Tuning Fork Keeps This Throwback Digital Clock Ticking

February 13, 2021 by Dan Maloney 37 Comments

Whatever kind of clock you’re interested in building, you’re going to need to build an oscillator of some sort. Whether it be a pendulum, a balance wheel, or the atomic transitions of cesium or rubidium, something needs to go back and forth in a predictable way to form the timebase of the clock. And while it might not make the best timepiece in the world, a tuning fork certainly fits the bill and makes for a pretty interesting clock build.

One of the nice things about this build is that [Kris Slyka] got their inspiration from a tuning fork clock that we covered a while back — we love it when someone takes a cool concept and makes it their own. While both clocks use a 440 Hz tuning fork — that’s an A above middle C for the musically inclined — [Kris] changed up the excitation method for their build. She used a pair of off-the-shelf inductors, placed near the ends of each arm and bridged by a strong neodymium magnet to both sense the 440-Hz vibrations and to provide the kick needed to keep the fork vibrating.

As for the aesthetic of the build, we think [Kris] really nailed it. Using through-hole components, old-school seven-segment displays, and a home-etched PCB, she was able to capture a retro look that really works. The RS-232 port and the bell jar enclosure complete the feel, although we’re not sure about the custom character set [Kris] designed — it’s cool and all, but makes it hard for anyone else to read without a little practice. Regardless, this is a fun build, and we’d imagine the continuous tone coming from the clock is pretty pleasing.

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A Pair Of Steppers Are Put To Work In This Automatic Instrument Pickup Winder

December 13, 2020 by Dan Maloney 7 Comments

For something that’s basically a coil of wire around some magnetic pole pieces, an electric guitar pickup is a complicated bit of tech. So much about the tone of the instrument is dictated by how the pickup is wound that controlling the winding process is something best accomplished with a machine. This automatic pickup winder isn’t exactly a high-end machine, but it’s enough for the job at hand, and has some interesting possibilities for refinements.

First off, as [The Mixed Signal] points out, his pickups aren’t intended for use on a guitar. As we’ve seen before, the musical projects he has tackled are somewhat offbeat, and this single-pole pickup is destined for another unusual instrument. That’s not to say a guitar pickup couldn’t be wound on this machine, of course, as could inductors, solenoids, or Tesla coils. The running gear is built around two NEMA-17 stepper motors, one for the coil spindle and one for the winding carriage. The carriage runs on a short Acme lead screw and linear bearings, moving back and forth to wind the coil more or less evenly. An Arduino topped with a CNC shield runs the show, allowing for walk-away coil winding.

We do notice that the coil wire seems to bunch up at the ends of the coil form. We wonder if that could be cured by speeding up the carriage motor as it nears the end of the spool to spread the wire spacing out a bit. The nice thing about builds like these is the ease with which changes can be made — at the end of the day, it’s just code.

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Digging In The Dirt Yields Homebrew Inductors

September 13, 2020 by Dan Maloney 16 Comments

Let’s say you’re stranded on a desert island and want to get the news from the outside world. You’ll have to build your own crystal radio, of course, but your parts bin is nowhere to be found and Digi-Key isn’t delivering. So you’ll need to MacGuyver some components. Capacitors are easy with a couple of pieces of tinfoil, and a rectifier can be made from a pencil and a razor blade. But what about an inductor? Sure, air-core inductors will work, but just because you’re marooned doesn’t mean you’ve abandoned your engineering principles. Luckily, you’ve read [AC7ZL]’s treatise of making inductors from dirt, and with sand in abundance, you’re able to harvest enough material to put together some passable ferrite-core inductors.

Obviously, making your own inductive elements isn’t practical even in fanciful and contrived situations, but that doesn’t make the doing of it any less cool. The story begins with a walk in the Arizona desert many years ago, where [AC7ZL], aka [H.P. Friedrichs], spied bands of dark sand shooting through the underlying lighter sediments. These bands turned out to be magnetite, one of many iron-bearing minerals found in the area. Using a powerful magnet from an old hard drive and a plastic food container, he was able to harvest magnetite sand in abundance and refine it with multiple washing steps.

After experimentally determining the material’s permeability — about 2.3 H/m — [AC7ZL] proceeded with some practical applications. He was able to make a bar antenna for an AM radio by packing the sand into a PVC pipe and rewinding the coils around it. More permanent cores were made by mixing the sand with polyester resin and casting it into bars. Toroids were machined from fat bars of the composite on a lathe, much to the detriment of the cutting tools used.

