Depending on what you build, you may or may not run into a lot of inductors. If you need small value coils, it is easy to make good-looking coils, and [JohnAudioTech] shows you how. Of course, doing the winding itself isn’t that hard, but you do need to know how to estimate the number of turns you need and how to validate the coil by measurement.
[John] uses a variety of techniques to estimate and measure his coils ranging from math to using an oscilloscope. He even uses an old-fashioned nomogram from a Radio Shack databook circa 1972.
Like many hackers, [Matthias Wandel] has a penchant for measuring the world around him, and quantifying the goings-on in his home is a bit of a hobby. And so when it came time to sense the current flowing in the wires of his house, he did what any of us would do: he built his own current sensing system.
What’s that you say? Any sane hacker would buy something like a Kill-a-Watt meter, or even perhaps use commercially available current transformers? Perhaps, but then one wouldn’t exactly be hacking, would one? [Matthias] opted to roll his own sensors for quite practical reasons: commercial meters don’t quite have the response time to catch the start-up spikes he was interested in seeing, and clamp-on current transformers require splitting the jacket on the nonmetallic cabling used in most residential wiring — doing so tends to run afoul of building codes. So his sensors were simply coils of wire shaped to fit the outside of the NM cable, with a bit of filtering to provide a cleaner signal in the high-noise environment of a lot of switch-mode power supplies.
Fed through an ADC board into a Raspberry Pi, [Matthias]’ sensor system did a surprisingly good job of catching the start-up surge of some tools around the shop. That led to the entertaining “Circuit Breaker Challenge” part of the video below, wherein we learn just what it really takes to pop the breaker on a 15-Amp branch circuit. Spoiler alert: it’s a lot.
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.
Look ma, no MCU!
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.
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.
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.
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.
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”→
