Lindy Mayfield wrote:
> On Olin's page there is a cool spinning row of LEDs that show text.  In
> this application, how does the PIC know the exact position of the
> motor/row of led's?

There is an opto-interrupter mounted on the bottom of the rotating board,
and a piece of metal sticking up from the stationary part the interrupts the
beam once per rotation.  That pulse is captured with a CCP module on a
16C66, and the rest is all Firmware Magic (tm).

The one you see a picture of has 16 T1 3/4 LEDs vertically.  The new version
has 96 RGB LEDs and can put up recognizable pictures of people's faces.  The
data rates are rather higher as you can imagine, but the rotation tick is
handled in pretty much the same way.  The new ball has 3 dsPICs and one 18F
PIC.  One dsPIC runs the power supply, one does vector font to pixel
rendering on the fly, and the third is on the rotary board moving the data
around and driving the FPGA which does high speed updating of the LEDs
including PWM to achieve 4 levels of brightness per pixel per color.


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