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

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:<p><a href="https:&#x2F;&#x2F;cs.nyu.edu&#x2F;~jhan&#x2F;ledtouch&#x2F;index.html" rel="nofollow">https:&#x2F;&#x2F;cs.nyu.edu&#x2F;~jhan&#x2F;ledtouch&#x2F;index.html</a><p>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:<p><a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28475474" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=28475474</a>

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.

Made me think of Eli Yablonovitch, “A great solar cell also needs to be a great LED.” RIP Alta Devices.<p><a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=u_K1URyarE0" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=u_K1URyarE0</a>

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

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.