NEAR SPACE
developing this system, but have
recently discovered it is used with
other PCBs.
Both Minis use a nine-volt
battery snap, so pass the stripped
ends of the snap through their strain
relief holes and then solder the end
of each wire to the PCB. Just watch
the polarity of the battery snap when
you solder it (the diagram of parts
placement is color coded, so you
can't mix the wires).
The three remaining wire pairs
in the BalloonSat Minis are for the
Power Indicator LED, On/Off Switch,
and the Commit Pin. Since
BalloonSats are usually small in size,
the cables can be kept short. Cutting
the wires six to eight inches long
ought to be good enough. Strip one
end of each wire, pass it through its
appropriate strain hole, and then
solder it to the PCB. I like to color
code my wires for the LED so it is
easy to identify the correct ones
when it comes time to solder the
LED to the wires.
After soldering the six wires to
the PCB, strip their free ends in
preparation for the LED, sub-mini toggle switch, and 1/8 inch phono jack
receptacle. The LED cable is stripped
back 1/2 inch, twisted tight, and well
tinned. Slide thin heat shrink over the
tinned leads once the solder has
cooled and push them close to the
PCB (or else they could prematurely
shrink when you attach the LED). Cut
back the leads of the LED to 1/2 inch
and tin them. Double-check your
polarity, then place the proper LED
lead flush against the first wire. Heat
the LED lead and the wire with a well
tinned soldering iron and the two will
fuse together. Repeat this for the
second lead. Then, slide the heat
shrink over the soldered connection
and shrink it. The connection will be
plenty strong.
The solder tabs of the toggle
switch and phono jack have holes to
pass the wires through. So, strip an
adequate length of insulation from
the four remaining wires (one inch of
■ A completed panel for the
power switch, indicator LED,
and commit receptacle. Notice
that the commit pin is made
from a 1/8 inch phono jack.
insulation is about right). The
heat shrink for the toggle
switch and phono jack receptacle is larger than it is for the
LED and needs to be test-fitted before you cut it. As
you did for the LED, slide the
cut heat shrink up against the
PCB so it cannot prematurely
shrink. Now pass two-thirds
of a bare wire through one hole in a
solder tab in the phono jack receptacle and twist the wire tight around
itself. Solder the twisted wire with
just enough solder to lightly coat the
twisted wires. Verify no blob of
solder is bridging the gap between
the solder tabs, then slide the heat
shrink over the connection and heat.
Repeat this for the remaining three
wires. The BalloonSat Mini 2 has an
additional cable for the camera. I
strongly recommend the end of this
cable be terminated in a connector
rather than permanently attached
to a camera. If the camera is
permanently attached, then eventually
the cable between the Mini 2 and
camera will break from the weight of
the camera. I use either a small
Dean's connector or a male header.
The termination that you use will
depend on how you modify your
camera. However, I recommend
picking a single type of connector
and sticking with it.
TESTING AND PAINTING
At this point, you have a
complete BalloonSat Mini. However,
before snapping in the PICAXE-08M,
take a moment to check your soldering for unintentional shorts (do we
ever have intentional shorts?). Make
sure solder did not overflow its pad
and that no cut leads are sticking to
the bottom of the PCB. After a visual
check, get out a multimeter and
check for continuity between power
and ground in the battery snap. Be
sure to check with the power switch
both turned off and on. If no short is
detected, then attach the nine volt
battery to the Mini and flip the
power switch. You will see the LED
light up, indicating power. Now, set
your multimeter to measure voltage.
Between pins 1 and 8 of the
PICAXE you should measure five
volts — give or take 5% — or between
4. 75 and 5. 25 volts. Then, check the
voltage of the I/O ports. To do this,
stick cut resistor leads into a +5V and
a ground hole of the receptacle to
make it accessible to the multimeter.
Again, you should measure within
5% of five volts in the receptacle. Of
course, if the battery catches fire and
sparks fly out of the PCB, disconnect
power and look for a short.
Turn off the power before you
snap the PICAXE-08M into its socket.
A PICAXE-08 will work in the Mini,
■ A side view of the BalloonSat
airframe sandwiched between the
instrument panel (seen with a switch
and LED) and the reinforcement ring.
March 2009 79