An ultrathin business card uses a fluid simulation to make hardware feel alive

# An ultrathin business card uses a fluid simulation to make hardware feel alive

The GitHub project combines PCB design, firmware and a simulation crate to turn a card into a tiny moving display.

The flip-card project on GitHub is the sort of hardware experiment that makes embedded engineering look like magic. According to the repository, the device is an ultrathin business card that runs a fluid simulation, with the board design, firmware and simulation logic all published in one place. That combination makes it more than a novelty object. It is a small, carefully documented demonstration of what happens when software, electronics and industrial design are treated as a single system.

The project description says the PCB design files live in a dedicated folder, while the fluid simulation itself sits in a standalone crate. It also points to a WASM simulator used to debug issues in the simulation before deployment to the actual hardware. That matters because the card is not just a pretty object on a desk. It is a hardware platform with enough complexity to require proper simulation, testing and iteration before the fluid motion behaves the way the maker wants.

The inspiration chain is also interesting. The repository credits mitxela’s fluid simulation pendant project as part of its lineage and says the simulation logic is based on work by Matthias Müller and demonstrations from Ten Minute Physics. That is a reminder that a lot of hardware creativity is cumulative. One project seeds another, and the result is often less about inventing a brand-new idea than about packaging an old one in a more surprising physical form.

The card also had to solve the ordinary problems that make hardware difficult. The repo notes a rechargeable battery design, a USB-C board-edge port borrowed from another project and support for flashing instructions in a dedicated firmware subfolder. Those details matter because the interesting part of a project like this is not only the visual effect but the accumulation of practical choices that make the effect feasible in a small footprint.

What gives the project broad appeal is that it turns a business card, normally a flat object with limited use, into something that feels responsive. A fluid simulation is a clever fit for a tiny display because it creates motion that looks rich even when the hardware is small. That is exactly the sort of constraint-aware design choice that gives maker projects staying power: the feature is visually rich, but it also fits the object’s form.

The GitHub write-up suggests the author built this partly for the challenge of it and partly because the result would be memorable. That blend of technical ambition and playful aesthetics is the reason projects like this travel well online. They show that embedded systems do not have to be purely utilitarian. They can be expressive objects, too, especially when the maker is willing to write custom firmware and arrange the whole stack around a single effect.

In the end, the project says as much about modern hardware culture as it does about fluid dynamics. The card is thin, but the work behind it is not. It involves board design, simulation, firmware and enough debugging infrastructure to make the final object feel polished rather than improvised. That is the real story: a tiny device that looks whimsical on the outside and highly disciplined underneath.