While the holidays are coming to a close, there’s always time to design festive ornaments driven by cheap microcontrollers, which is what engineer Adam Zeloof did with his Big Ben replica and double-decker bus.
“I guess living in London has really gotten to me, because this year I decided to go a bit crazy with my annual PCB ornaments and design two: a reverse-lit double-decker bus and a tiny Big Ben, complete with E-Paper display because Christmas trees obviously need clocks,” Zeloof noted his Twitter feed.
Zeloof designed Big Ben around an ATmega328P microcontroller, which coordinates a real-time clock, RAM, and an ePaper display. The clock uses an Arduino sketch and requires the Waveshare EPD library and RTClib, while the clock face is a bitmap (stored in memory) and the hands are dynamically drawn with lines and circles.
Meanwhile, Zeloof’s double-decker bus is outfitted with an ATtiny85 that drives 12 Charlieplexed reverse-mounted LEDs. Although only four pins are used on the microcontroller, each LED is still individually addressable. The ornament is also equipped with a push-button for switching between different lighting modes and is powered by a pair of CR2025 batteries that feed a 3.3 V buck converter. Zeloof admits there’s an issue with the bus, stating that it shouldn’t power the PCB when programming, as it will immediately fry the converter. To mitigate the issue, Zeloof cut the VCC trace to the ICSP and connected that pin to the unused pin of the power switch via a bodged wire.