siliconchip.com.au Australia’s electronics magazine April 2019 23
Features:
- 15-pixel display per board (three pixels wide, five pixels high)
- Each board can display a single letter, number or symbol
- Display boards can be daisy-chained for multi-character displays
- Customisable colours (BYO paint!)
- 5V/3.3V 4-wire serial interface
- 12V power supply required – 1.5A or higher (see text)
- Each pixel controlled individually
- Stackable for multi-row displays
net flips, the whole area changes from
black to white or vice versa.
All that the driver board needs to do
to cause it to flip is to energise the coil
underneath with the correct polarity.
This will repel the magnet initially,
causing the panel to swing through 90°
until it is at right angles to the panel
below. The magnet will then be at-
tracted to the coil and continue mov-
ing due to inertia, until it is laying flat
on the panel below but with the op-
posite orientation.
The pixel size (19mm wide and
17mm tall) is a compromise between
the magnetic strength of the coil and
the weight of the moving elements.
Each coil has around 60 turns and
measures just over 1.5m in track
length, but is packed into an area less
than four square centimetres. This is
about the limit of what is possible with
a two-layer board.
The magnets are 3mm x 1.5mm rare
earth magnets glued into a hole on the
flap PCB. It is important that the mag-
nets all face the same way relative to
the colours. This ensures that the flaps
are interchangeable and consistently
display the same colour.The pixel flaps and the brackets
holding the flaps to the panel are small
PCBs too. A completed unit including
the driver PCB will consist of 23 sepa-
rate PCB pieces. The bracket PCBs are
soldered to the main coil PCB, and
the flaps are slotted in place, pivoting
around their end tabs.
PCBs are a cheap, convenient way to
achieve the correct mechanical dimen-
sions required of multiple identical
parts. By using PCBs with a black sol-
der mask and white silkscreen print-
ing, we can use the silkscreen layer to
create pixels with very high contrast