Almost every night I light a candle before going to bed as part of my nighttime routine, so I have heaps of leftover glass jars that seem too nice to throw away. Last weekend my girlfriend and I had the idea to turn one into a nice-looking enclosure for an interactive LED light project.

The first step was cleaning out the old wax and wick.

Next, we made a display that exactly fits the unique shape of the jar. We bought a strip of individually addressable LEDs, cut it into shorter sections, and wired them together into a flexible circular matrix.

As well as adding a rechargeable LiPo battery, we fitted a piezoelectric buzzer into the top of the lid to use as an impact touch sensor. We chose this approach, rather than something like a capacitive touch sensor, because I already had the part, it uses less power, and it could also function as a noise-making device if we choose to add that capability in the future. Tapping the top of the jar toggles the light animations on and off, while double-tapping cycles through the animations.

Finally, we wrapped everything up by writing and flashing the Arduino firmware with a variety of animations. The project is driven by an Adafruit Feather nRF52840 Sense board that I had lying around. It has a 64MHz ARM Cortex-M4F, Bluetooth Low Energy, built-in LiPo charging, and plenty of GPIO, so it is more than capable for the job, with room for additional functionality in the future.

By the end of the weekend, we had turned an empty candle jar into a self-contained LED display with a custom-shaped matrix, battery power, and touch input lid. It’s a very sleek decorative piece, but in the future I would like to make it even smarter, perhaps as a little desktop pet or handy assistant. The sensors on the Feather leave plenty of room for that: motion, gesture, ambient readings, sound response, BLE control, and more expressive animation states.

Check out the code at jar-pet repository.