PROJECTS
●●●●
■ THIS MONTH’S PROJECTS
Auxiliary RC Control Unit . . . . . .32
Weather Projects . . . . . . . . . . . . . 38
The Perceptron Circuit . . . . . . . . 44
■ LEVEL RATING SYSTEM
To find out the level of difficulty
for each of these projects, turn
to our ratings for the answers.
●●●● . . . . Beginner Level
●●●● . . . . Intermediate Level
●●●● . . . . Advanced Level
●●●● . . . . Professional Level
The challenge
seemed simple:
have an assistant
control a camera
or other piece of
equipment on a
remote controlled
model aircraft
while the pilot
concentrates on
flying the model.
AUXILIARY
RC CONTROL UNIT
An obvious solution would be to
use a second transmitter/
receiver system on a different
frequency. At our field, this is not
a viable solution because only a
limited number of units are allowed
to be airborne at the same time.
Most RC systems have a trainer
connection on the transmitter. Two
transmitters are connected via this
umbilical cord. The student’s transmitter provides only the modulating signal to the main transmitter. A
switch on the main transmitter
allows the instructor to connect or
disconnect the trainee. The only
requirement here is that both units
use the same number of channels
and the same type of modulation.
However, it is all or nothing. Either
the instructor controls all the channels or the student has full control.
The primary channels, i.e., the
first four channels are typically
ailerons, elevator, throttle, and rudder. The remaining two or more
channels are used for flaps, landing
■ FIGURE 1. Buddy box connector
rear of transmitter
gear, etc. The solution here is to
replace control of the last two
channels in either a six or eight
channel system with signals from
an auxiliary unit. For the purpose of
this discussion, we will use a six
channel system. The auxiliary control unit achieves this with a simple
but elegant circuit without resorting
to the use of a microprocessor. It
should be noted that this scheme is
limited to systems using pulse
position modulation (PPM).
Tools and Circuit
Board
The unit can be built using
standard tools. It may be wire
wrapped, point-to-point wired, or on
a printed circuit board. I used a preprinted board which worked very
well. The only other tool required is
a dual channel oscilloscope.
Prepare the
Connecting Cable
You will need a six pin male
connector to match with the
connector on the back of the
transmitter. Use a shielded cable
with at least three wires. Pin 1
is + 9. 6 volts, battery negative
connects to the shield of the
connector; pin 2 is the PPM signal
from the transmitter; and pin 3 is
the PPM signal returning to the
transmitter. Note that the power for
the ACU (auxiliary control unit) is
supplied by the transmitter. Figure
1 shows the connector as seen on
the back of the transmitter.
32
January 2006
