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Chapter 01

Page 2

Propeller PCB

As the name suggests, it is the PCB which rotates (at high speed). It contains the visual-elements, the RGB LEDs. The persistence of vision is created by the rotating propeller. The LEDs are soldered on it in a linear fashion. This propeller PCB is plugged (connected) to an Arduino board like an Arduino Shield.

The Propeller PCB is shown bwlow:
LED Numbering
Two thing must be noted :
1) There is considerable gap between LEDs
2) The LEDs are numbered in a special way:
     14 12 10 8 6 4 2 0 1 3 5 7 9 11 13

This LED numbering system and the gap might seem unduly complicated.
Consider the case where there is simple numbering and there is no gap between the LEDs, as shown below:

Simple numbering

As you can see, each LED has an opaque black boundary, inside which there is a round transparent window (shown in white) from which light may pass. The light emmiting circular window, on the LED, is surrounded by an opaque boundary. When multiple LEDs are placed together linearly, then the gap between two round windows is significient. The image shown below is magnified to illustrate the probelm.

Gap between round windows
The following images illustrates the problem arised by simple linear numbering system.
All LEDs connected back to back:
Multiple LDEs Back to Back

An experimental setup, in which LEDs are connected in linear fashion using simple numbering system

When the propeller is rotated and the LEDs glow, dark lines can be seen in between the concentric blue circles. If someone wants to display a "solid - filled" blue color, then it is simply not possible due to the opaque boundary between two consecutive LEDs. In this text this phenomenon is termed as formation of "Dark Circles"
Dark Circles
The image below illustrates the same problem with a more complex pattern
Undesired Dark Circles

If a solid-filled color is desired, then its simple not-possible, due to boundary between two LEDs. However close someone may stick two consecutive LEDs but can't put one LED into another!
No Dark Circles Dark Circles
Desired Pattern: Solid FIll   Undesired: Dark Circles
  (Assume 14 visible dark circles)

In order to remove the above problem, the concept of ODD and EVEN LED groups was used. HOW?

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