A Mercury-Driven Thought Experiment Leads to Mitxela's Cleverly-Built Fluid Simulation Pendant

Mitxela's Tim Alex Jacobs has built a series of artistic wearable pendants adorned with a diagonally-charlieplexed LED matrix — which simulate fluid dynamics as they move around, after a thought experiment involving a mercury-powered fluid simulation simulation.

"[This is] a handcrafted piece of jewellery running a realtime FLIP fluid simulation. The enclosure is gold plated, and the display is protected by a watch glass," Jacobs writes of one of the pendants in question. "I've been looking to implement a realtime fluid simulation that ultimately could create a 3D virtual snowglobe. Progress has been made on that front, but along the way, we came up with the Simsim concept, upon which this pendant is based."

Simsim, unveiled by Jacobs in March last year, served as a thought experiment for another way to build the pendants: a circular grid of LEDs arranged as to be wired to a single power rail and with the ground pin exposed on the rear as pads. Behind the suitably-enclosed PCB is a shot of liquid mercury, which swirls around in a gap at the rear in order to complete the circuit and light up the LEDs — effectively simulating a fluid simulation using real fluid, hence Simsim. "In essence," Jacobs explained at the time, "what we're building is one big mercury tilt switch."

Mercury, however, isn't exactly the friendliest of materials, and keeping it from escaping the device would be a challenge — which is why the real pendants settle for a more traditional simulation, based on Matthias Müller's work on a two-dimensional FLIP simulator. " My fluid simulation is not a direct port," Jacobs says, "but a re-implementation following [Müller's] tutorial."

Inside the housing is an STMicroelectronics STM32L432KC microcontroller, with its Arm Cortex-M4F core overclocked to 100MHz, an Analog Devices ADXL362 accelerometer, and a power system comprised of a Texas Instruments TPS3839 supervisor, a low-power TI TPS7A02 regulator, and a Microchip MCP73832 charge controller linked to a LiR2450 battery charged using a magnetic connector on the pendant's base. The LED matrix, meanwhile, uses a twist on traditional charlieplexing known as "diagonal charlieplexing" — reducing the number of vias required by half and allowing up to 240 LEDs to be driven by just 16 general-purpose input/output (GPIO) pins, of which the pendant uses 216.

"I think I need to invest in yet more equipment, learn more about jewellery making, and ideally, what I really want is to have a decent metal shop at home," Jacobs says of future plans for the project. "That either means moving out of London or trying to come up with something that fits the space. If we want to practice and improve our skills, nothing beats having our own shop that can be accessed whenever and treated however and messy forever."

A detailed write-up is available on Jacobs' website.