The Haptic Compass

Last night I built a haptic compass, also known as the Clown Belt. This is a belt which features twelve vibrating pager motors equally spaced around the perimeter of the belt. The control box uses a digital compass to determine which way is north, and continuously buzzes the appropriate motor. The effect is subtle but noticeable. I feel like I’ve been granted a strange new sense of direction.

The belt has additional features: it can be connected via serial to my iPhone which delivers up a bearing to an arbitrary destination. I have a first generation iPhone, which means my current location is highly approximate, but for distant locations it works great.  It can also be controlled wirelessly over an XBee RF link, but the peculiar application of that is the subject of a future post.

As I excitedly show this device off today, people stare incredulously at me and ask “WHY?” I’ve wanted one of these devices ever since I read this wired article.  I just read it again, and it does an excellent job of explaining why I built this device.

“It was slightly strange at first,” Wächter says, “though on the bike, it was great.” He started to become more aware of the peregrinations he had to make while trying to reach a destination. “I finally understood just how much roads actually wind,” he says. He learned to deal with the stares he got in the library, his belt humming like a distant chain saw. Deep into the experiment, Wächter says, “I suddenly realized that my perception had shifted. I had some kind of internal map of the city in my head. I could always find my way home. Eventually, I felt I couldn’t get lost, even in a completely new place.”

I have an excellent sense of bearing and direction.  I don’t get lost, and I can always point west, owing to having lived most of my life near a west coast beach.

Why do I have this sense?  Is there a biomechanical support for this sense? Are humans equipped with some absolute magnetic sense: a special sensor like a bird’s nose magnet that I can tap into more effectively than others?

Or is my internal compass merely a highly integrated relative sense?  If I drive around in a car, I change orientations at a slow enough rate that I can integrate my current bearing.  If I spin quickly in place, I’ll get disoriented.  If I’m wearing a blindfold while I spin, I probably lose my bearings (and lose track of the piñata).  That suggests there is no biomechanical compass I can read directly, but rather that I’m subconsciously integrating many directional cues from sound and sight and feel.

These two possibilities suggest two very different outcomes for my experiment of wearing this belt for awhile:

  • If this is an absolute sense, then the haptic compass will reinforce this sense.  I will, in essence, be engaged in reinforcement learning.  Once the experiment ends, I expect that I will have a better sense of bearing both in places I visited while wearing the belt and in places I didn’t visit, because my inherent absolute sense of direction will have been “trained up.”
  • If this is a relative sense then I’m screwed.  The additional input of the belt will overwhelm the other senses I use to reckon bearing.  When my Mom got a car with a GPS navigator, she stopped paying attention to where she was driving.  That will happen to me at a far more basic level.  Personally, I believe this is the more likely scenario.

Now some technical details.  The belt has twelve shaftless vibration motors spaced equally along its length (around my perimeter?)  The motors are epoxied to a 14 conductor ribbon cable.  They connect electrically by plugging in to the ribbon crimps spaced along the cable.  The control box contains a Sparkfun Funnel IO arduino board, which has a built in XBee socket and LiPO charger IC on board (excellent!).  The box also contains a I2C Honeywell compass module.  Its powered by a LiPO battery.  Everything is precision-electrical-taped to a custom PodBelt blank graciously provided by Isa (Psymbiote.)

The haptic compass is something I’ve wanted since I read the Wired article linked above.  And though it took me two years to motivate, once all the parts had arrived it took me exactly 24 hours to build this entire project.  I love Arduinos for the ease with which I can make physical devices operate and communicate.

north