4 ms·

Using a laser pointer and a matrix LED as a two-dimensional input device (2010)

83 points by rsre 5y ago

atoav 5y ago
Very cool, I was not aware that LEDs could be used like that. I wonder how sensetive this technique can get.
- a9h74j 5y ago
  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 5y ago
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 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 https://news.ycombinator.com/item?id=28475474
- shreddit 5y ago
  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 5y ago
    Just swap a couple of pipes to reverse the heat pump. Nothing can possibly go wrong.
    - spijdar 5y ago
      ...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 5y ago
        You will be able to reach small ~100°C 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 5y ago
        Is the problem "literally using a freezer"? Could you (in principle) build an insulated chamber that could deal with the temperatures?
        marcosdumay 5y ago
        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).
    - 5y ago
- _spduchamp 5y ago
  I've wondered how hard it would be to hack old LED signs into OSC touch control surfaces.
  - elcritch 5y ago
    What about modern OLED tv’s? It’d be fun to have a 50” touchscreen.
nayuki 5y ago
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 5y ago
  Note quite. See [1] [1] https://www.arduino.cc/en/Reference/PortManipulation https://www.arduino.cc/en/Reference/PortManipulation
  - kaszanka 5y ago
    Yes, Arduino is the library that defines these macros: https://github.com/arduino/ArduinoCore-avr/blob/8f8df161ebf3d8bc595d226c3d3a9125383042a5/cores/arduino/binary.h https://github.com/arduino/ArduinoCore-avr/blob/8f8df161ebf3...
baking 5y ago
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 https://www.youtube.com/watch?v=u_K1URyarE0
helpm33 5y ago
BBC Micro:bit has a 5x5 LED matrix that can be read by an analog GPIO, so you can play with reading back light levels.

83 points by rsre 5y ago

atoav 5y ago

Very cool, I was not aware that LEDs could be used like that. I wonder how sensetive this technique can get.

a9h74j 5y ago
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 5y ago

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 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 https://news.ycombinator.com/item?id=28475474

shreddit 5y ago
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 5y ago
  Just swap a couple of pipes to reverse the heat pump. Nothing can possibly go wrong.
  - spijdar 5y ago
    ...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 5y ago
      You will be able to reach small ~100°C 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 5y ago
        Is the problem "literally using a freezer"? Could you (in principle) build an insulated chamber that could deal with the temperatures?
        marcosdumay 5y ago
        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).
  - 5y ago
_spduchamp 5y ago
I've wondered how hard it would be to hack old LED signs into OSC touch control surfaces.
- elcritch 5y ago
  What about modern OLED tv’s? It’d be fun to have a 50” touchscreen.

nayuki 5y ago

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 5y ago
Note quite. See [1] [1] https://www.arduino.cc/en/Reference/PortManipulation https://www.arduino.cc/en/Reference/PortManipulation
- kaszanka 5y ago
  Yes, Arduino is the library that defines these macros: https://github.com/arduino/ArduinoCore-avr/blob/8f8df161ebf3d8bc595d226c3d3a9125383042a5/cores/arduino/binary.h https://github.com/arduino/ArduinoCore-avr/blob/8f8df161ebf3...

baking 5y ago

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 https://www.youtube.com/watch?v=u_K1URyarE0

helpm33 5y ago

BBC Micro:bit has a 5x5 LED matrix that can be read by an analog GPIO, so you can play with reading back light levels.