combined. The MP3 player is at mdfly.com. Shipping is
not free, but the module is under $10. The MP3 module
uses one processor output in serial mode and the four-channel remote uses four processor inputs. That leaves
enough I/O for four servos and five digital FET-driven
motors or lights. The modules are shown in Figure 2.
An 11.1 volt lithium-ion battery is used for the system.
These batteries can be found on the Web or in local
hobby stores. The board has separate five volt and six
volt regulators. Thus, the six volt servos won’t
accidently reset the five volt processor when drawing
higher currents. Three diodes are included to prevent
accidental voltage reversal, and to drop some voltage
for the 9V relay.
Safety note: Please remove the lithium-ion battery
from the prop board to be recharged in a charger
designed for these batteries! No circuit is provided on
the PCB to recharge the battery.
Prop Board Construction
Use your favorite method to etch the single-sided
PCB. I used toner transfer film and ferric chloride. Just
about everything on this board is polarity sensitive, so
a top component placement diagram is included in
Figures 3 and 4.
Monster Book Construction
Drill .130 holes directly through the center of the
2” wood balls, or at least make sure the balls rotate easily
on the 1/8” steel rod. Use a small wood dowel to hold the
ball and rotate by hand while spray-can painting with gloss
white enamel. Let it dry overnight (Figure 5). The next day,
paint the irises on the eyeballs and let this dry. If you use
plastic irises, then drill the 24 mm (I used a 1” Forstner bit)
inset about 1/8” deep. Follow up with a 1/4” bit to accept
the stud of the iris. Glue the iris in with epoxy. Here’s a
54 SERVO 10.2014
MP3 player, and
three watt amplifier
FIGURE 1. Schematic.
A full size file is available at the article link.