Back to Concepts

Simsim Pendant

5 Mar 2024
Progress: Concept

It may come as no surprise that one of the projects I'm working on lately is attempting to create a realtime fluid simulation on embedded hardware. There are many applications, from volumetric virtual candles to interesting jewellery and trinkets.

Running a mixed liquid/air simulation is somewhat more complex than a fire simulation, but there's an irrefutable appeal to having a physical item in your hand, displaying a virtual glowing liquid, that sloshes around as you tilt the contraption. Stay tuned for that.

But while discussing methods of chasing this goal, the concept of "faking it" arose – that is, to simulate the simulation, using a real liquid.

Render of PCB with LEDs

Consider a grid of LEDs arranged on a PCB. Instead of a matrix, all the LEDs are wired up to a single power rail. The other connection for each LED is on the underside of the PCB. For each pad, if it's shorted to ground, the LED above it will light up.

Render of underside of PCB with LEDs

We then mount this PCB a small distance away from a glass panel, seal the edges, and partially fill the gap with mercury.

Mercury on the back of the PCB

In essence, what we're building is one big mercury tilt switch.

Render of glass, mercury and PCB stackup

The liquid metal forms the other power connection, and so as it moves around in the sealed chamber, the LEDs above it would light up accordingly.

Mercury, glass and PCB pressed together

It doesn't have to be mercury, of course, there are other alloys available which are less toxic. A mixture of gallium, indium and tin is liquid at room temperature. Depending on the exact ratio, different melting points are achievable. I quite like the idea of a pendant filled with liquid metal that only comes "alive" while it's being worn: the heat of your body keeps it liquid. When you take it off, the liquid freezes and the magic disappears.

Front of device with gold surround

From the front, the device would appear to be running a fluid simulation. From the rear, the truth of liquid metal becomes clear.

Stackup with gold surround

We are presenting a digital render of the device, which makes this a fluid simulation simulation simulation.

LEDs illuminated

LEDs illuminated

Gosh this would be fun to play with.

LEDs illuminated

Rear of device while illuminated

All right – sold – maybe I will build it at some point.