Page 201 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

180 Bu il d Y o ur O w n Q u a d c o p t e r

Figure 7.18 Early version of an Elev-8 LED-lighting controller.

LED strips flash in a variety of patterns that just kept repeating, in a way that reminded folks
who saw it of the Close Encounters of the Third Kind movie without the music.
The more I thought about it, the more I wanted to be able to send a signal to the
quadcopter to dynamically change the lighting. One thought was to flash just the LEDs
attached to the forward booms so that I could easily see in which direction the quadcopter
was moving, especially as daylight faded. I also wanted to stop the flashing entirely in order
to conserve battery energy. These ideas would lead to the following requirements:

• Forward boom LEDs flashing
• All LEDs flashing
• No LEDs flashing
These requirements meant that I needed an unused three-state control switch. By
serendipity, the switch happened to be available on the DX-8 in the form of the Aux-1, or
Flaps, control switch. This light control is an ideal use of the three-position switch because
the Elev-8 does not and will never require flaps.
I tested the switch shown in Figure 7.19 and determined that it generated the following
pulse widths for the three switch positions, as shown in Table 7.2.
The LED light strips cannot be run directly from the BOE because the current draw is too
high. Therefore, I created four transistor driver circuits that control the four strips based on

Switch Position Pulse Width (ms)
0 1.898
1 1.505
2 1.111

Table 7.2 Aux-1 (Flaps) Pulse Width versus Switch Position