Page 124 - 15 Dangerously Mad Projects for the Evil Genius

Chapter 8 ■ Persistence-of-Vision Display 103

Figure 8-34 Modifying the message

can find this tool on the book’s web site at constructing an image by turning LEDs on and off
www.dangerouslymad.com. as they move past the observer’s field of view.
Figure 8-35 illustrates this point.

Theory
The Software
This project includes some interesting bits of
The Arduino sketch for the Persistence of Vision
theory. There is the psychological persistence-of-
project in shown in Listing 8-1 on the next page.
vision effect, and the software to achieve the
effect, as well as the use of pulse width modulation The first line of the program, or “sketch” as they
(PWM) to control the speed of a motor. are known in the Arduino community, sets the
“period” in microseconds between displaying each
successive column. You can experiment with
POV
changing this value.
This project works for the same reason that movies
We then define a two-dimensional array to
work. If images are presented to the brain faster
represent the Arduino pins used by the LEDs. The
than around 25 frames per second, then we
first dimension is the LED’s row and the second is
interpret the image as moving. In this case, we are
the individual red, green, or blue element within
not presenting a whole image at once, but rather
the LED. So, as we know from the wiring diagram,