Impromptu Metal Detector Built From The Junk Bin

August 30, 2021 by Tom Nardi 12 Comments

Have you ever found yourself suddenly in need of finding a small metal object hidden in the woods? No? Well, neither have we. But we can’t say the same thing for [zaphod], who’s family was hoping to settle a dispute by finding the surveyor stakes that marked the corners of their property. It was a perfect job for a metal detector, but since they didn’t own one, a serviceable unit had to be assembled from literal garbage.

To start with, [zaphod] had to research how a metal detector actually works. After reviewing the pros and cons of various approaches, the decision was made to go with a beat frequency oscillator (BFO) circuit. It’s not the greatest design, it might even be the worst, but it could be built with the parts on hand and sometimes that’s all that matters. After packing a 2N3904 transistor, an LM386 amplifier, and every Hackaday reader’s favorite chip the 555 timer into an enclosure along with some of their closest friends, it was time to build the rest of the metal detector.

The sensor coil was made by salvaging the wire from an old fluorescent lamp ballast and winding it around the lid of a bucket 27 times. This was mounted to the end of a broom handle with some angle pieces made from PVC sheet material, being careful not to use any metal fasteners that would throw off the detector. With the handle of an old drill in the middle to hold onto, the metal detector was complete and actually looked the part.

So did [zaphod] save the day by finding the surveyor stakes and reconnoitering the family’s plot? Unfortunately, no. It wasn’t a technical failure though; the metal detector did appear to work, although it took a pretty sizable object to set it off. The real problem was that, after looking more closely into it, the surveyors only put down one stake unless they are specifically instructed otherwise. Since they already knew where that one was…

If your homemade metal detector can’t find something that was never there, did it really fail? Just a little something to meditate on. In any event, when even the cheapest smart bulb is packing a microcontroller powerful enough to emulate early home computers, we’re always happy to see somebody keep the old ways alive with a handful of ICs.

Automatic Coil Winder Gets It Done With Simple Hardware And Software

July 25, 2021 by Dan Maloney 11 Comments

We’ve grown to expect seeing mechatronics project incorporate a standard complement of components, things like stepper motors, Arduinos, lead screws, timing belts and pulleys, and aluminum extrusions. So when a project comes along that breaks that mold, even just a little, we sit up and take notice.

Departing somewhat from this hardware hacking lingua franca is [tuenhidiy]’s automatic coil winder, which instead of aluminum extrusions and 3D-printed connectors uses simple PVC pipe and fittings as a frame. Cheap, readily available, and easily worked, the PVC does a fine job here, and likely would on any project where forces are low and precision isn’t critical. The PVC frame holds two drive motors, one to wind the wire onto a form and one to drive a lead screw that moves the form back and forth. An Arduino with a CNC shield takes care of driving the motors, and the G-code needed to do so is generated by a simple spreadsheet that takes into account the number turns desired, the number of layers, the dimensions of the spool, and the diameters of the wire. The video below shows the machine going through its paces, with pretty neat and tidy results.

Being such a tedious task, this is far from the first coil winder we’ve seen. Some adhere to the standard design language, some take off in another direction entirely, but they’re all instructive and fun to watch in action.

Continue reading “Automatic Coil Winder Gets It Done With Simple Hardware And Software” →

Macro Model Makes Atomic Force Microscopy Easier To Understand

June 12, 2021 by Dan Maloney 6 Comments

For anyone that’s fiddled around with a magnifying glass, it’s pretty easy to understand how optical microscopes work. And as microscopes are just an elaboration on a simple hand lens, so too are electron microscopes an elaboration on the optical kind, with electrons and magnets standing in for light and lenses. But atomic force microscopes? Now those take a little effort to wrap your brain around.

Luckily for us, [Zachary Tong] over at the Breaking Taps YouTube channel recently got his hands on a remarkably compact atomic force microscope, which led to this video about how AFM works. Before diving into the commercial unit — but not before sharing some eye-candy shots of what it can do — [Zach] helpfully goes through AFM basics with what amounts to a macro version of the instrument.

His macro-AFM uses an old 3D-printer as an X-Y-Z gantry, with a probe head added to the printer’s extruder. The probe is simply a sharp stylus on the end of a springy armature, which is excited into up-and-down oscillation by a voice coil and a magnet. The probe rasters over a sample — he looked at his 3D-printed lattices — while bouncing up and down over the surface features. A current induced in the voice coil by the armature produces a signal that’s proportional to how far the probe traveled to reach the surface, allowing him to map the sample’s features.

The actual AFM does basically the same thing, albeit at a much finer scale. The probe is a MEMS device attached to — and dwarfed by — a piece of PCB. [Zach] used the device to image a range of samples, all of which revealed fascinating details about the nanoscale realm. The scans are beautiful, to be sure, but we really appreciated the clear and accessible explanation of AFM.

Continue reading “Macro Model Makes Atomic Force Microscopy Easier To Understand” →

Flat Transformer Gives This PCB Tesla Coil Some Kick

June 9, 2021 by Dan Maloney 16 Comments

Arguably, the most tedious part of any Tesla coil build is winding the transformer. Getting that fine wire wound onto a suitable form, making everything neat, and making sure it’s electrically and mechanically sound can be tricky, and it’s a make-or-break proposition, both in terms of the function and the aesthetics of the final product. So this high-output printed circuit Tesla should take away some of that tedium and uncertainty.

