Pressure Gauge Built In A Vacuum

February 23, 2022 by 6 Comments

Necessity might be the mother of all invention, but we often find that inventions around here are just as often driven by expensive off-the-shelf parts and a lack of willingness to spend top dollar for them. More often than not, we find people building their own tools or parts as if these high prices are a challenge instead of simply shrugging and ordering them from a supplier. The latest in those accepting the challenge of building their own parts is [Advanced Tinkering] who needed a specialty pressure gauge for a vacuum chamber.

In this specific case, the sensor itself is not too highly priced but the controller for it was the deal-breaker, so with a trusty Arduino in hand a custom gauge was fashioned once the sensor was acquired. This one uses an external analog-to-digital converter to interface with the sensor with 16-bit resolution, along with some circuitry to bring the ~8 V output of the sensor down to the 5 V required by the microcontroller. [Advanced Tinkering] wanted a custom live readout as well, so a 3D printed enclosure was built that includes both an LCD readout of the pressure and a screen with a graph of the pressure over time.

For anyone else making sensitive pressure measurements in a vacuum chamber, [Advanced Tinkering] made the project code available on a GitHub page. It’s a great solution to an otherwise overpriced part provided you have the time to build something custom. If you’re looking for something a little less delicate, though, take a look at this no-battery pressure sensor meant to ride along on a bicycle wheel.

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Astra’s Frugal Design Leads To Latest Unusual Failure

February 23, 2022 by 36 Comments

We’ve all heard it said, and it bears repeating: getting to space is hard. But it actually gets even harder the smaller your booster is. That’s because the structure, engines, avionics, and useful payload of a rocket only make up a tiny portion of its liftoff mass, while the rest is dedicated to the propellant it must expend to reach orbital velocity. That’s why a Falcon 9 tipping the scales at 549,054 kilograms (1,207,920 pounds) can only loft a payload of 22,800 kg (50,265 lb) — roughly 4% of its takeoff weight.

As you might imagine, there’s a lower limit where there simply isn’t enough mass in the equation for the hardware necessary to build a fully functional rocket. But where is that limit? That’s precisely what aerospace newcomer Astra is trying to find out. Their Rocket 3 is among the smallest orbital boosters to ever fly, closer in size and mass to the German V2 of World War II than the towering vehicles being built by SpaceX or Blue Origin. Even the Rocket Lab Electron, itself an exceptionally svelte rocket, is considerably larger.

The reason they’re trying to build such a small rocket is of course very simple: smaller means cheaper. Assuming you’ve got a payload light and compact enough to fit on their launcher, Astra says they can put it into orbit for roughly $2.5 million USD; less than half the cost of a dedicated flight aboard Rocket Lab’s Electron, and competitive with SpaceX’s “rideshare” program. Such a low ticket price would have been unfathomable a decade ago, and promises to shake up an already highly competitive commercial launch market. But naturally, Astra has to get the thing flying reliably before we can celebrate this new spaceflight milestone.

Their latest mission ended in a total loss of the vehicle and payload when the upper stage tumbled out of control roughly three minutes after an otherwise perfect liftoff from Cape Canaveral Space Force Station in Florida. Such issues aren’t uncommon for a new orbital booster, and few rockets in history have entered regular service without a lost payload or two on the books. But this failure, broadcast live over the Internet, was something quite unusual: because of the unconventional design of Astra’s diminutive rocket, the upper stage appeared to get stuck inside the booster after the payload fairing failed to open fully.

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Levitating With Light

February 23, 2022 by 31 Comments

The University of Pennsylvania has a team that did a little light research. Well, not light in the usual sense of that phrase. They used very strong light to levitate Mylar disks in a vacuum chamber.

Of course, it is no secret that light can exert pressure. That’s how solar sails work and some scientists have used it to work with aerosols and the like. But this appears to be the first time light lifted a large item against gravity. The team claims that their tests showed that a sunlight-powered flying vehicle might carry up to ten milligrams of payload. That doesn’t sound like much, but it’s impressive and the paper mentions that since the lift is not from aerodynamic forces, there might be applications in flying at very high altitudes.

The Mylar disks were 500 nanometers thick and had a 300 nanometer layer of carbon nanotubes beneath. The nanotubes absorb light, make the disks more rigid, and improve the Mylar’s surface-gas characteristics. The light source had a strong center beam and an even stronger ring around the center beam that causes the disk to remain over the center beam. The LED system used eight arrays, each consuming 100 watts of input power.

