28 Silicon chip Australia’s electronics magazine siliconchip.com.au
19111182 Flipdot Display Pixel Elements x 16ÓSC 20 1 9
pieces, as shown in Fig.3.
Carefully break the frame pieces out
of the PCB panel. You may find it easier
to cut one side out of the panel with
side-cutters before separating each ele-
ment along the perforated mouse-bites.
The frame pieces do not need to be
cleaned up to work correctly, although
they can be filed flat along the mouse-
bite edges if you prefer. The PCBs are
made of fibreglass, so any filing should
be done outside with a mask, to avoid
breathing in fibres.
The long, flat edge is visible from the
front of the display when mounted, so
you may wish to colour this black (eg
with a marker or paint) to improve the
contrast of the display. Note that while
our photos show green frames on our
prototype, the final boards (available
from the SILICON CHIP ONLINE SHOP)
will have a black solder mask instead.
The frames sit on the front of the coil
PCB but are soldered at the back, so
you won’t see any solder when looking
at the display later. Line up the edges
of the two PCBs; the frame should sit
at right-angles to the coil PCB. You
will need a fairly large soldering iron
tip and be generous with the solder to
ensure the fillet bridges the gap.
It’s a good idea to solder one of the
tabs at the back and check the position
before soldering a tab at the other end.
You might like to leave just one tab
soldered until the flaps are fitted, as
this will give a small amount of flex
to the frame, allowing the flaps to be
slotted in with less effort.
Fig.6: as with the
frame pieces, the
sixteen pixel flaps
are made from PCB
material and come
joined together. Cut
along the red lines
using a sharp pair
of side cutters, then
separate them at
the ‘mouse bites’.
You can use a file
to gently clean up
the rough edges
if necessary. The
magnets are glued
into the grey-shaded
holes in the middle
of each pixel.If you do this, though, make sure
to come back later and solder at least
one more tab on each frame piece,
once you have confirmed that the unit
works correctly.
The coil PCB is probably the most
delicate part, as the fine copper traces
are near the limit of manufacturing tol-
erances. The traces run quite close to
the edge of the board, and if they are
damaged, they will be next to impos-
sible to repair and the display may not
work correctly. So be careful with it.
On the reverse of the coil PCB, there
are pads for four 2x2 pin SMD male
headers - see Fig.4. These headers are
a similar size overall to their through-
hole equivalent.
It’s a good idea to push the female
header sockets (which will be
soldered to the driver board
later) over the pins on the SMD
headers before soldering them.
This way, if too accidentally ap-
ply too much heat, they should
stay in alignment.
The use of surface mount head-
ers here means that the front of the
display remains unspoiled by sol-
dered joins.
As with any other SMD part, the sim-
plest way to locate the headers correct-
ly is to solder one pin in place, then,after checking that it is in the correct
location, solder the remainder. The
mating holes for the female headers
on the driver PCB are slightly oversize,
to allow for minor inaccuracies in the
placement of the male headers.Driver PCB construction
The driver PCB can be built next.
We recommend fitting the ICs first, as
their placement is not critical. Refer
to Fig.5, the PCB overlay diagram, to
see which parts go where.
IC1 and IC2 are both 74HC595s and
these are fitted at the top of the PCB,
with their pin 1 facing down. IC3-IC6
are L293D types, and these go at the
bottom of the PCB, with their pin 1 to
the left. All six ICs have 16 pins, so
take care that they do not get mixed up.
We recommend soldering them all
directly to the board, rather than using
sockets, for reliability (and because the
pins of IC3-IC6 carry fairly high cur-
rents). You could use sockets for IC1
& IC2 if you really want to.
After confirming that the ICs are
well seated and correctly orientated,
solder all the pins to the PCB, ensur-
ing that you do not put too much heat
into the IC. The ground pins on IC3-
IC6 (the four pins closest to the centre)
sit on a large copper area to provide
some heatsinking, so these pins may
require extra heat to ensure a good
solder joint.
Next, mount the capacitors. Both
are the polarised electrolytic type,
so observe the polarity marks on the
PCB. The longer leads go into the
pads marked with a “+” sign, while
the striped side of the can is nega-
tive. The smaller 10μF capacitor sitsThe pixel flaps are a simple press-fit into
the holes. Ensure that the colours are
aligned as shown, slot one tab in the lower
hole and then rotate the flap to snap the
other tab into the upper hole.