Now, PCB coils are nothing new — we’ve seen plenty of examples used for everything from motors to speakers. We’ve even seen a few PCB Tesla coils, but as [Ray Ring] points out, these have mostly been lower-output coils that fail to bring the heat, as it were. His printed coil generates some pretty serious streamers — a foot long (30 cm) in some cases. The secondary of the coil has 6-mil traces spaced 6 mils apart, for a total of 240 turns. The primary is a single 240-mil trace on the other side of the board, and the whole thing is potted in a clear, two-part epoxy resin to prevent arcing. Driven by the non-resonant half-bridge driver living on the PCB below it, the coil can really pack a punch. A complete schematic and build info can be found in the link above, while the video below shows off just what it can do.

Honestly, for the amount of work the PCB coil saves, we’re tempted to give this a try. It might not have the classic good looks of a hand-wound coil, but it certainly gets the job done. Continue reading “Flat Transformer Gives This PCB Tesla Coil Some Kick” →

Tonewheels Warble In This Organ-Inspired Musical Instrument

February 10, 2021 by Dan Maloney 9 Comments

Younger readers may not recall the days when every mall had a music store — not the kind where tapes and LPs were sold, but the kind where you could buy instruments. These places inevitably had an employee belting out mall-music to all and sundry on an electric organ. And more often than not, the organist was playing a Hammond organ, with the distinct sound of these instruments generated by something similar to this tonewheel organ robot.

Tonewheels are toothed ferromagnetic wheels that are rotated near a pickup coil. This induces a current that can be amplified; alter the tooth profile or change the speed of rotation, and you’ve got control over the sounds produced. While a Hammond organ uses this technique to produce a wide range of sounds, [The Mixed Signal]’s effort is considerably more modest but nonetheless interesting. A stepper motor and a 1:8 ratio 3D-printed gearbox power a pair of shafts which each carry three different tonewheels. The tonewheels themselves are laser-cut from mild steel and range from what look like spur gears to wheels with but a few large lobes. This is a step up from the previous version of this instrument, which used tonewheels 3D-printed from magnetic filament.

Each tonewheel has its own pickup, wound using a coil winder that [TheMixed Signal] previously built. Each coil has a soft iron core, allowing for the addition of one or more neodymium bias magnets, which dramatically alters the tone. The video below shows the build and a demo; skip ahead to 16:10 or so if you just want to hear the instrument play. It’s — interesting. But it’s clearly a work in progress, and we’re eager to see where it goes. Continue reading “Tonewheels Warble In This Organ-Inspired Musical Instrument” →

Handheld Slayer Exciter Wand Makes For Easy High Voltage Magic

January 13, 2021 by Tom Nardi 35 Comments

It’s often said that any sufficiently advanced technology is indistinguishable from magic, and when a DIY device lets you light up fluorescent bulbs with a flick of the wrist, it’s certainly not hard to see why. The latest creation from [Jay Bowles], this high voltage wand is actually a Slayer Exciter coil that’s able to boost the output of a standard 9 V alkaline or rechargeable battery high enough to perform some of the wireless power tricks we usually associate with the more complex Tesla coil.

We really can’t overstate how simple it is to build one of these yourself. Sure you’ll still need to wind the coil, but if you can chuck the 1/2 inch acrylic tube into a electric drill you should be able to make short work of it. Once you’ve wound your secondary coil from 32 gauge magnet wire, you only need a couple turns of common doorbell wire to make up the primary.

Think there must be some complex electronics hiding in the handle? Far from it. All that’s hidden by that faux-leather wrapping is a transistor to do the high-speed switching, an LED functioning as both the power indicator and the circuit’s diode, and a resistor. [Jay] put it all together dead bug style, but you could do it on a scrap of perfboard if you’d like something a little more robust.

Being a big believer in STEM education, [Jay] says the wand was designed to be as kid-friendly as possible so he could gift it to his young niece and nephew. Inspiring the next generation is certainly something we respect around these parts, though we think there’s plenty of adults who wouldn’t have been disappointed if they unwrapped a gadget like this over the holidays.

If you’d like to play around with a Slayer but aren’t into the whole Harry Potter motif, you might be interested in the larger and more capable version [Jay] built earlier in the year.

Continue reading “Handheld Slayer Exciter Wand Makes For Easy High Voltage Magic” →

Custom Coil Lets Mouse Charge Without Wires

January 13, 2021 by Tom Nardi 22 Comments

It’s 2021, shouldn’t all of our devices be able to pull the power they need from the ether? [Sasa Karanovic] certainly thinks so, which is why he recently took it upon himself to add wireless charging capabilities to his desktop computer peripherals. The Qi transmitter and receiver modules are relatively cheap and easy to come by, the trick is in getting them installed.

The keyboard gets non-invasive Qi charging.

For the keyboard, [Sasa] took the path of least resistance. The receiver coil lives inside a little 3D printed box attached to the back, and power is routed through a hacked up right-angle USB cable. It’s a simple addition that doesn’t make any permanent changes to the keyboard; perfect for those who don’t want to risk toasting their gear.

But that wasn’t really an option for the mouse. Obviously the Qi hardware would have to go on the inside, but at a glance it was clear there wasn’t enough room to mount the stock coil. So [Sasa] pulled the original coil apart and rewound it around a small 3D printed jig. This resulting coil was perfectly sized to fit inside the flat area on the left side of the mouse with no apparent degradation in charging ability. Wiring the module up to an unpopulated pad on the PCB allowed him to easily inject the 5 V output into the device’s existing charging circuitry.

We’ve seen plenty of aftermarket Qi charging coils take up permanent residence in various gadgets, but rewinding the coil is a neat trick that we’ve only seen pulled off a couple times in the past. Something to file away mentally should you ever want to wirelessly power up one of your projects.

Continue reading “Custom Coil Lets Mouse Charge Without Wires” →