22 Silicon chip Australia’s electronics magazine siliconchip.com.au
If you want a dot matrix display which has digits/letters over 90mm
high, is visible under a wide range of lighting conditions and uses no
power except when the display is changing, then our new and very cool
FLIP-DOT display is for you. Seeing (and hearing) a flip dot display is
quite something, so it makes a great conversation starter too!
BUILD YOUR OWN E-X-P-A-N-D-A-B-L-E
Y
ou’ve probably seen the large
yellow dot displays on the
front of many Australian bus-
es, trains, etc or perhaps in airports.
They’re highly visible in bright sun-
light or under cloudy skies, and they’re
usually illuminated at night too.
Contrary to what you might believe,
they’re generally not electronic signs
as such: they’re actually electrome-
chanical flip-dot displays.
They’re made from panels that are
yellow on one side and black on the
other. They rotate to change state, ac-
companied by a pleasing “clack-clack-
clack” sound.
Well, now you can build your very
own home flip-dot display! It’s easy
to build, uses just a handful of read-
ily available parts and is controlled
by an Arduino or MicroMite micro-
controller.
So you can make it read just about
anything you want. If you use a micro
with a WiFI adaptor, you can even get
it to download and display data from
the internet, such as the temperature
forecast or sports scores.
So-called flip-dot or flip-disc dis-
plays have been around for over 50
years and are still commonly used in
countless applications.
Their simplicity and reliability have
stood the test of time, and now, you
can build your own.
For those not familiar with this type
of display, each disc or
flap which forms a pixel
in the dot-matrix display
also contains a small permanent mag-
net. An electromagnet can flip this
magnet and thus the disc, to control
which colour is visible from the out-
side. The polarity of the coil drive cur-
rent determines which side of the disc
appears. When power is removed, the
display remains in its last state.
These displays are designed for thediscs to remain stationary until com-
manded to move. Our version has been
simplified to make it as easy as pos-
sible to build, but it will still make a
practical stationary display, and one
which can be seen quite well in vari-
ous lighting conditions and across a
large room.
Many commercial flip-dot displays
use numerous small coils wound onto
tiny armatures – see the photo of one
on page 24.How our flip-dot display works
To simplify our display and make
it substantially cheaper and easier to
build, we have formed coils using PCB
tracks instead. One PCB contains fif-
teen such coils on both layers – enough
to produce a single character display
by itself.
Each board consists of a matrix of
fifteen pixels, arranged three wide by
five high. This is just enough to dis-
play a capital letter, number or sym-
bol. Each pixel consists of a piece of
fibreglass that’s black on one side and
white on the other, with an embedded
rare-earth magnet.
These sit over the PCB-track coils
and are attached to that board in such
a way that they can rotate through 180°
on a pair of simple hinges, allowing
either side of the black/white panel
to be made visible.
The PCB underneath is also white
on one side and black on
the other, so that when
the panel with the mag-One complete unit – here displaying
the letter “S” – sits upright of its own
accord. We have fitted a small length
of female header strip to CON1 and
CON3 to allow connections to be
made with jumper wires. See video:
siliconchip.com.au/Videos/Flip-dot