A Brief Look Inside A Homebrew Digital Sampler From 1979

June 17, 2024 by Dan Maloney 12 Comments

While we generally prefer to bring our readers as much information about a project as possible, sometimes we just have to go with what we see. That generally happens with new projects and work in progress, but it can also happen with old projects. Sometimes very old indeed, as is the case with this digital sampling unit for analog oscilloscopes, circa 1979.

We’ve got precious little to go on with this one other than the bit of eye candy in the video tour below and its description. Luckily, we’ve had a few private conversations with its maker, [Mitsuru Yamada], over the years, enough to piece together a little of the back story here — with apologies for any wrong assumptions, of course.

Built when he was only 19, this sampler was an attempt to build something that couldn’t be bought, at least not for a reasonable price. With no inexpensive monolithic analog-to-digital converters on the market, he decided to roll his own. A few years back he recreated the core of that with his all-discrete successive approximation ADC.

The sampler shown below has an 8-bit SAR ADC using discrete CMOS logic and enough NMOS memory to store 256 samples. You can see the ADC and memory cards in the homebrew card cage made from aluminum angle stock. The front panel has a ton of controls and sports a wide-range attenuator, DC offset, and trigger circuit with both manual and automatic settings.

It’s an impressive build, especially for a 19-year-old with presumably limited resources. We’ve reached out to [Yamada-san] in the hope that he’ll be able to provide more details on what’s under the hood and if this still works after all these years. We’ll pass along whatever we get, but in the meantime, enjoy.

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3D Printing A Bottle Labeling Assembly Line

June 16, 2024 by Tom Nardi 11 Comments

We’re not completely sure why [Fraens] needs to label so many glass bottles at home. Perhaps he’s brewing his own beer, or making jams. Whatever the reason is, it was justification enough to build an absolutely incredible labeling machine that you could mistake for a piece of industrial gear…if it wasn’t for the fact that majority of the device is constructed out of orange 3D printed plastic.

As we’ve come to expect, [Fraens] has documented the build with a detailed write-up on his site — but in this case, you’ve really got to watch the video below to truly appreciate how intricate the operation of this machine is. Watching it reminded us of an episode of How It’s Made, with the added bonus that you not only get to see how the machine functions, but how it was built in the first place.

Nearly every part of the machine, outside the fasteners, smooth rods, a couple of acrylic panels, and a few sections of aluminum extrusion, were 3D printed. You might think this would result in a wobbly machine with sloppy tolerances, but [Fraens] is truly a master of knowing when and where you can get away with using printed parts. So for example, while the glue rollers could be done in printed plastic, they still needed metal rods run through the middle for strength and proper bearings to rotate on.

Looking at the totality of this build, it’s hard to imagine how it could have been accomplished via traditional methods. Sure you could have sourced the rollers and gears from a supplier to save some plastic (at an added expense, no doubt), but there’s so many unique components that simply needed to be fabricated. For example, all the guides that keep the label heading in the right direction through the mechanism, or the interchangeable collars which let you select the pattern of glue which is to be applied. Maybe if you had a whole machine shop at your disposal, but that’s a lot more expensive and complex a proposition than the pair of desktop 3D printers [Fraens] used to crank out this masterpiece.

If the name (and penchant for orange plastic) seems familiar, it’s because we’ve featured several builds from [Fraens] in the past. This one may be the most technically impressive so far, but that doesn’t diminish the brilliance of his vibratory rock tumbler or cigarette stuffing machine.

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Busted: Toilet Paper As Solder Wick

June 14, 2024 by Dan Maloney 29 Comments

It didn’t take long for us to get an answer to the question nobody was asking: Can you use toilet paper as solder wick? And unsurprisingly, the answer is a resounding “No.”

Confused? If so, you probably missed our article a few days ago describing the repair of corroded card edge connectors with a bit of homebrew HASL. Granted, the process wasn’t exactly hot air solder leveling, at least not the way PCB fabs do it to protect exposed copper traces. It was more of an en masse tinning process, for which [Adrian] used a fair amount of desoldering wick to pull excess solder off the pins.

During that restoration, [Adrian] mentioned hearing that common toilet paper could be used as a cheap substitute for desoldering wick. We were skeptical but passed along the tip hoping someone would comment on it. Enter [KDawg], who took up the challenge and gave it a whirl. The video below shows attempts to tin a few pins on a similar card-edge connector and remove the excess with toilet paper. The tests are done using 63:37 lead-tin solder, plus and minus flux, and using Great Value TP in more or less the same manner you’d use desoldering braid. The results are pretty much what you’d expect, with charred toilet paper and no appreciable solder removal. The closest it comes to working is when the TP sucks up the melted flux. Stay tuned for the bonus positive control footage at the end, though; watching that legit Chemtronics braid do its thing is oddly satisfying.

So, unless there’s some trick to it, [KDawg] seems to have busted this myth. If anyone else wants to give it a try, we’ll be happy to cover it.

