22 April 2009

LED Photos

OK, this one isn't really a project. But I wanted to share it anyway. One day a bought this little ...light thingy in a junk shop. I didn't really know what it was, but it had LEDs and anyway it was only 1 €...

This is what it looks like:

It turns out that it has three very bright LEDs in red, green and blue and it works in different modes; one of them is a colour change mode. But it does this by using a PWM scheme. So when you swing it around fast enough, you see circles in different colours.

And when I got my new camera with a night shot mode that allows to do an 8 second exposure time, I had to try photographing this. The pictures turned out quite well.

Musings on Charlieplexing

Some time ago I stumbled over an article about charlieplexing on hackaday.com. Charlieplexing is basically a method to control n * (n-1) LEDs using only n I/O ports of a microcontroller. Say you have 5 I/O ports, then you can control 5 x 4 = 20 LEDs independently! Find more details in Wikipedia. I was fascinated, because I had never thought it was possible to control so many LEDs with so little hardware.

But it seems that charlieplexing comes with a few drawbacks. While this is certainly true, some of these drawbacks are in my opinion over-emphasised, especially when compared to "conventional" LED multiplexing. So I set out to explore the issue, just for the fun of it.