Designing An FM Drum Synth From Scratch

April 17, 2025 by 13 Comments

How it started: a simple repair job on a Roland drum machine. How it ended: a scratch-built FM drum synth module that’s completely analog, and completely cool.

[Moritz Klein]’s journey down the analog drum machine rabbit hole started with a Roland TR-909, a hybrid drum machine from the mid-80s that combined sampled sounds with analog synthesis. The unit [Moritz] picked up was having trouble with the decay on the kick drum, so he spread out the gloriously detailed schematic and got to work. He breadboarded a few sections of the kick drum circuit to aid troubleshooting, but one thing led to another and he was soon in new territory.

The video below is on the longish side, with the first third or so dedicated to recreating the circuits used to create the 909’s iconic sound, slightly modifying some of them to simplify construction. Like the schematic that started the whole thing, this section of the video is jam-packed with goodness, too much to detail here. But a few of the gems that caught our eye were the voltage-controlled amplifier (VCA) circuit that seems to make appearances in multiple places in the circuit, and the dead-simple wave-shaper circuit, which takes some of the harmonics out of the triangle wave oscillator’s output with just a couple of diodes and some resistors.

Once the 909’s kick and toms section had been breadboarded, [Moritz] turned his attention to adding something Roland hadn’t included: frequency modulation. He did this by adding a second, lower-frequency voltage-controlled oscillator (VCO) and using that to modulate the drum section. That resulted in a weird, metallic sound that can be tuned to imitate anything from a steel drum to a bell. He also added a hi-hat and cymbal section by mixing the square wave outputs on the VCOs through a funky XOR gate made from discrete components and a high-pass filter.

There’s a lot of information packed into this video, and by breaking everything down into small, simple blocks, [Moritz] makes it easy to understand analog synths and the circuits behind them.

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Bicycle Gearbox Does It By Folding

April 17, 2025 by 52 Comments

If you’ve spent any time on two wheels, you’ve certainly experienced the woes of poor bicycle shifting. You hit the button or twist the knob expecting a smooth transition into the next gear, only to be met with angry metallic clanking that you try to push though but ultimately can’t. Bicycle manufacturers collectively spent millions attempting to remedy this issue with the likes of gearboxes, electronic shifting, and even belt-driven bikes. But Praxis believes to have a better solution in their prototype HiT system.

Rather then moving a chain between gears, their novel solution works by folding gears into or away from a chain. These gears are made up of four separate segments that individually pivot around an axle near the cog’s center. These segments are carefully timed to ensure there is no interference with the chain making shifting look like a complex mechanical ballet.

While the shift initialization is handled electronically, the gear folding synchronization is mechanical. The combination of electronic and mechanical systems brings near-instant shifting under load at rotational rates of 100 RPM. Make sure to scroll through the product page and watch the videos showcasing the mechanism!

The HiT gearbox is a strange hybrid between a derailleur and a gearbox. It doesn’t contain a clutch based gear change system or even a CVT as seen in the famous Honda bike of old. It’s fully sealed with more robust chains and no moving chainline as in a derailleur system. The prototype is configurable between four or sixteen speeds, with the four speed consisting of two folding gear pairs connected with a chain and the sixteen speed featuring a separate pair of folding gears. The output is either concentric to the input, or above the input for certain types of mountain bikes.

Despite the high level of polish, this remains a prototype and we eagerly await what Praxis does next with the system. In the meantime, make sure to check out this chainless e-drive bicycle.

Supercon 2024: Exploring The Ocean With Open Source Hardware

April 17, 2025 by 10 Comments

If you had to guess, what do you think it would take to build an ocean-going buoy that could not only survive on its own without human intervention for more than two years, but return useful data the whole time? You’d probably assume such a feat would require beefy hardware, riding inside an expensive and relatively large watertight vessel of some type — and for good reason, the ocean is an unforgiving environment, and has sent far more robust hardware to the briny depths.

But as Wayne Pavalko found back in 2016, a little planning can go a long way. That’s when he launched the first of what he now calls Maker Buoys: a series of solar-powered drifting buoys that combine a collection of off-the-shelf sensor boards with an Arduino microcontroller and an Iridium Short-Burst Data (SBD) modem in a relatively simple watertight box.

He guessed that first buoy might last a few weeks to a month, but when he finally lost contact with it after 771 days, he realized there was real potential for reducing the cost and complexity of ocean research.

Wayne recalled the origin of his project and updated the audience on where it’s gone from there during his 2024 Supercon talk, Adventures in Ocean Tech: The Maker Buoy Journey. Even if you’re not interested in charting ocean currents with homebrew hardware, his story is an inspirational reminder that sometimes a fresh approach can help solve problems that might at first glance seem insurmountable.