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This Open Source Active Probe Won’t Break The Bank

June 13, 2024 by Dan Maloney 20 Comments

If you’re like us, the oscilloscope on your bench is nothing special. The lower end of the market is filled with cheap but capable scopes that get the job done, as long as the job doesn’t get too far up the spectrum. That’s where fancier scopes with active probes might be required, and such things are budget-busters for mere mortals.

Then again, something like this open source 2 GHz active probe might be able to change the dynamics a bit. It comes to us from [James Wilson], who began tinkering with the design back in 2022. That’s when he learned about the chip at the center of this build: the BUF802. It’s a wide-bandwidth, high-input-impedance JFET buffer that seemed perfect for the job, and designed a high-impedance, low-capacitance probe covering DC to 2 GHz probe with 10:1 attenuation around it.

[James]’ blog post on the design and build reads like a lesson in high-frequency design. The specifics are a little above our pay grade, but the overall design uses both the BUF802 and an OPA140 precision op-amp. The low-offset op-amp buffers DC and lower frequencies, leaving higher frequencies to the BUF802. A lot of care was put into the four-layer PCB design, as well as ample use of simulation to make sure everything would work. Particularly interesting was the use of openEMS to tweak the width of the output trace to hit the desired 50 ohm impedance.

OpenSCAD Cranks Out Parametric CNC Clamps

June 11, 2024 by Tom Nardi 7 Comments

If you’ve ever used a CNC router or mill, you’ll know how many little things need to go right before you get anything resembling acceptable results. We could (and probably should?) run a whole series of posts on selecting the correct bit for the job at hand and figuring out the appropriate feeds and speeds. But before you even get to that point, there’s something even more critical you need to do: hold the workpiece down so it doesn’t blast off into orbit when the tool touches it.

Now that might sound like an easy enough job, and for basic flat stock, it often is. But if you’ve got an oddly shaped piece of material, you’ll quickly realize how inadequate those trusty c-clamps really are. When you get to that point, it might time to check out these OpenSCAD hold down clamps from [ostat]. Thanks to its parametric nature, you can plug whatever dimensions you need into the script, and in a few seconds it will spit out an STL file for a bespoke clamp that you can print out and put to work.

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The Cheap CNC3018 Gets A Proper Revamp

June 8, 2024 by Dave Rowntree 25 Comments

Many people have been attracted to the low price and big dreams of the CNC3018 desktop CNC router. If you’re quick, you can pick one up on the usual second-hand sales sites with little wear and tear for a steal. They’re not perfect machines by any stretch of the imagination, but they can be improved upon, and undoubtedly useful so long as you keep your expectations realistic.

[ForOurGood] has set about such an improvement process and documented their journey in a whopping eight-part (so far!) video series. The video linked below is the most recent in the series and is dedicated to creating a brushless spindle motor on a budget.

As you would expect from such a machine, you get exactly what you pay for. The low cost translates to thinner than ideal metal plates, aluminium where steel would be better, lower-duty linear rails, and wimpy lead screws. The spindle also suffers from cost-cutting, as does the size of the stepper motors. But for the price, all is forgiven. The fact that they can even turn a profit on these machines shows the manufacturing prowess of the Chinese factories.

We covered the CNC 3018 a while back, and the comments of that post are a true gold mine for those wanting to try desktop CNC. Warning, though: It’s a fair bit harder to master than 3D printing!

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Gamma Ray Spectroscopy The Pomelo Way

June 5, 2024 by Dan Maloney 15 Comments

Depending on the circumstances you find yourself in, a Geiger counter can be a tremendously useful tool. With just a click or a chirp, it can tell you if any invisible threats lurk. But a Geiger counter is a “yes or no” instrument; it can only tell you if an ionizing event occurred, revealing nothing about the energy of the radiation. For that, you need something like this gamma-ray spectroscope.

Dubbed the Pomelo by [mihai.cuciuc], the detector is a homebrew solid-state scintillation counter made from a thallium-doped cesium iodide crystal and a silicon photomultiplier. The scintillator is potted in silicone in a 3D printed enclosure, to protect the hygroscopic crystal from both humidity and light. There’s also a temperature sensor on the detector board for thermal compensation. The Pomelo Core board interfaces with the physics package and takes care of pulse shaping and peak detection, while a separate Pomelo Zest board has an ESP32-C6, a small LCD and buttons for UI, SD card and USB interfaces, and an 18650 power supply. Plus a piezo speaker, because a spectroscope needs clicks, too.

The ability to determine the energy of incident photons is the real kicker here, though. Pomelo can detect energies from 50 keV all the way up to 3 MeV, and display them as graphs using linear or log scales. The short video below shows the Pomelo in use on samples of radioactive americium and thorium, showing different spectra for each.

[mihai.cuciuc] took inspiration for the Pomelo from this DIY spectrometer as well as the CosmicPi.

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