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Issue #224 March 2009

Vision-Guided Robotics
A Next-Generation Balancing Robot
by Hanno Sander

Start | Parallax Propeller | ViewPort | The DanceBot | Frame Grabber | Real-Time Tracking | Line Following With A Camera | Track A Pattern | Find A Beer Bottle | Wrap Up | Sources & PDF

PARALLAX PROPELLER

I started my project after my dad gave me a Parallax Propeller for Christmas. Parallax is best known for its Boe-Bot robot and BASIC Stamps, but its Propeller chip is quickly becoming popular with engineers and hobbyists because of its power and simplicity. Its eight identical processors (cogs) share common resources, such as global memory and an I/O port, but each can run its own program. It was perfect for my application because I needed to sample many different sensors at different rates, perform intensive filter calculations, process captured video, and control motors. I focused on parts of the problem and later integrated everything by assigning different algorithms to their own cogs.

The Propeller has eight 32-bit processors running at up to 80 MHz. It has shared global resources, including 32 KB of RAM, 32 KB of ROM, and 32 I/O pins. It has dedicated resources per processor, including 2 KB of RAM and two general counters, and video output. The Propeller operates at 3.3 VDC (each pin can sink up to 40 mA). It is available on Parallax’s web site for $12.99 per chip and $29.99 per ProtoBoard.

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