■ The schematic illustrates the simplicity of the
BalloonSat Easy. It’s a programmable data logger that
can operate a servo along with a camera. That’s nice,
because a single camera mounted to a servo can take
pictures like three stationary cameras.
The BalloonSat Easy PCB (printed
circuit board) is easier to assemble
if you start with the low lying
components first. Therefore,
assemble the BalloonSat Easy by first
inserting and soldering the three
jumper wires. The most convenient
way to make them are to cut leads of
resistors. Bend them into the proper
sized staple shape before trying to
insert them into the PCB.
Next up are the diode and
resistors. The diode protects the
PICAXE from EMF kickback when the
relay shuts off. I don't suppose there's
much of a kick with this small of a
relay, but I'd hate to take the risk at
100,000 feet. So, think of the diode
as making the BalloonSat Easy just a
little more bullet-proof.
The 22K and 10K resistors in the
upper left are for the programming
header. The 4.7K resistors are
pull-ups for the I2C memory and the
PICAXE-18X reset pin. To prevent
accidents from occurring during the
mission, there's no switch to reset the
PICAXE. The other 10K resistor is the
pull-up for the Commit Header,
which is described later.
Next, install the two IC sockets.
Electrically their orientation is
irrelevant, however, their markings
indicate the proper orientation of the
PICAXE-18X and the I2C memory.
So, orient them as illustrated in the
Install the relay, the 22 µF
capacitor, the 1,000 or 2,200 µF
capacitor (if your BalloonSat Easy will
operate servos), and the voltage
regulator. The relay can't be inserted
backwards, but the other components can. So, watch their orientation
because the BalloonSat Easy won't
work with them installed backwards.
Now that the components have
been soldered to the PCB, it's time to
add the cabling. All the cables are
routed through the strain relief holes
near the edge of the PCB before
they are soldered to the PCB. Drill
the stain relief holes 1.5 mm in
diameter so they are large enough for
#24 AWG wire.
The first two cables are the
battery snap and the camera cable.
These cables remain inside the
BalloonSat airframe and are not
routed to the airframe. A nine volt
battery snap is sufficient for the
BalloonSat Easy in most cases.
However, if the mission requires a lot
of servo work, you'll want to replace
the nine volt battery snap with a six
volt battery pack. A four "AAA"
battery pack works well for this, but
does raise the final weight of the
BalloonSat. In the parts placement
diagram, the positive lead of the
battery cable is colored red and the
negative is colored green. It's best to
terminate the camera cable in some
type of electrical connector. That
way, the camera doesn't dangle
from the end of the cable while the
BalloonSat is under construction. I
like using Dean's Micro Plugs for this
purpose. A bag costs less than $3
and contains two sets of connectors;
enough for the BalloonSat Easy and
The remaining three cables are
the power switch, the LED power
May 2009 81