iliis

There's actually a quite nifty principle that makes it relatively easy to build your own multitouch table: Frustrated total internal reflection.

The idea is based on internal reflection: Whenever lights hits the boundary between two materials with different density it gets refracted. If it goes from dense to less dense and the angle is flat enough it will reflect back. This is the principle behind fibre optics. It's also the reason why the water's surface looks "silvery" (like a mirror) when you're submerged and look up at an angle (i.e. not straight up).

Now imagine you have a plane of glass and you put LEDs around the edges that shine into it from the side. The light will zig-zag trough the glass and come out at the other edge. However, if you touch the glass you inhibit that total internal reflection because your finger is alot denser than the air and so the light will "leak" out the glass where you touch it, illuminating your finger. If you look at the glass from behind you'll see a bright spot.

Use a camera to detect that spot and you basically have a touchpad. To make it a screen you can put a translucent sheet behind the glass and project an image onto it (and use infrared LEDs).

See e.g. http://wiki.nuigroup.com/FTIR for some helpful images. Just google "FTIR touch screen" or similar for build instructions and blob-detection software.

What a fun question :) And there are some very cool answers!

A few things that come to mind from my life, from back when I was still a kid/teenager:

- Building a three-way marble-track switch. There are many marble tracks that have these two-way switches that alternate between two tracks, like this one here: https://theworkbenchutah.files.wordpress.com/2013/04/06-marb... I wanted to build one that would evenly distribute marbles along three tracks. Took me quite a few prototypes until I finally had a working one. And all I had to work with was paper, tape, glue etc. No wood or metal, no bearings or precision mechanics, only a kid's craft stuff.

- A LEGO technics robot leg. This is a bit hard to explain without images. I wanted to build a legged robot (something spider-like) and needed legs that could move a foot both borward and back and also up and down. As the LEGO motors where quite big and heavy I didn't want to mount them on the leg itself (e.g. at the "knee") but have them all fixed inside the body and transmit their power via gears and shaft. The problem here was, that the up-and-down-motion had to go trough the forward-and-back-joint which meant that whenever the leg moved forwards or backwards it would also move a bit up or down, even if the up-and-down-motor didn't move at all. So I wanted to decouple these two motions. This would be trivial to do in software but I was just a kid playing with LEGOs so I wanted a mechanical solution. I managed it by using a mechanical differential to actually subtract the one motion of the other. Unfortunately, I then realised I didn't have enough motors for a full robot...

- Years later I was learning C++ and I wanted some kind of "linked variables" (I'm sure there's an official term for this): I.e. variables that would depend on others and would update whenever one of their dependencies changed. I though this would be a cool way of writing a GUI. With a lot of operator overloading and some abuse of the type system I could actually write things like

    x = a + b * 2;
    y = x / b;

And 'y' would update whenever a or b (or x) was changed.

I'm not sure if they really are the hardest problems I've ever solved, but it certainly felt so at the time ;)

So... Five stars then? ;)

(But seriously, HN comments are actually great at recommending things.)

About those sneakers: https://www.thingiverse.com/thing:285404 ;) But yeah, I agree that there's much too much hype around a lot of stuff...

Well, okay. Technically you're right ;) But what if you count any movements that are followed by another movement of the same face as a single step?

That might very well be, but is it obviously so? What if there was a position that takes 19 moves to solve in the fastest way possible but the next-best solution takes 21 moves? Is there always a solution that takes an even number of steps?

Did you try NewPipe? It works without the Google services and offers a few nifty features like background-play. https://f-droid.org/en/packages/org.schabi.newpipe/

There was a similiar case in South Africa, where SIM cards were stolen from traffic lights and also racked up large bills: https://www.bbc.com/news/world-africa-12135841

You could, but it would be thermally quite bad: The only way for parts to cool would be through radiation, which is way less effective than convection (be it forced by fans or passive, as in OP's design.)

That's actually a good idea! It doesn't work for Google or Facebook tough, or other services I explicitely don't log right back in.

If it is well integrated with your browser it's quite ok. Maybe not as convenient as using the same simple password everywhere but certainly a lot better than having to remember a lot of different passwords ;)

Which is exactly what I'm trying to avoid. I don't want to be tracked so I try to limit the amount of fingerprinting possible.

How about a password manager?

Or even better: Some kind of hardware token and a good standard that goes with it?

No, please don't. This is arduous for those of us who like a bit of privacy and regularly clear their cookies etc.

Well, in that case a non-textured or reflective clothing could have a similar effect.