The full-length PDF account of [AC7ZL]’s experiments makes for fascinating reading — the inductive elements he was able to create all performed great in everything from a Joule Thief to a Hartley oscillator up to 27 MHz. We love these kinds of stories, which remind us of some of the work being done by [Simplifier] and others.

A Broken Inductor As A Bike Chain Sensor

April 19, 2020 by Jenny List 31 Comments

If you have ever broken the ferrite core of an inductor, you’ll probably sympathize with [Oliver Mattos]. He accidentally stood on a ferrite-cored component, breaking it and rendering it useless. But utility is in the eye of the beholder, and instead of throwing it away he’s repurposed it as a chain sensor for his electric bicycle.

The broken inductor was positioned on the rear frame of the machine such that the chain passed through the area where the broken half of its core would once have been. As each link passes through the magnetic field it causes the inductance to change, and from this the speed, direction, and tension of the chain can be read.

Adding a 180 nF capacitor in parallel with the inductor creates a tuned circuit, and measuring the inductance is as straightforward as firing a single pulse at it and measuring the time it takes to go negative. Chain speed can be read by sensing the change in inductance as each link passes, tension by sensing the change in inductance as the chain is closer or further away, and direction by whether the chain is slack or not. It’s an ingenious and simple solution to measuring a bicycle chain, and we like it.

A lot of bicycle measurement systems have passed our way over the years, but it’s fair to say they have been more concerned with displays than sensors.

Link Coupling Antenna Tuner Wordless Workshop

March 15, 2020 by Al Williams 13 Comments

Remember “Wordless Workshop” in Popular Science? [Roy Doty] illustrated a household problem and the solution for it cobbled up in the main character’s garage workshop. We wonder what [Roy] would have done with YouTube? Maybe something like the video from [VE2TAE] and [VE2AEV] showing their link coupling antenna tuning build. You can watch the video after the break, and if you aren’t a fan of Jazz, you can mute the volume.

Like [Doty’s] cartoons, the video presumes you are going to have your own idea about dimensions and component values to fit your needs. But the construction is beautiful in its own right. The tubing wound into giant coils is impressive and brings back memories of the old days. However, the construction of the variable capacitors really got us excited. Big air variable caps may be hard to find, but the video makes them look easy to make.

A couple of nice looking knobs and panel meters make for a great looking tuner. With that spacing, we imagine it would handle full legal power without any difficulty at all. If you want to learn more about this type of tuner, [VK1OD] had a great page about it which seems to be defunct now. But the Internet Archive comes to our rescue, as usual.

The design is quite old, so even a 1934 copy of “Radio” can explain it (look on page 6). If you want to see a more wordy example of making variable capacitors — although they are smaller, the same principles apply — [N4DFP] has a good write up for that.

Of course, these days, most people expect their antenna tuning to be automatic. With some Lego, though, you could refit your manual one, if you like.

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LC Oscillators, Animated

January 2, 2020 by Al Williams 23 Comments

We wish that all the beautiful animations that are available today to understand math and electronics had been around when we were in school. Nonetheless, they are there for today’s students and [Learn Engineering] has another gorgeous one covering LC oscillation. Check it out, below.

If you are thoroughly grounded — no pun intended — in LC circuits, you probably won’t learn anything new. However, the animations are worth watching, just to admire them, if nothing else.

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Flexible PCBs Make The Fins Of This Robotic Fish

September 14, 2018 by Dan Maloney 10 Comments

We love a little outside-the-box thinking around here, and anytime we see robots that don’t use wheels and motors to do the moving, we take notice. So when a project touting robotic fish using soft-actuator fins crossed the tip line, we had to take a look.

It turns out that this robofish comes from the fertile mind of [Carl Bugeja], whose PCB motors and flexible actuators have been covered here before. The basic concept of these fish fins is derived from the latter project, which uses coils printed onto both sides of a flexible Kapton substrate. Positioned near a magnet, the actuators bend when a current runs through them. The video below shows two prototype robofish, each with four fins. The first is a scrap of foam with a magnet embedded; the fins did flap but the whole thing just weighed too much. Version two was much lighter and almost worked, but the tether to the driver is just too stiff to allow it to really flex its fins.

It looks like it has promise though, and we’re excited to see where [Carl] take this. Perhaps schools of tiny robofish patrolling for pollution?

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