[HN Gopher] Using a laser pointer and a matrix LED as a two-dime...
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Using a laser pointer and a matrix LED as a two-dimensional input
device (2010)
Author : rsre
Score : 76 points
Date : 2021-09-10 10:23 UTC (2 days ago)
(HTM) web link (www.cs.cmu.edu)
(TXT) w3m dump (www.cs.cmu.edu)
| nayuki wrote:
| I see they did a trick in the code: Because binary literals were
| added late in C++14, it seems they used some library which
| defined 256 constants like B00000000 = 0, B00000001 = 1, ...,
| B11111111 = 255.
| Moosdijk wrote:
| Note quite. See [1]
|
| [1] https://www.arduino.cc/en/Reference/PortManipulation
| kaszanka wrote:
| Yes, Arduino is the library that defines these macros:
| https://github.com/arduino/ArduinoCore-
| avr/blob/8f8df161ebf3...
| atoav wrote:
| Very cool, I was not aware that LEDs could be used like that. I
| wonder how sensetive this technique can get.
| a9h74j wrote:
| People have made half-duplex, 2-way single-fiber links this
| way.
|
| With reverse-biased diodes, you are operating in
| photoconduction mode. If tightly-coupled to a fiber optic, and
| with a quantum efficiency of say, 10%, that would mean for
| every 10 photons which come in, you get 1 electron charge of
| current flow.
|
| IIRC there are people who paint e.g. 1N4444 diodes with black
| paint to minimize opto-induced leakage.
| _Microft wrote:
| You might also want to watch this video that demonstrates a 2D
| proximity sensor using an LED array. It works without a laser
| pointer, using the fingertips alone is good enough for it:
|
| https://cs.nyu.edu/~jhan/ledtouch/index.html
|
| A few days ago, a user here also commented on how LEDs work both
| ways and how he used this effect to automatically adjust the
| brightness of an LED to ambient light. You can find that comment
| here:
|
| https://news.ycombinator.com/item?id=28475474
| _spduchamp wrote:
| I've wondered how hard it would be to hack old LED signs into
| OSC touch control surfaces.
| shreddit wrote:
| Very impressive, i love this kind of stuff.
|
| "...and in my next video I'll show you how to bake a pizza in
| your freezer."
| nayuki wrote:
| Just swap a couple of pipes to reverse the heat pump. Nothing
| can possibly go wrong.
| spijdar wrote:
| ...okay, but could this actually work? I'm assuming because
| there are no products like this that there's a giant caveat
| somewhere, but isn't it actually a good idea?
|
| My understanding is heat pumps can move more heat energy
| in/out of a system than the electrical energy input into
| them. My peabrain logic thinks, "Wait a moment, doesn't
| that mean a heatpump oven would be more energy efficient
| than a conventional electric oven with resistive heating?"
|
| I'm assuming the problem lies somewhere in refrigerants
| not, uh, behaving well at oven temperatures?
| marcosdumay wrote:
| You will be able to reach small ~100degC heating before
| everything starts failing and getting on fire, then you
| will get much larger temperatures, once. If you have a
| bad enough circuit breaker, you may even reach
| metallurgic oven temperatures for a short while!
|
| The refrigerant gas failing isn't actually a problem for
| high temperatures. They are a problem to getting too
| cold, but if you get hot enough, anything will work. Even
| if it burns down inside your pipes, the results will
| still work (but your pipes won't).
| spijdar wrote:
| Is the problem "literally using a freezer"? Could you (in
| principle) build an insulated chamber that could deal
| with the temperatures?
| marcosdumay wrote:
| Ok, the question is if you could build an oven heated by
| a heat pump? Yes, you could.
|
| You can reach home cooking temperatures reasonably
| easily, and probably even large ones. It's helpful that
| the compressor only has to deal with gases after they got
| cooled and heated again on the open air, all the really
| hot parts are rigid tubing.
|
| There will be problems turning the compressor off,
| dealing with the heat that propagates back through the
| pipes. You can solve them with some usual cooling devices
| (heat disipators, fans, etc).
| marcosdumay wrote:
| It has a way to push heat into it, some heat insulation, a
| door, and it's food-ready. The thing is basically an oven
| already, and 270K and 400K are just some 30% change.
| baking wrote:
| Made me think of Eli Yablonovitch, "A great solar cell also needs
| to be a great LED." RIP Alta Devices.
|
| https://www.youtube.com/watch?v=u_K1URyarE0
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