The Nano POV

The Micro POV was about making a really small POV display. I wanted it to be as small as I possibly could make it. And it is small. But when I wrote my post about it, a thought struck me: It can be even smaller. I had used a AVR tiny24 controller, which only has 14 pins. But I could also have used a tiny25, which only has 8 pins (including VCC, GND and reset) and still could control 8 LEDs. How is that possible? Simple: By combining the current saving technique from the Micro POV with the LED multiplexing technique of the matrix display I made. To operate the Micro POV I had used a scheme were always only one LED gets activated at a time. This makes the device perfectly suitable for using charlieplexing. And since I wanted to control 8 LEDs I needed only four I/O ports to do this. This was the birth of the Nano POV.

The Micro POV

Electronics design in my opinion is the art of finding the best compromise. And this can be quite a complex art. There are many different and sometimes contradicting requirements to a project: Cost, time, space, weight, power, technology, market, availability of materials and tools, knowledge. This is why the all singing all dancing solution isn't always a good solution. Sometimes less is more. And I don't know why that is, but I have a special affection for minimalistic solutions.

I know, there are POV projects on the net in abundance. And most of them are some kind of propeller clock. There are a few really nice examples and I wanted to have one. I even started to build such a work of art and it was going to be really great with lots of colour and such. But very soon I gave up, because I just don't have the skills or equipment to build more complicated mechanical objects.

I realised that I had to reduce my expectations - a lot. And looking at various projects that I found on the net, I decided that maybe I should go for something really ... compact. And so the idea for a micro POV was born.

The name is of course a reference to the open source project MiniPOV by ladyada. But I wanted to go one step smaller - something to wear e.g. on the wrist. Of course that generates a few problems, which is just what made the whole thing the more interesting. Every component for this project needs special attention.

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.