Everyone knows the adage “what goes up, must come
down,” which certainly applies to high altitude ballooning
here in New England. With the Atlantic on our doorstep,
mountains to the north, and densely populated cities with
tall trees in between, we needed a way to terminate near
space balloon flights so that the payload came down in a
place where it could be safely recovered. (Oh, I forgot to
mention airports and highways.)
Our goal for the onboard electronics was to develop
the hardware and code necessary to support acquisition
and recording of data from multiple sensors, and
autonomously terminate a flight by separating the balloon
from the payload.
The Microcontroller
Board
The flight controller consists of two stacked boards
connected by pin headers. We call the bottom board the
microcontroller board and the upper board the sensor
board. The microcontroller board consists of the
microcontroller and its supporting components.
Teaching students to learn about electronics
components, how to solder, and how to use tools was a
priority of this project. With that objective in mind, we
chose the Propeller Platform Thru-Hole kit (PPTH) for the
microcontroller board (Figure 2). Designed by Brian Riley
at wulfden.org, the PPTH is the third generation of the
Propeller Platform first designed by Jon Williams (see
“Stamp Applications” in N&V, May 2009).
The board uses all through-hole components and has
a lot of open space, making it easy for a beginner to stuff.
Another advantage is its use of the 40-pin DIP Propeller
chip (by Parallax) which is easily replaced if damaged
during assembly or during flight. This was important,
given that the boards were built by electronics beginners
overly wielding hot bargain-priced soldering irons.
The Propeller was an easy choice with its multi-core
processor, our familiarity with the product, and the easy-to-learn Spin language.
Stuffing this board is easy. The parts arrived in a
nicely packaged kit. The Wulfden website includes clear
step-by-step build instructions and clear pictures. After
receiving some soldering instruction and practice,
students were able to build nearly flawless boards using
those directions.
The board comes with electrolytic capacitors used to
stabilize the voltage on the input and output sides of the
voltage regulators. We replaced these with tantalum
capacitors on the advice of a satellite design engineer at
the University of New Hampshire. Apparently,
electrolytics can off-gas, dry out, and fail in the extreme
low pressure of near space.
We don’t like the standard coax power jack because
it can be jarred loose during flight. Instead, we use a 22
gauge cable soldered to the positive and negative pads.
Be sure to provide some kind of strain relief at
the board. We terminate the other end with a
reliable power connector such as a JST-RCY.
Students inspect each other’s work after the
stuffing is done. This encourages collaboration,
fosters pride in workmanship, and inspires
quality.
Students go through a NASA style checklist
in which they check voltages at critical pins
before plugging in the Propeller 40-pin DIP. Next,
they ran a test program to check the function of
each pin as an input and then an output. When
they are all done, they know the boards are
good.
We cleaned the finished board and then
applied conformal coating on the solder side to
reduce the chance of shorts caused by
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June 2017 29
■ FIGURE 2. The microcontroller board;Wulfden’s
“Propeller Platform Thru-Hole” kit.
Project SMART
Project SMART is a month long summer program for talented
incoming junior and senior high school students (visit
http://projectsmartspacescience.sr.unh.edu).
The space science component, run by the University of New
Hampshire Institute for the Study of Earth Oceans and Space
(UNH-EOS) under the guidance of Dr. Charles Smith, gives
students the opportunity to work with faculty on authentic
research projects, attend faculty lectures, learn more about
physics, and get their hands busy building a near space ballooning
airframe and sensors. UNH-EOS also supports science club
activities at three area high schools (Coe Brown Northwood
Academy, Timberlane Regional High School, and Londonderry
High School). Students and instructors at all three schools work on
many projects, including design and building of an airframe, flight
path prediction and tracking, radio communications, sensors, and
design and building of the flight controller.
