# Clever Test Rig Clarifies Capacitor Rules-of-Thumb

If you’ve done any amount of electronic design work, you’ll be familiar with the need for decoupling capacitors. Sometimes a chip’s datasheet will tell you exactly what kind of caps to place where, but quite often you’ll have to rely on experience and rules of thumb. For example, you might have heard that you should put 100 µF across the power supply pins and 100 nF close to each chip. But how close is “close”? And can that bigger cap really sit anywhere? [James Wilson] has been doing research to get some firm answers to those questions, and wrote down his findings in a fascinating blog post.

[James] designed a set of circuit boards that enabled him to place different types of capacitors at various distances along a set of PCB traces. By measuring the impedance of such a power distribution network (PDN) across frequency, he could then calculate its performance under different circumstances.

The ideal tool for those measurements would have been a vector network analyzer (VNA), but because [James] didn’t have such an instrument, he made a slightly simpler setup using a spectrum analyzer with a tracking generator. This can only measure the impedance’s magnitude, without any phase information, but that should be good enough for basic PDN characterization.

The results of [James]’s tests are pretty interesting, if not too surprising. For example, those 100 nF capacitors really ought to be placed within 10 mm of your chip if it’s operating at 100 MHz, but you can get away with even 10 cm if no signals go much above 1 MHz. A bulk 100 µF cap can be placed at 10 cm without much penalty in either case. Combining several capacitors of increasing size to get a low impedance across frequency is a good idea in principle, but you need to design the network carefully to avoid resonances between the various components. This is where a not-too-low equivalent series resistance (ESR) is actually a good thing, because it helps to dampen those resonances.

Overall, [James]’s blog post is a good primer on the topic, and gives a bit of much-needed context to those rules of thumb. If you want to dive deeper into the details of PDN design or the inductance of PCB traces, our own [Bil Herd] has made some excellent videos on those topics.

# Huygens’ Telescopes Weren’t Very Good, Now We Think We Know Why

[Christiaan Huygens] was a pretty decent mathematician and scientist by the standards of the 17th century. However, the telescopes he built were considered to be relatively poor in quality for the period. Now, as reported by Science News, we may know why. The well-known Huygens may have needed corrective glasses all along.

Huygens is known for, among other things, his contribution to astronomy. He discovered Titan, the largest moon of Saturn, and also studied the planet’s rings. He achieved this despite telescopes that were described at the time as fuzzy or blurrier than they otherwise should have been.

Huygens built two-lens telescopes, and would keep a table of which lenses to combine for different magnification levels. However, his calculations don’t align well with today’s understanding of optics. As it turns out, Huygens may have been nearsighted, which would account for why his telescopes were blurry. To his vision, they may indeed have been sharp, due to the nature of his own eyes. Supporting this are contemporary accounts that suggest Huygens father was nearsighted, with the condition perhaps running in the family. According to calculations by astronomer Alexander Pietrow, Huygens may have had 20/70 vision, in which he could only read at 20 feet what a person with “normal” vision could read from 70 feet away.

It’s a theory that answers a mildly-interesting mystery from many hundreds of years ago. These days, our troubles with telescopes are altogether more complex. If only a simple pair of glasses could solve NASA’s problems!

# Foldable PCB Becomes Tiny Rover

Typically, when you’re putting electronics in a robot, you install the various controller PCBs into the robot’s chassis. But what if the PCB itself was the chassis? [Carl Bugeja’s] latest design explores just that idea.

Yes, [Carl] decided to build a tiny robotic rover out of a foldable PCB. This choice was made as using a flexible foldable PCB would allow for the creation of a 3D chassis without the need for bulky connectors joining several boards together. A key part of the design was allowing the structure to unfold easily for serviceability’s sake. To that end, the structure is held together by the bolts that also act as the axles for the rover’s wheels. Even more brilliantly, the wheels are turned by motors built into the very PCB itself. Control is via a PlayStation controller, connected wirelessly to command the robot.

The little bot is surprisingly capable, especially when juiced up with a twin-cell lithium battery. It’s tiny, with minimal ground clearance, so it’s not the best at driving on rough surfaces. Having all-wheel-drive helps, though.

[Carl] specifically credits Altium Designer for making the design possible, thanks to its advanced 3D visualization tools that support foldable PCBs. Video after the break.

# Upgraded Plasma Thruster Is Smaller, More Powerful

When [Jay Bowles] demoed his first-generation ion thruster on Plasma Channel, the resulting video picked up millions of views and got hobbyists and professionals alike talking. While ionic lifters are nothing new, this robust multi-stage thruster looked (and sounded) more like a miniature jet engine than anything that had come before it. Optimizations would need to be made if there was even a chance to put the high-voltage powerplant to use, but [Jay] was clearly onto something.

Fast forward six months, and he’s back with his Mark II thruster. It operates under the same core principles as the earlier build, but swaps out the open-frame design and acrylic construction for a rigid 3D printed structure designed to more effectively channel incoming air. The end result is a thruster that’s smaller and has a lower mass, while at the same time boasting nearly double the exhaust velocity of its predecessor. Continue reading “Upgraded Plasma Thruster Is Smaller, More Powerful”

# Cold War Military Telephones Now Usable Thanks To DIY Switch Build

The TA-1042 is the most badass looking telephone you’ll ever see. It’s a digital military telephone from the 1980s, but sadly non-functional unless it’s hooked up to the military phone switches it was designed to work with. These days, they’re really only useful as a heavy object to throw at somebody… that is, unless you had the suitable supporting hardware. As it turns out, [Nick] and [Rob] were able to whip up exactly that.