Preparing the disk might be difficult, but the LED power isn’t that hard. Even if you do like the researchers did and use water cooling.

Novena Open Source Laptop Reborn As Desktop Machine

February 23, 2022 by 35 Comments

When your 5-year-old laptop dies it’s usually time for a replacement. But [Andrew Menadue]’s Novena laptop is fully open-source. He has full access to all the documentation, so he decided to try his hand at repairing it instead. The power supply circuit board went up in smoke one day — he attributes this to poor battery health due to him not using it frequently enough. Given his usage pattern, he decided to switch the Novena into a desktop machine.

He made the conversion with a new pass-through power supply board, and the computer booted up but with no display. It seems that the power supply failure took out additional circuits as well. [Andrew] goes down a deep rabbit hole of board and chip swapping, all to no avail. Eventually the display suddenly springs to life, and he concludes the problem was with the EEPROM configuration settings and not LCD display hardware.

Experimenting with LCD Outputs on the Mainboard

It’s comforting to know that you can easily spin a replacement PCB for your computer when needed. But this situation is far from mainstream. Furthermore, all projects, open-sourced or not, face the issue of part obsolescence, even Novena. Back in 2019 founders [Bunnie] and [Xobs] issued an end-of-life announcement on the project’s five year anniversary for this very reason. The fact that Novena availability even lasted five years was due to up-front purchases of critical parts.

We wrote about the Novena way back in 2014, and more recently the MNT Reform project. What are your thoughts on these open source laptop projects? Do you have any laptops that you’ve rehabilitated after five or more years? Let us know in the comments below.

Winding Your Own Small Coils

February 22, 2022 by 18 Comments

Depending on what you build, you may or may not run into a lot of inductors. If you need small value coils, it is easy to make good-looking coils, and [JohnAudioTech] shows you how. Of course, doing the winding itself isn’t that hard, but you do need to know how to estimate the number of turns you need and how to validate the coil by measurement.

[John] uses a variety of techniques to estimate and measure his coils ranging from math to using an oscilloscope. He even uses an old-fashioned nomogram from a Radio Shack databook circa 1972.

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How Big Is The Moon? Figure It Out Yourself

February 22, 2022 by 4 Comments

We have to confess that we occasionally send friends a link to “let me Google that for you” when they ask us something that they could have easily found online. Naturally, if someone asked us how big the moon is, we’d ask Google or another search engine. But not [Prof Matt Strassler]. He’d tell you to figure it out yourself and he would then show you how to do it.

This isn’t a new question. People have been wondering about the moon since the dawn of human civilization. The ancient Greeks not only asked the question, but they worked out a pretty good answer. They knew approximately how big the Earth was and they knew the moon was far away because it is seen over a very wide area. They also knew the sun was even further away because the moon sometimes blocks the sun’s light in an eclipse. Using complex geometry and proto-trigonometry they were able to work out an approximate size of the moon. [Matt’s] method is similar but easier and relies on the moon occluding distant stars and planets.

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The AUO-manufactured controller board of an LG-branded TV. (Credit: Andrew Menadue)

What To Do With A Broken Television When You Can’t Fix It

February 22, 2022 by 31 Comments

Who can say ‘no’ to a free TV, even if it’s broken? This was the situation [Andrew Menadue] ended up in last year when he was offered an LG 39LE4900 LCD TV. As [Andrew] describes in the blog post along with videos (see first part embedded after the break), this particular television had been taken to a television repair shop previously after the HDMI inputs stopped working, but due to a lack of replacement parts the owner had to make due with the analog inputs still working. That is, until those stopped working as well.

The nice thing about these TVs is that they are very modular inside, as [Andrew] also discovered to his delight. In addition to the LG controller board, an inverter board and the power supply board, this TV also contained a TCON PCB. After some initial unsuccessful swapping of the parts with EBay replacements, nothing was (surprisingly) working, but it did turn out that the TCON and inverter boards are made and sold by AUO (major Taiwanese display manufacturer), along with the display itself.

In the end it turned out that the AUO boards and screen were fine, and after sourcing a board to convert VGA input to the LVDS signal accepted by the TCON board, the whole display worked. Naturally using a board with HDMI inputs would be nice, but it does show how a ‘broken’ TV can be turned into a really nice, big monitor without all too much effort if it’s just the controller board that went on the fritz.

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