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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An analog multimeter being used as a ping display

Classic Multimeter Tells You If Your WiFi’s Working

February 22, 2022 by 14 Comments

Debugging network issues isn’t easy; many a sysadmin has spent hours trying to figure out which of the many links between client and server is misbehaving. Having a few clear pointers helps: if you can show that the internet connection is up, that already narrows down the problem to either the server or, most likely, the client computer.

After hearing “is the internet up” one too many times, [whiskeytangohotel] decided to make a clearly visible indicator to show the status of the local uplink. He used his father’s old Simpson 260 VOM as a display, with its large analog indicator pointing at a steady value if the internet’s up, and wagging back and forth if there’s an outage. The exact value indicated is determined by the average ping time for a couple of different servers, so that you can also tell if the connection is slower than normal.

The ping times are measured by an ESP8266 connected to WiFi, which checks a predefined list of web servers and calculates the average ping time every fifteen seconds. An analog value in the 2.5 V range is then generated and measured by the meter. The smooth motion of an old analog meter stands in nice contrast to the modern-day problem of unstable WiFi.

While analog multimeters definitely have their uses, we’re the first to admit that our classic meters don’t see as much action as they could. Repurposing them as [whiskeytangohotel] did is a neat way of keeping those heirlooms around for the next generation. Of course, if you don’t have an analog multimeter, you could also use an analog clock for your ping meter. Continue reading “Classic Multimeter Tells You If Your WiFi’s Working” →

Bend Your Vase Mode Prints By Hacking The GCode

February 22, 2022 by 3 Comments

[Stefan] from CNCKitchen wanted to make some bendy tubes for a window-mountable ball run, and rather than coming up with some bent tube models, it seemed there might be a different way to achieve the desired outcome. Starting with a simple tube model designed to be quickly printed in vase mode, he wrote a Python script which read in the G-Code, and modified it allow it to be bent along a spline path.

Vase mode works by slowly ramping up the Z-axis as the extruder follows the object outline, but the slicing process is still essentially the same, with the object sliced in a plane parallel to the bed. Whilst this non-planar method moves the Z-axis in sync with the horizontal motion (although currently limited to only one plane of distortion, which simplifies the maths a bit) it is we guess still technically a planar solution, but just an inclined plane. But we digress, non-planar in this context merely means not parallel to the bed, and we’ll roll with that.

[Stefan] explains that there are quite a few difficulties with this approach. The first issue is that on the inside of the bend, the material flow rate needed to be scaled back to compensate. But the main problem stems from the design of the extruder itself. Intended for operating parallel to the bed, there are often a few structures in the way of operating at an angle, such as fan mounts, and the hotend itself. By selecting an appropriate machine and tweaking it a bit, [Stefan] managed to get it to work at angles up to 30 degrees off the horizontal plane. One annoyance was that the stock nozzle shape of his E3D Volcano hotend didn’t lend itself to operating at such an inclination, so he needed to mount an older V6-style tip with an adapter. After a lot of tuning and fails, it did work and the final goal was achieved! If you want to try this for yourselves, the code for this can be found on the project GitHub.

If you want to learn more about non-planar printing, we’ve covered the process of non-planar slicing a while back, and if you think your 2.5D printer doesn’t quite have the range for really funky print paths, then you may want to look into a robot arm based printer instead.

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