TINY LED
ICICLE
by Tim Blythman
This miniature ‘icicle’ is perfect to match the look of a winter Christmas,
despite the summer in Australia. This Icicle Ornament also has two power
connections, making it easy to power a series of them on a single supply.
I
cicle-style Christmas lights are very
popular. With vertical strings of
lights that are often arranged in
groups, they evoke the appearance of
icicles hanging from eaves.
The Tiny Xmas Ornaments from the
November 2020 issue (siliconchip.au/
Article/14636) were a great hit, and we
recently thought that an Icicle shape
would be a great addition. So we’ve
added an Icicle design to the cohort of
tiny Ornaments you can create.
The Icicle has a handy feature
shared with the Reindeer Ornament
published previously in that it has
two power connections (as well as an
onboard cell holder). That makes it
easy to create a long chain and power
it from a single power supply, such as
a 2×AA battery holder.
To keep things simple, we’ve laid
out the LEDs in a simple top-to-bottom
order, the same as the existing Stocking Ornament. The firmware for the
Stocking simply flashes the LEDs in
order from top to bottom. The Icicle
therefore reuses the existing code/HEX
file from the Stocking. The resulting
downward movement evokes water
dripping from the Icicle.
The circuit and parts list are thus
the same as the Reindeer Ornament
(except for a different PCB), and the
firmware is the same as that for the
Stocking. Easy!
We tried a few different LED colours
on our prototypes, and an assortment
of colours looks quite good, but using
all blue or white LEDs (or a mix) creates a striking effect.
For more background, refer to the
article from November 2020 or even
the original Tiny Tree from November
2019 (siliconchip.au/Article/12086).
The 2019 article explains how we
Parts List – Tiny LED Icicle
Wires go out one side of
the Icicle PCB and into
the other side of the next.
Both are in parallel, so the
battery holder can feed in at
either end of the chain.
28
Silicon Chip
Australia's electronics magazine
1 white double-sided PCB coded 16111192,
98.5 × 98.5mm (41 × 127mm upright)
1 PIC12F1571-I/SN (/1572-I/SN) or
PIC16F15213-I/SN (/15214-I/SN) 8-bit
microcontroller, SOIC-8, programmed
with the appropriate version of
16111194.HEX (IC1)
12 SMD LEDs, M3216/1206 or SMA size,
any colour (blue, cyan and/or white
recommended)
1 SMD coin cell holder [BAT-HLD-001]
1 CR2032 or similar 3V coin cell, or 3V
battery pack
1 10kΩ SMD resistor, M3216/1206 size
4 100Ω SMD resistors, M3216/1206 size
1 5-pin right-angle header (CON1; optional;
for power/programming)
1 2-pin right-angle header (CON2; power)
1 length of light-duty figure-8 wire (if daisy
chaining boards; eg, from ribbon cable)
1 M3 x 6mm Nylon screw
2 M3 nuts
SC5579 Kit ($15)
Choose from a variety of ornaments,
each one is supplied with the parts above
(except the coin cell, CON2 & figure-8 wire)
and assorted LEDs to match.
siliconchip.com.au
control 12 LEDs from a tiny 8-pin
microcontroller.
We will be adding the Icicle to the
list of Ornament kits available. You
can order kits from siliconchip.au/
Shop/20/5579 – just be sure to select
the correct colour and type of PCB
(white only for the Icicle). Unlike the
other Ornament kits, which come with
12 each green, red and white LEDs,
the Icicle kits will come with 12 each
blue, cyan and white LEDs.
Construction is simple enough; refer
to the older articles if you need more
details. The main thing to check is
that all the LED cathodes align with
the markings on the PCB; they should
all face the same way (to the left with
it upright). The PIC is the only other
polarised part, although you should
be careful installing the cell holder, to
be sure that it will allow the battery
to be inserted; it only has an opening
on one side.
You don’t need to fit the cell holder
if you are using a battery holder to
power multiple Icicles but mind the
polarity marked on the reverse of the
PCB. We’ve used red and black wires
to make it clear which is which, but
you can use other colours as long as
you don’t get them mixed up.
Programming is not necessary if you
have bought our kit, but if you have
a blank PIC12F1571 or PIC12F1572
microcontroller, you can use a PICkit
3, PICkit 4 or Snap. The PICkit 3 is
not compatible with the newer parts
like the PIC16F15213 or PIC16F15214
(which are generally more available),
so you’ll have to use a PICkit 4 or Snap
for these parts.
The Icicle should start flashing
when programming is complete,
although you might find some LEDs
stuck on if the programmer is still connected. One pin is shared between the
programmer and the LEDs.
If you are building a chain of Icicles, test each individually before
joining them together. They are all
programmed to flash at the same rate,
but minor variations in processor frequency mean they will quickly fall
out of sync.
Finally, secure the coin cell with a
Nylon M3 × 6mm screw and two nuts
against each other to lock them. SC
CAUTION: Coin Cells
Coin cells should be kept well away from
children who may ingest them. Make sure
the cell is secured firmly in place.
siliconchip.com.au
Fig.1: 12 LEDs are driven with just four microcontroller I/O pins using a scheme
called Charlieplexing, explained in the November 2019 article. The Icicle is
similar to the Reindeer as it has an extra connector for daisy-chaining power.
Figs.2 & 3: there are parts on both sides of the PCB, but the front is clear of
markings for a good presentation. Take care that the LEDs line up with their
cathode markings, which are just visible. The LED cathodes all face to the left
(when the Icicle is upright); there is a cathode mark on the PCB silkscreen. On
the reverse, only microcontroller IC1 is polarised.
Australia's electronics magazine
November 2022 29
