I once had a co-worker whose side project was a little wireless weather station transmitter (back in the late 90s). He was getting reports of the batteries draining in a matter o days, when in testing (and in theory) they should last months.

After a lot of head scratching he discovered that the bit-change operation on the I/O port of the chip he was using was doing a read-modify-write routine. One of the pins on the I/O port (intended to be "write-only") was attached to a status LED.

In bright sunlight, the status LED was generating enough power to read high on the I/O port, so any unrelated bit flips on the port could cause the LED to turn and remain on in bright sunlight.

Jeff Han demonstrated this concept a few years ago, but without the laser: http://cs.nyu.edu/~jhan/ledtouch/index.html

I tried to wire one up myself but couldn't get it to work. I think certain LED matrixes don't work as well (maybe translucent vs transparent LEDs)

I wonder if one could combine a webcam and a projector for a "doodling" application? The rectangle of the bright white screen could be used for calibration. The software would look for a particular shade of red or green within that rectangle, and re-project at that spot.

Something like this? http://www.graffitiresearchlab.com/blog/projects/laser-tag/

Heh, I've got exactly this app sort of half working on my Pandaboard. I've been fighting the gstreamer API a bit in a non-X11 config.

Do you have more info? I have some architects (the physical building type) I am working with whom are very interested in such applications.

Can you show me what it is you have/are doing?

It's my intention to post it to Github, I've been going back and forth with the Texas Instruments folks on the Pandaboard group to figure out the best way to do graphics without X (and DirectFB wasn't working out for me, Wayland would rock but its not there yet). Assuming my experiments with that are successful I'll get the drawing side of things up sooner, then work the camera side.

Note that the only reason its taking me this long is because I'm trying to be cheap cheap cheap. You can do this with a laptop running OCV connected to a projector pretty easily. (although the first time you try this like I did, the feedback is really really trippy :-)

This is really cool, and ch00f does quite a few cool projects that pop up on reddit all the time.

Yeah, that's how I found his work. Saw a post of his on /r/cableporn last night and ended up going through a bunch of his blog.

Very clever!