IM-Me Spectrum Analyzer

Monday, February 28, 2011 by darco
Posted in

narrow At some point I ran across Travis Goodspeed's fascinating blog, and after some poking around I found his post about hacking the GirlTech IM-Me toy. Curious, I did some googling and found Michael Ossmann's $16 Pocket Spectrum Analyzer. At that point I make a realization. I must have one.

But... It's so... Pink. So... I plasti-dipped it.

IMG_1539

As you can see from the debug header, it is still a work in progress. This is my first attempt to use plasti-dip as a device coating, so some parts didn't turn out quite as well as I had hoped—but at least it doesn't reek of a tween-age girl's toy.

Just to prove that this device is in fact now a sophisticated scientific instrument and no longer a toy, here is a picture of it showing my iPad's 3G signal as it loads John Gruber's blog:

IMG_1543

The firmware is largely unmodified from Michael's original release, but I did make a few tweaks to suit my taste.

Backlight

First, with the stock toy firmware, the backlight actually turned off when you pressed the power button. With Michael's firmware, the backlight remained on—wasting power. After some poking around I found that the backlight can be controlled via pin P2.0. Pulling this pin low will disable the backlight. You can also duty cycle P2.0 to adjust the brightness of the backlight.

Keeping State

Michael's firmware also annoyingly always reset itself whenever you press the power button to turn it on. Also, the max-hold mode was always reset whenever you moved the window left or right. A quick modification allows the device remember its last state on power-up and also make the max-hold mode sticky.

At some point I'll add these changes to my own SVN repository and make them available for others to use.

Uses

So what am I going to use this thing for anyway? Well, most of my home-automation network will be on 2.4GHz, but some parts may end up being in the 900MHz range. This tool would be useful for debugging these devices. It's also useful for just snooping around to see what is transmitting around us. Baby monitors, wireless alarm systems, smart meters, etc...

With some firmware updates, I should be able to demodulate some signals and actually display what is actually being transmitted (instead of just showing that something is transmitting, which is what it currently does).

More Info

If you are interested in getting one of these devices to hack on, you should have a look at Dave's first article about IM-Me hacking. Without Dave's initial work to get the ball rolling and generate general interest in hacking this device, we may have never known the wonders of the $16 spectrum analyzer.