Their project involved implementing the TA-1042’s proprietary switching protocol on a Raspberry Pi Pico. The microcontroller’s unique Programmable I/O subsystem proved perfect for the task. With a little programming and a hat for the Pico to interface with the hardware, they were able to get the TA-1042 working as intended. It involved learning how to encode and decode the Manchester encoded data used by the Digital Non-secure Voice Terminal equipment. Notably, the TA-1042 isn’t the only phone you can use with this setup. You can also hook up other US military DNVT phones, like the TA-954 or TA-1035.

If you want this hardware for yourself, you can simply buy one of [Nick] and [Rob]’s DNVT switches from Tindie. Alternatively, you can roll your own with the source code provided on GitHub.

We’ve seen these phones before repurposed in an altogether different fashion. We’ve also taken a deep dive into the details of the military’s AUTOVON network.

# 2022 Supercon: Jac And Ralf Explore The Secrets Of The Digital Compact Cassette

During the 1990s, music was almost invariably stored on CDs or cassette tapes. When the new millennium came around, physical formats became obsolete as music moved first to MP3 files, and later to network streams. But a few years before that big transition, there were several attempts at replacing the aging cassette and CD formats with something more modern. You might remember the likes of MiniDisc and Super Audio CD, but there were a few other contenders around.

The Digital Compact Cassette, or DCC, was one such format. Released by Philips in 1992 as a replacement for the analog audio cassette, it failed to gain traction in the market and disappeared before most people had even heard of it. Not so for [Jac Goudsmit] and [Ralf Porankiewicz] however, who have spent years researching all aspects of the DCC system and shared some of the results in their 2022 Supercon talk.

[Ralf] is the curator of the DCC Museum in Cathedral City, California, which owns examples of all DCC equipment ever released, as well as several devices that never made it to market. He also aims to document the history of audio recording and DCC’s contribution to it, which goes further than you might think. For example, the audio compression format used in the DCC system, called PASC, was an early version of what would later become MP3 – though most histories of audio compression ignore this fact.

[Jac], for his part, made an extensive study of all the technical features of the DCC format. He has written numerous articles about his findings, first in the DCC FAQ and later by maintaining the relevant Wikipedia articles. He is running several projects aimed at keeping the format alive, often in collaboration with the DCC Museum.

[Jac] and [Ralf] begin their talk with a brief introduction to the system and its media. DCC players were designed to be compatible with analog audio cassettes, so DCC cartridges are the same basic size, though with a different type of tape inside. Playback devices contain a complex set of magnetic heads to read either the analog signals from classic tapes, or the digital data stored on DCCs.

One unique feature of DCC is Interactive Text Transfer Service, or ITTS, which is a separate data area on the tape that can hold additional information like song lyrics or even simple animations. It was intended to be displayed on players that supported it, but no such devices were ever released. Luckily, [Jac] and [Ralf] managed to find a rare ITTS decoder system used in a tape mastering facility, and were able to reveal the contents of this “secret track”, which is present on all prerecorded tapes, for the first time.

User-recorded tapes never had any ITTS data, and differed from prerecorded ones in several other ways, too. The most obvious difference was that professionally-made tapes could be indexed by song title, while home-made ones could only jump to track numbers. [Jac] and [Ralf] are however working to enable all the professional features on home-made tapes as well, through a number of software and hardware projects.

The most basic software needed is an encoder and decoder for the PASC format, which [Jac] developed from existing MP1 sofware. But to explore some of the more obscure hardware features, he had to reverse-engineer several different DCC players. This led him to discover many interesting half-finished features: the ITTS data sector is one example, but he also found out that some players send ready-to-use VU meter data to their front panel, even though they are unable to display that information.

[Jac] was also one of the first people to buy the DCC-175 portable DCC player when it was released in 1995. This was the only DCC player ever sold with a computer interface, allowing direct transfer of digital audio between a computer and a DCC tape. The parallel port interface and its accompanying Windows 9x software are completely obsolete and unusable with modern PCs, so [Jac] is working on directly accessing the data from the DCC-175 through a custom cable. He’s making good progress: he already figured out the electrical interface and wrote some software that enables him to control the tape recorder directly.

We can’t help but be impressed by the amount of effort both [Jac] and [Ralf] have put into understanding and documenting all the intricacies of a long-obsolete audio format. Thanks to their efforts, we can still appreciate the impressive technology behind DCC – even if it never came close to replacing its analog cousin.

# Electric Skateboard Becomes Mobile Skate Park

While building a skate park might not appear to have much in common with software development, at they very least, they both suffer from a familiar problem: scalability. Bigger skate parks need more ramps and features, and there’s no real way to scale up a construction project like this efficiently like you could with certain kinds of software other than simply building more features. This was something [Kirk] noticed, but was able to scale up a skate park in a way we’ve never thought of before. He built a mobile skateboard ramp that can turn any place into a skate park.

The mobile and approximately sidewalk-width platform is able to move around thanks to an electric skateboard as its foundation. It adds a NVIDIA Jetson Nano for control with a PS4 controller for input, although steering a skateboard with an actuator took a few prototypes to figure out since skateboards are designed to be steered by shifting the rider’s weight. Since they are already designed to carry a human-amount of weight, though, it was at least able to tote the ramp around with relative ease. Another problem was lowering the ramp into position when it got to the desired area, but with an electrically-controlled jack and a few rounds of debugging was eventually able to do this without much issue.

With all of that project development behind him, [Kirk] can finally realize his dream of having ramps scattered all across his neighborhood like in the classic videogame Paperboy, without needing to build them all individually or ask for permission to place them around his neighbor’s homes. For any future iterations of this build, we might consider adding tank tracks to the electric skateboard for better off-road performance, like facilitating a jump across a patch of grass.