YOUR OFFICIAL RASPBERRY PI MAGAZINE

THE STORY TRAIN
Tutorial
EMBEDDING THE SENSOR SWITCHES
>STEP-01
Rough out the recess
Drill a sequence of holes close to an
open end of a length of track. Choose
a drill size to match the diameter of
your reed switch. Drill a blind hole to
the depth of the reed switch’s diameter.
The track layout
The wooden train track can be laid out in many
different ways, although there are only two basic
topologies: a loop or single-ended. We favour the
loop because it’s obvious what you need to do to
drive the story on. At the end of each page of the
story, you just drive the train around the track to
move on to the next page. At least two switches are
required: one at point A, and the other at point B.
However, this is not critical at all, as long as they are
separated so that only one switch can be triggered at
a time. You could use more switches at other parts
of the track to trigger extra sound effects if you like.
We found that someone had written a program to
generate all the possible track layouts for the basic
Lillibo set; the code is online here:
magpi.cc/1NM4vUh.
The software
The idea is that when the train pulls into the station,
a page is produced and a sound sample is played. This
page can be text, just pictures, or a mixture of both.
When the page has been read and the sound sample
played, the software looks for the other switch being
triggered. When it sees that, a second sound effect
is played and the program then looks for the station
switch to be triggered before producing the next page.
In this way, there’s no problem with contact bounce
on the switches, nor from multiple triggering due to
the carriage’s coupling magnets.
>STEP-02
Finish the recess
Fit a router bit to the drill and join up the blind
holes. Make a smooth recess so that the reed
switch can sit flush with the surface of the rail.
The media
The electronic book consists of a number of pages,
each comprising a JPEG image file and a WAV sound
file. These have to be prepared in advance, and
these pages are what the Story Train is presenting
as the story unfolds. Older children can write their
own stories and draw accompanying pictures;
youngsters or a teacher can write a story or borrow
one from a book. The image files can be produced in
any package; for keeping it all on the Pi, however, the
Inkscape application is hard to beat, especially on the
faster Model 2 Pi.
raspberrypi.org/magpi January 2016 55