Hello,
Im new to this forum and i dont know if this subject has been covered before but i just had to share it as i think it's coolest thing i've ever seen

We all know LED's emit light, did you know they can be used as a photodiode too?

I've read the theory, tryed it and yes it works, the theory is simple to understand if you are familiar with rc time

Take a look at the video here
http://mrl.nyu.edu/%7Ejhan/ledtouch/index.html

then read the theory here
http://www.merl.com/reports/docs/TR2003-35.pdf

im sure you'll be amazed too, or mabey im just easily pleased, if anyone has difficulties in coding the theory im quite willing to share my own code written in ASM & Proton