the PicoBoard, distributed by Sparkfun
( www.sparkfun.com/products/10311).
It costs less than $50 and can be used
with the Scratch programming language, making it useful for novices. The
PicoBoard has a low threshold and a
high ceiling. We have used it with students in the upper elementary grades,
but we have also used it with high
school students who have incorporated
it into sophisticated projects.
The PicoBoard has built-in sound
and light sensors that students can use
immediately, but it also has four additional inputs for other types of sensors. Here is how to use the PicoBoard
and Scratch to reproduce a visual telegraph for an introductory project.
Designing a Visual Telegraph
The early telegraph, invented by Samuel
Morse, produced a paper copy marked
with raised dots and dashes. This visual
telegraph was subsequently supplanted
by an auditory telegraph, in which operators used the sound of the telegraph key
to translate the message. The teletype,
which eventually replaced the telegraph
key, once again used paper tape to retransmit relayed messages.
You can emulate all three variants
of the telegraph with a PicoBoard and
sensors. In the process, students learn
foundational concepts that prepare
them to make use of other types of
sensors in science projects.
Students could use two pieces of
foil to create a switch for a circuit
that connects a light bulb and a battery. Closing the switch will turn on
the bulb to verify that the circuit is
working. If they connect the switch
to a PicoBoard input instead, the
PicoBoard can monitor the output.
Each of four external inputs measures
resistance. In this instance, when the
switch is closed, it generates a value of
100. When the switch is open, a value
of zero appears. Students can use a
Scratch script to display these numeric
values. You can download the script
for this Scratch program and other
resources referenced in this column
at the Make To Learn website (www.
MakeToLearn.org/telegraph).
Once students display the numeric
values of the switch (open and closed)
using the PicoBoard, they can plot the
values on a computer screen.
Imagine a pen that travels just
above the surface of the screen. This
electronic pen lowers to draw a line
when students close the switch. This
displays a series of dashes and dots on
the screen, depending on the length of
time that students depress the switch.
The result is a visual representation of
the Morse code they have generated.
3D-Printed Telegraph
Many schools are acquiring 3D printers
as the cost becomes increasingly affordable. We have provided a downloadable
file that classes can use to print a working telegraph key instead of a foil switch.
If you don’t have a PicoBoard, you
can adapt the script to monitor a key
on the keyboard. For example, this
could allow the spacebar on the keyboard to serve as a substitute for a
telegraph key. We have also provided
this variant of the script on the Make
To Learn website.
This exercise can familiarize stu-
dents with the PicoBoard and with
creating and interpreting visual dis-
plays associated with digitized analog
signals. The signal produced in this
instance is binary: It is either on or off.
This also serves as an introduction for
explorations with sensors whose values
vary across a range. For example, the
class could use a thermistor to monitor temperatures or a motion sensor
to monitor the movement of an object.
These activities all involve monitoring
an external signal by A/D conversion.
Controlling External Devices
Reversing this process through the
use of a digital-to-analog converter
(DAC) allows a computer to control
objects in the physical world. A computer can control motors, solenoids,
and other actuators based on the input
it receives. For example, in a model
house, a heater (simulated by a light
bulb) could be turned on when the
temperature in the house, monitored
by a temperature sensor, drops below
a predetermined point.
The Next Generation Science Standards call for integration of science
and engineering. The rationale is that
students can better understand concepts when they learn them in context.
The type of activities we have described help students understand the
principles underlying technology in
their homes as they learn about related
science and engineering concepts.
Glen Bull is co-director of
the Center for Technology
and Teacher Education in
the Curry School of Education
at the University of Virginia,
USA. He may be reached at
gbull@virginia.edu.
Jonathan Cohen is a graduate
fellow in the Center for Technology and Teacher Education. He can be reached at
JonathanCohen@virginia.edu.
