Get Down To Some African Tunes With This HomeBrew Synth

South African [Afrorack] claims to have built the first home-built modular synthesiser in Africa. Whilst we can’t be sure of this (and to be frank, it doesn’t actually matter) what we can be sure of is that the latest additions to this rig sound pretty rad. (video, embedded below) There really isn’t much doubt that the African nations are the kings of rhythm, and that living in the less well-to-do areas you need to have a certain resourcefulness to use the materials around you. It’s not like you can just pop down to the local electronics store for a missing part, even if you had the funds for it.

The modular synth looks pretty nice, rough and ready like a real homebrew, and the use of an oil can as a bass drum and rice in a plastic skiff as an instrument might look crude, but sound pretty good. All three additions to the rig are simple spring-loaded solenoid affairs, but since off the shelf stuff is an expensive luxury, hand wound coils were in order. With a bobbin formed with a metal rod and two suitably trimmed fanta bottle lids, a wire spool holder sitting on what looks like a cake stand, a drill powered coil winder was constructed. We did smirk a little when in an early shot, wire was guided by hand, which was rapidly followed by an adjustment to guiding with a rag. Darn friction burns! We’re watching this with interest to see what the next additions will be, but for now, just sit back and nerd out to some sick African techno tunes!

Want to see a mess-o-wires turn into something meaningful? Got some Game Boys lying around needing something to do? How about a chiptune synth?

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SuperCapacitors Vs Batteries Again

Supercapacitors are definitely not the same as batteries, we all know that. They tend to have a very low operating voltage, and due to their operating principle of storing charge on parallel plates, their discharge curve is quite unfriendly for modern microcontroller devices. Energy storage efficiency per unit volume is also low compared with modern lithium polymer (LiPo) batteries so all in all they don’t look all that useful for many of our projects. However, as [Andreas Spiess’] latest video demonstrates, they do have some redeeming features that might make them useful for certain embedded applications.

The low operating voltage initially looks like an issue for devices operating at a typical 3.3V, and it’s tempting to simply wire a few in series and roll with it. But as [Andreas] explains in his typically clear manner, it would be necessary to have a complex power stage, operating in buck mode with capacitor voltage above the required level, and in boost mode when it heads below. Too complex – it’s much easier to simply stick with a low voltage bank of paralleled supercaps, and just operate always in boost mode. Even doing this, you’re not realistically going to get more than a handful of hours operating voltage with an always active device.

So why bother at all with supercaps, surely using a LiPo is so much easier and better? In many cases the answer is definitely a yes. But LiPo cells must not be charged in freezing temperatures (apart from certain special low temp products), else the cell can rapidly be destroyed due to lithium metal deposition at the anode. Also you need to be careful charging them, especially when they’re heavily discharged, as they are easily damaged without the proper treatment. LiPo cells operate based on chemical principles – lithium ions literally have to move around inside the structure, and eventually the battery will wear out.

Supercapacitors have the advantage of very long life (but sometimes, they do leak) much more aggressive charging and discharging behaviours and will operate down to very low temperatures. This makes them very useful when a large amount of power is available sporadically (for super fast charge cycles) or in places where temperatures stay persistently very low, such as up a mountain were solar will work, albeit slowly, but LiPo batteries will definitely not be suitable.

Other battery chemistries are available, such as Lithium Iron Phosphate which can tolerate the cold. Also you can always just insulate the battery with an integrated heater and preheat the battery to a safe charging temperature as well. So, just like everything with electronics, it’s important to choose the correct parts for your application, and it all starts with the power source. Supercapacitors might just hit an appropriate price/performance point for that special application you had in mind.

Supercapacitors aren’t really suitable for many applications, like powering an eBike or running your laptop, but hey, they did it anyway.

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A Super Speedy Lightweight Lossless Compression Algorithm

[Dominic Szablewski] was tinkering around with compressing RGB images, when he stumbled upon idea of how to make a simple lossless compression algorithm, resulting in the Quite OK Image Format, which seems to offer comparable file sizes to the PNG format but is so simple it runs up to 50 times faster for compression and up to four times faster for decompression. Implementation can be achieved with a miniscule 300 lines of C. Need a bit more detail on the real-world performance? Well [Dominic] has that covered too, with a complete set of benchmarks for your perusal.

Image formats are one of those things these days that are designed by consortium, with so much complexity wedged in making it hard to implement with limited resources, so we find it very refreshing to see someone going back to basics and producing something super lightweight, and plenty good enough in practical terms.

Other uses for the algorithm could be for super simple video compression, for applications where resource is tight and some low-effort bandwidth reduction would be beneficial. Implementation in a small FPGA would also be quite straightforward, since the memory requirement is quite low also.

The project is very new and already there are some tweaks happening to the format, so the GitHub project code may change without warning to reflect any corrections [Dominic] feels necessary.

Thanks [David] for the tip!

Do You Really Need To Dry Filament?

There’s a lot of opinions and theories around the storing and drying of 3D printing materials. Some people are absolutely convinced you must bake filament if it been stored outside an airtight bag, even for a few days. Some others have ‘never had a problem.’ So it’s about time someone in the know has done some testing to try to pin down the answer to the question we’re all asking; How bad is wet filament really?

[Thomas Sanladerer] setup a simple experiment, using samples of three common types of filament, specifically PLA, PET-G and ASA. He stored the samples in three environments, on his desk, outside in the garden, and finally submerged in water for a full week. What followed was a whole lot of printing, but they all did print.

