Wednesday, March 17, 2010

Quixote's Nightmare

Quixote's Nightmare is an abstract ice sculpture that captures a view through the eyes of Don Quixote. Lars Hansen and I completed it as our entry in the Single Block Classic at the 2010 World Ice Art Championships. The piece was illuminated with white lights for judging the first night.

We returned a couple nights later to see the sculpture under colored lights. I like the colors the Ice Alaska lighting crew picked for us! Sculptors are encouraged to submit lighting design diagrams, but this year we decided to let someone else choose for us.

While we were there, I stupidly tried to brush some snow off of the wheel at the front of the piece. The left eyeball came crashing down! Fortunately this happened 48 hours after judging and after the official photos were taken, and ice sculptures are temporary anyway. I still feel bad, though. Here you can see the eye resting on the ground. It is a nice piece that Lars turned on the lathe. He also sculpted the interior of the eyeball with the boiler.

From the side you can see the linkage mechanism quite clearly. The piece was intended to be a working machine, a windmill whose rotor turns when the wheel on the front is turned, but the mechanism failed to function. last year's piece still stands as our most successful mechanical sculpture. Apart from the mechanical failure, we thought that this year's effort was a great success overall.

Quixote's Nightmare tells a story much more than any of our previous sculptures. We had a lot of fun figuring out how to bring the story to life both artistically and mechanically. I was particularly fond of the inscription we chose.

Tuesday, March 16, 2010

a $16 pocket spectrum analyzer

ShmooCon was, once again, a fantastic experience this year. One of many highlights of this year's event for me was hacking on some radio devices with Travis Goodspeed in the hotel bar for hours on end. This included playing with the IM-Me that he brought. As soon as I got home I ordered one. I found mine for $15.99 and free shipping on eBay.

Since then I've written custom firmware to turn my IM-Me into a pocket spectrum analyzer, shown here displaying activity of a frequency hopping system at a grocery store. The only change I've made to the hardware is the addition of a ribbon cable in order to easily connect to a GoodFET for programming, but this is simply creating a permanent connection to the debug contact points that are already exposed in the battery compartment. I've followed Travis's advice on how to develop for the platform.

The software tunes the IM-Me's radio chip to one frequency at a time, uses the chip's RSSI measurement function, and plots the result as one column on the LCD. It sweeps across the whole screen (132 columns) several times per second, showing a contiguous range of radio frequency activity. The technique works quite well, although there are a few defects. Most notably, harmonics of the IM-Me's 26 MHz crystal show up as spurs on the display.

The frequency ranges supported by my device are 281 - 361, 378 - 481, and 749 - 962 MHz. This is about 50% more than the chip is advertised to support and covers quite a bit of interesting activity in the US including ISM, LMR, television, amateur bands, pagers, and mobile phones. The edges of the bands supported by other batches of chips may differ but probably not by much.

The software supports three bandwidth modes: wide (default), narrow, and ultrawide. Wide mode displays 26.4 MHz of bandwidth in 200 kHz increments. Narrow mode displays 6.6 MHz of bandwidth in 50 kHz increments. Ultrawide mode, shown here with some mobile phone activity, displays 88 MHz of bandwidth in 667 kHz increments.

The code is open and available here. I'd love to hear from you if you give it a try. Huge thanks to both Travis and Dave who did the hard reverse engineering work!

Update: The code has a new home at github.