Chris Eckert, a San Jose artist, has been working up on “Gimme” – a prototype for a pan-handling sculpture. It is controlled by Arduino Pro Mini, a microcontroller board based on the ATmega168 that utilizes sensors to track the movement of a person, and once they are found, the sculpture automatically solicits money.
Gimme’s stepper motors are driven by Pololu A4983 Stepper Motor Driver Carriers. The stepper drivers, sensors and microcontroller are all embedded on a custom circuit board designed with Eagle CAD.
The key element that will interest other designers is its use of sensors. Chris Eckert said: “I want rudimentary motion tracking over 180 degrees so my first setup was a static array of five sensors. My idea was that, as an object moves past these five sensors, one or more would register a distance. Interpreting this information with an Arduino micro-controller, I could roughly point toward the object.”
“Simple idea but it got a little more complicated. The difficult thing about the sensors I’m using it that their output falls off exponentially with distance; objects farther away produce a MUCH smaller sensor change than objects close up. To get an approximately accurate distance from these sensors, I had to linearize the sensor outputs – lots of math. Took a while but I finally got it working well.”
When Mr. Eckert found “holes” in Gimme’s sensor pattern where none of the sensors can see the person standing on these “holes”, he tried a different approach, instead of increasing the number of sensors to process.
”Rather than having static sensors, I thought I’d sweep the sensors. I attached three sensors to a servo and slowly swept them back-and-forth. If any of the sensors detect an object, they move the three sensor array so that the centre sensor has the smallest distance. Voilà – motion tracking,” he added.