit atop a heap of VFD displays like Smaug under the Lonely Mountain, we want to see what you can do. If you do win, Digi-Key is sending you a $500 goodie box to replenish your stash. But even if you don’t win, you’ve freed up space in the “Robot Stuff” box. That’s like winning, and you deserve some new servos. Keep on hacking!

Mass Mask-Making Masterclass

May 2, 2020 by Kristina Panos 7 Comments

Just as 3D printers around the world have been churning out face shields, the thread injectors of home sewists have been stitching up fabric masks. Over the past several weeks, [Becky Stern] has made them for friends, family, neighbors, and anyone in her community who happens upon the box of free masks she’s left at a nearby bus stop. This is in addition the scores she has made and donated to health care workers so they can extend the life of their N95 masks.

If you’re going to make more than a few of anything, it just makes sense to make multiples at the same time and adjust the process for batch production. [Becky Stern] has some great ideas for ramping up assembly even further that include cutting out multiple main mask pieces at the same time, and ironing the pleats of several masks round robin style so you don’t waste time while they cool.

Even if you don’t dabble in the fabric arts, her method of kitting out the process of mask making is an interesting look into small-scale production.

Our favorite idea concerns the side bindings and the straps, which are the last part of the build and take the longest to do. [Becky] makes several miles of straps ahead of time with a 3D printed bias tape folder and then sews them all into a continuous strip. She can add the short side bindings to a bunch of masks at once, feeding them in one after the other so they end up strung together like sausages. Then she can just snip them apart and keep going, having saved both time and thread. Watch [Becky] make a single mask after the break and see how easy it is.

If sewing is a no-go for you, there are plenty of ways to help the PPE effort by firing up that printer.

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The Lost Art Of Component Scavenging

May 2, 2020 by Jenny List 115 Comments

With the easy and cheap availability of parts by Internet mail order, it’s easy to forget that acquiring electronic components was once a more tedious process, and it was common to use salvaged parts because they were what you had. Scouring a panel from a dumpster-find TV for the right resistor may now be a thing of the past, but it’s not entirely dead. [Ryan Flowers] was lucky enough to score a box of old CB radios at a garage sale, and takes us through a teardown in search of parts he can use to make a QRP amateur radio rig. Delving into aged electronics is right up our street!

An IF amplifier was high-tech back in '75. — An IF amplifier was high-tech back in ’75.

A possibility for a 27 MHz CB rig is to convert it to the neighbouring 10 m amateur band, but since these were all AM rigs, a mode that sees very little amateur use, it was better to part them out. It’s an interesting study in the evolution of radio design, as an entirely analogue design of mostly discrete components is revealed.

Careful inspection of the photographs reveals a Fairchild uA703 5-transistor IF amplifier chip in a metal can, but that’s about as high-tech as it gets. Unexpectedly there is a huge bank of crystals rather than the frequency synthesiser that would have been standard only a few years later.

He comes away with the chassis, switches and pots, and the RF inductors and crystals from the PCB. Those miniature Toko inductors used to be a common sight, but are now something of a rarity. If you fancy a wallow in semiconductors from this era we’ve previously taken a look at the vintage Fairchild catalogue, in which the uA703 is on page 398.

Some Strings Attached: Electric Tenor Guitar Built From Scratch

May 1, 2020 by Sven Gregori 4 Comments

It’s no secret that we have a soft spot for musical instruments here at Hackaday, especially for the weird and unusual ones. An instrument that definitely fits the unusual category is the four-string tenor guitar, which — as legend has it — originated back in the 1920s by frankensteining a banjo neck and a guitar body together. Despite being around for almost a century, they’re still rarely found outside some niche genres, which makes them an excellent choice when pursuing a unique sound experience. As someone looking for exactly that, [Ham-made] decided to build an electric tenor guitar entirely from scratch, and documented every step of it at great length.

Built from two random chunks of wood, a dissected single coil pickup, and a leftover piece of elk antlers, the result is even more unique than the sound experience itself. While the rather unorthodox, faceted body shape leaves no doubt that this is a handmade instrument, the real eye-catcher has to be the neck and its oddly spaced frets. Counting the frets, the math doesn’t seem to add up either, as the twelfth fret usually creates the octave, and as such should be at half the scale length (i.e. half the string’s length from the bridge at the body’s end to the nut at the neck’s end). Turns out that [Ham-made] went for a diatonic scale instead of the usual chromatic one, essentially leaving out the notes you anyway wouldn’t play in a standard Pop or Rock setup. Using an all-fifths tuning akin to cellos and mandolins, this will work nicely over all four strings.

Aesthetics are certainly a subjective matter, and [Ham-Made] is fully aware that people might feel downright offended by his creation, but as he also wants to “embrace mistakes and promote experimentation”, he encourages everyone with similar aspiration to simply go for it — and he’s certainly no stranger to unconventional instruments and recording equipment. But before the never-tiring tonewood debate sparks up, check out this scrap metal guitar.

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Linux Command Line Productivity With Tmux

May 1, 2020 by Al Williams 23 Comments

It is no secret that most Linux power users use the shell for many tasks, as for people who know what they are doing, it can be quite efficient. In addition, there are some tasks that can only be carried out from the command line, although their number shrinks every year. However, these days we are spoiled because you can have one X session running lots of terminals at once. If you log into a server, it might not have X. Or you might log into a computer over a slow connection where X is painful to use. What then? The modern answer is the tmux terminal multiplexer, and [zserge] has a thoughtful introduction to how you can use tmux for improved productivity at the command line.

In particular, he shares some configuration and offers sound advice. For example, do you really need a status bar that shows you CPU load at all times? Cool, yes, but not always a practical win.

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New Part Day: Raspberry Pi Camera Gets Serious With 12 Megapixels & Proper Lenses

May 1, 2020 by Jenny List 39 Comments

The Raspberry Pi Foundation have slipped out a new product, a $50 camera module with a larger sensor that increases the resolution from the 8 megapixels of its predecessor to a Sony IMX477R stacked, back-illuminated 12.3 megapixel sensor, and most interestingly adds a mounting ring for a C mount lens (the kind used with CCTV equipment) in place of the tiny fixed focus lenses of past Pi cameras. In addition there is a standard threaded tripod mount on the module, and an adapter ring for CS mount lens types. The camera cannot be used without a lens, but there are a few options available when ordering, like 16mm telephoto or 6mm wide angle lenses, if you do not already have a suitable lens on hand.

It’s an exciting move for photography experimenters, because for the first time it offers an affordable way into building custom cameras with both a higher quality sensor and a comprehensive selection of interchangeable lenses. We can imagine that the astronomers and microscopists among us will be enthusiastic about this development, as will those building automated wildlife cameras. For us though the excitement comes in the prospect of building decent quality cameras with custom form factors that break away from the conventional, because aside from a period when consumer digital cameras were in their infancy they have stuck rigidly to the same form factor dictated by a 35mm film canister. It’s clear that this module will be made into many different projects, and we are looking forward to featuring them.

At the time of writing the camera is sold out from all the usual suppliers, which follows the trend for Raspberry Pi products on their launch day. We didn’t manage to snag one, but perhaps with such an expensive module it’s best to step back for a moment and consider the project it will become part of rather than risking it joining the unfinished pile. While waiting for stock then perhaps the next best thing is to 3D print a C mount adapter for your existing Pi camera, or maybe even hook it up to a full-sized SLR lens.