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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