It seems that this is directly caused by the arctic temperature rise: https://en.wikipedia.org/wiki/Sudden_stratospheric_warming

Relevant quote: Following a sudden stratospheric warming, the high altitude winds reverse to flow eastward instead of their usual westward. The eastward winds progress down through the atmosphere and weaken the jet stream, often giving easterly winds near the surface and resulting in dramatic reductions in temperature in Europe.

see also (in german): http://www.meteoschweiz.admin.ch/home/aktuell/meteoschweiz-b...

live view of Starman and his car: https://www.youtube.com/watch?v=aBr2kKAHN6M

Live view of Starman in orbit: https://www.youtube.com/watch?v=aBr2kKAHN6M

We mainly do SMT at our hackerspace, as it is really is fast and easy to do by hand using a hot-air gun (e.g. [1]). Use a syringe to deposit solder paste (we have one which uses compressed air, very convenient! Something like [2]) and a binocular to see what you're doing and you will be golden.

[1] http://www.aoyue.eu/aoyue-int998-smd-rework-station-hot-air-... [2] https://www.aliexpress.com/item/220V-AD-982-Semi-Auto-Glue-D...

Another method is to use a high-powered pulsed laser to create little balls of plasma in mid-air: https://www.popsci.com/secret-interactive-holograms-plasma-a...

Awesome achievement! This really looks like a viable way of true floating 3D-images.

Can you levitate multiple particles at the same time? How fast are they moving? How sensitivie is it to disturbances in the air?

More details in this german article: https://www.golem.de/news/kilopower-ein-kernreaktor-fuer-rau...

I'll summarize some of the interesting points:

- The nuclear core (75kg of enriched uranium/molybdenum [1]) is designed to not go critical, even if it accidentally falls into the sea and is surrounded by water (which is a good neutron reflector). It only starts when you surround it with a neutron reflector made of beryllium (an even better neutron reflector, mainly due to less absorbtion). Combined with the fact that the reactor only gets nasty when it's been running for a while (and thus is already far away from earth) it is a lot safer than plutonium fueled RTGs.

- It would be very useful to reach far away destinations (like the orbit of Uranus, Neptun or Pluto) using ion drives, as they need to run for years and solar panels aren't effective far away from the sun.

- While there have been other attempts at developing nuclear reactors for space, most of them didn't go far. They could use an existing research reactor (Flattop [2]) for this project which already has all the required permissions to run, so a lot of paperwork could be saved for the Kilopower experiments.

- The Kilopower reactor is the first to use heatpipes instead of pumps for the heat transport and stirling engines for the energy generation. The first experiment was thus to show that the cyclic heat draw of the stirling engine would be safe, because usually nuclear reactors reach an equilibrium between heating up (and thus expanding slighty which slows down the reaction) and cooling down (which accelerates the reaction).

- Instead of the planned eight 125W Stirling engines, they're currently using two 70W ones from the Advanced Stirling Converter Project [3]. The other ones will be simulated using simple heatsinks.

- Theoretically it could run for hundreds of years (after 500 years less than 1% of the uranium will be used), but the Stirling engines will break much sooner than that.

[1] http://www.iaea.org/inis/collection/NCLCollectionStore/_Publ...

[2] https://en.wikipedia.org/wiki/Flattop_(critical_assembly)

[3] https://tec.grc.nasa.gov/rps/stirling-research-lab/advanced-...

Actually, the link is just wrongly formatted, the HSLuv project is online: http://www.hsluv.org/

Why the hack? I think you can switch to the old graphics in the remastered version. Or does that switch voices too?

Not all that directly related, but if you like these old adventures and don't know it yet then check out ScummVM! It's an open source project allowing you to play all these games on more or less any modern device (including Linux, Android, iOS etc.)

They also have a few awesome games freely available under http://scummvm.org/games/, for example "Beneath a Steel Sky" (which I'm playing right now, probably for the fourth time or so ;)) or "Flight of the Amazon Queen".

Ha, yes, definititely! Did you ever come into contact with RF design? Things like antennas are quite literally drawing-pentagrams-on-the-floor-style witchcraft ;) [1]

You might also like [2], a story where magic is real and treated as just another field of science/engineering (yes, there are ISO standards for your magic circles and everything ;).

---

[1] See e.g. https://www.sv1afn.com/pcbruler.html or http://www.digdice.com/wp-content/uploads/2008/08/panel22dbi... for some examples.

[2] https://qntm.org/ra