Different filaments will absorb water at different rates, depending upon their chemical composition and the environment, nylon being apparently particularly fond of a good soaking. It would seem that the most obvious print defect that occurs with increased water absorption is that of stringing, and other than being annoying and reducing surface quality somewhat, it’s not all that serious in the grand scheme of things. It was interesting to note that water absorption doesn’t seem to affect the strength of the final part.
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Indoor Blimp Sails Through The Air Using Ultrasonic Transducers

Quadcopter type drones can be flown indoors, but unless you have a lot of space, it usually just ends in a crash. The prospect of being hit in the face by the propellor blades, spinning at 10k RPM doesn’t bear thinking about, and then there’s the noise. So, as a solution for indoor photography, or operating in public spaces, they are not viable. Japanese mobile operator DOCOMO has a new take on an old idea; the blimp. But, surely even a helium filled vehicle needs blades to steer around the room, we hear you cry? Not so, if you use a pair of specialised ultrasonic transducer arrays to move the air instead! (Video, embedded below)

Three banks of thrusters provide a 180 degree steerable net force

Details are scarce, but DOCOMO have fitted a helium balloon with modules on either side that can produce a steerable thrust, allowing the vehicle to effect all the expected aerial manoeuvres with ease and grace. The module at the bottom contains the control electronics, an upwards facing RGB LED for some extra bling, and of course a video camera to capture those all-important video shots.

We’d love to find a source for those ultrasonic transducer devices, and can only guess at the physical arrangement that allows for air to pass in one direction only, to effect a net thrust. We can find a few research papers hinting at the ability to use ultrasound to propel through air, like this one (bah! IEEExplore Paywall!) but to our knowledge,  this technology is not quite in the hands of hackers just yet.

Blimps are by no means scarce on these fine pages, here is a Blimpduino, an Arduino controlled 3D printed blimp, an illuminated blimp art installation by Japanese artist [Kensho Miyoshi] and if using helium is just too darn safe for you (or if you want to help prevent this allegedly precious resource from being lost into space) you could just build a remote controlled blimp using hydrogen instead. Just don’t light a match.

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Fifty Shades Of Brown: 3D Printing With Sugar

[Norbert Heinz] has been busy for the 2021 Hackaday Prize entry, working on the design of a direct granule extruder for 3D printing with waste materials, or materials that are not provided in the form of a filament. Sugar is pretty common in most households, so since that’s already available in granular form, [Norbert] gave 3D printing with granulated sugar a try. (Video, embedded below.)

[Editor’s note: He earned fifth place for this one! Well, not the sugar in particular, but the overall great work on granular extruders.]

Success was somewhat variable, as the gloopy material is notoriously fickle to work with, but the setup did produce some structures that stayed in one piece, at least for a while. Initially [Norbert] tried it real slow, effectively printing with the liquified sweet stuff, by dragging a molten blob of it around on the end of the extruder nozzle. Whilst this did work, the resulting print resolution did leave something to be desired. The next thing tried was increased print speed. This produced clearer prints, as the sugar did not have time to caramelise, or form a noticeable blob, but as soon as the bed started to cool, it caused it to crack badly.

Going slow seemed to be the way forward, as more time to cool may have reduced the stresses in the structure due to the increased cooling time. But anyway, the way we see it, is it’s fun trying, and if it fails, you can just eat it, so long as you disregard all that food safety stuff anyway.

[Norbert] documents the granule extruder journey on the project Hackaday.io page, so it should be straightforward enough to duplicate this is you were so inclined.

We’ve covered a few sugary hacks before; Need a renewable bed adhesive? out of glue stick? try sugar as a bed adhesive! Printing in gloopy, sloppy materials is nothing new at all, we covered it nearly ten years ago.

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Inverted Pendulum Balanced On A Drone

[Nicholas Rehm] works during the day at the Applied Physics Laboratory at Johns Hopkins, Maryland, so has considerable experience with a variety of UAV applications. The question arose about how the perseverance mars rover landing worked, which prompted [Nicholas] to hang a rock under his drone, attached via a winch. This proved to be interesting. But what is more interesting for us, is what happens when you try to attach an inverted pendulum to the top of a drone in flight? (video embedded, below)

This is a classic control theory problem, where you need to measure the angle of the pendulum with respect to the base, and close the loop by calculating the necessary acceleration from the pendulum angle. Typically this is demonstrated in one dimension only, but it is only a little more complicated to balance a pendulum with two degrees of freedom.

[Nicholas] first tried to derive the pendulum angle by simply removing the centering springs from an analog joystick, and using it to attach the pendulum rod to the drone body. As is quite obvious, this has a big drawback. The pendulum angle from vertical is now the sum of the joystick angle and the drone angle, which with the associated measurement errors, proved to be an unusable setup. Not to be discouraged, [Nicholas] simply added another IMU board to the bottom of the pendulum, and kept the joystick mechanism as a pivot only. And, as you can see from the video after the break, this indeed worked.

The flight controller is [Nicholas’] own project, dRehmFlight (GitHub), which is an Arduino library intended for the Teensy 4.0, using the ubiquitous MPU6050 6-DOF IMU. [Nicholas] also made an intro video for the controller, which may prove instructive for those wishing to go down this road to build their own VTOL aircraft. The code for pendulum experiment is not available at the time of writing, perhaps it will hit the GitHub in the future?

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