THE POSITION CONTROLLER FROM PARALLAX.
This month, we have the pleasure of presenting the Position Controller Kit from Parallax. In the tradition of Parallax products like the Scribbler robot, the position
controller is easy to implement, a breeze to program, and is
versatile enough to keep novice and expert roboticists
engaged and entertained. We thought a good way to test
the module’s accessibility was to implement it with the
classically hackable Scribbler in a project that could appeal
to even less experienced members of the SERVO Nation.
The Run Down
The position controller is designed to take over wheel
operation functions that would otherwise require the
attention of the robot’s microcontroller. The position
controller can impressively be interfaced with any
microcontroller, and it can also be used in
conjunction with HB- 25 motor controllers to help
control 12 VDC motors. But even without acting as a
motor controller, the position controller can perform
a host of useful functions. The most apparent use
without the motor controller is to use the position
controller as an encoder to measure speed and
The position controller uses optical interrupter
switches to sense the position of a handy encoder
wheel that comes with the kit. The encoder wheel
has nine fins, but because the optical interrupter
switches make measurements at four positions, it can
sense 36 positions for one rotation of the wheel. The
documentation for the kit says that this corresponds
to about 0.5 inches of travel per position reading
using a six inch wheel. For young hackers wondering how
the good folks at Parallax came up with that number, they
can be introduced to the immortal equation of s = rθ.
THE PCB IS LABELED FOR YOUR CONVENIENCE.
SERVO 07.2010 71