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Budget Schlieren Imaging Setup Uses 3D Printing To Reveal The Unseen

April 17, 2025 by 9 Comments

We’re suckers here for projects that let you see the unseeable, and [Ayden Wardell Aerospace] provides that on a budget with their $30 Schlieren Imaging Setup. The unseeable in question is differences in air density– or, more precisely, differences in the refractive index of the fluid the imaging set up makes use of, in this case air. Think of how you can see waves of “heat” on a warm day– that’s lower-density hot air refracting light as it rises. Schlieren photography takes advantage of this, allowing to analyze fluid flows– for example, the mach cones in a DIY rocket nozzle, which is what got [Ayden Wardell Aerospace] interested in the technique.

Shock diamonds from a homemade rocket nozzle imaged by this setup.
Examining exhaust makes this a useful tool for [Aerospace].
This is a ‘classic’ mirror-and-lamp Schlieren set up.  You put the system you wish to film near the focal plane of a spherical mirror, and camera and light source out at twice the focal distance. Rays deflected by changes in refractive index miss the camera– usually one places a razor blade precisely to block them, but [Ayden] found that when using a smart phone that was unnecessary, which shocked this author.

While it is possible that [Ayden Wardell Aerospace] has technically constructed a shadowgraph, they claim that carefully positioning the smartphone allows the sharp edge of the case to replace the razor blade. A shadowgraph, which shows the second derivative of density, is a perfectly valid technique for flow visualization, and is superior to Schlieren photography in some circumstances– when looking at shock waves, for example.

Regardless, the great thing about this project is that [Ayden Wardell Aerospace] provides us with STLs for the mirror and smartphone mounting, as well as providing a BOM and a clear instructional video. Rather than arguing in the comments if this is “truly” Schlieren imaging, grab a mirror, extrude some filament, and test it for yourself!

There are many ways to do Schlieren images. We’ve highighted background-oriented techniques, and seen how to do it with a moiré pattern, or even a selfie stick. Still, this is the first time 3D printing has gotten involved and the build video below is quick and worth watching for those sweet, sweet Schlieren images. Continue reading “Budget Schlieren Imaging Setup Uses 3D Printing To Reveal The Unseen” →

Enigma buttons

Modernizing An Enigma Machine

April 17, 2025 by 6 Comments

This project by [Miro] is awesome, not only did he build a replica Enigma machine using modern technologies, but after completing it, he went back and revised several components to make it more usable. We’ve featured Enigma machines here before; they are complex combinations of mechanical and electrical components that form one of the most recognizable encryption methods in history.

His first Enigma machine was designed closely after the original. He used custom PCBs for the plugboard and lightboard, which significantly cleaned up the internal wiring. For the lightboard, he cleverly used a laser printer on semi-transparent paper to create crisp letters, illuminated from behind. For the keyboard, he again designed a custom PCB to connect all the switches. However, he encountered an unexpected setback due to error stack-up. We love that he took the time to document this issue and explain that the project didn’t come together perfectly on the first try and how some adjustments were needed along the way.
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A broken bolt is removed by welding on a hut and then using a wrench to unscrew.

Using A MIG Welder, Acetylene Torch, And Air Hammer To Remove A Broken Bolt

April 16, 2025 by 13 Comments

If your shop comes complete with a MIG welder, an acetylene torch, and an air hammer, then you have more options than most when it comes to removing broken bolts.

In this short video [Jim’s Automotive Machine Shop, Inc] takes us through the process of removing a broken manifold bolt: use a MIG welder to attach a washer, then attach a suitably sized nut and weld that onto the washer, heat the assembly with the acetylene torch, loosen up any corrosion on the threads by tapping with a hammer, then simply unscrew with your wrench! Everything is easy when you know how!

Of course if your shop doesn’t come complete with a MIG welder and acetylene torch you will have to get by with the old Easy Out screw extractor like the rest of us. And if you are faced with a nasty bolt situation keep in mind that lubrication can help.

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An Absolute Zero Of A Project

April 16, 2025 by 12 Comments

How would you go about determining absolute zero? Intuitively, it seems like you’d need some complicated physics setup with lasers and maybe some liquid helium. But as it turns out, all you need is some simple lab glassware and a heat gun. And a laser, of course.

To be clear, the method that [Markus Bindhammer] describes in the video below is only an estimation of absolute zero via Charles’s Law, which describes how gases expand when heated. To gather the needed data, [Marb] used a 50-ml glass syringe mounted horizontally on a stand and fitted with a thermocouple. Across from the plunger of the syringe he placed a VL6180 laser time-of-flight sensor, to measure the displacement of the plunger as the air within it expands.

Data from the TOF sensor and the thermocouple were recorded by a microcontroller as the air inside the syringe was gently heated. Plotting the volume of the gas versus the temperature results shows a nicely linear relationship, and the linear regression can be used to calculate the temperature at which the volume of the gas would be zero. The result: -268.82°C, or only about four degrees off from the accepted value of -273.15°. Not too shabby.

[Marb] has been on a tear lately with science projects like these; check out his open-source blood glucose measurement method or his all-in-one electrochemistry lab.

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