Ultrathin business card runs a fluid simulation (opens in new tab)

* less joy of doing hard things

Have you tried to fabricate such a box? I wouldn't be so sure.

It also solves a fluid mechanics problem much faster and more accurately than de digital one!

I love good finger toys at my desk to keep my ADD busy while I'm working. They need to be:

- Light: If they make a clanking noise every 5 seconds when you pick them up and put them down its just distracting.

- Plastic: There are other materials that work, but in general metals and fabrics react too strongly with your fingers over time, whereas plastic can be easily cleaned.

Having a little water window isn't a problem, but the water is also not as directly cool looking. Usually in the '90s you'd get those mixed color oil/water toys where the colors would make them stand out more, but shaking them would mix the substances causing them to lose function.

As such the electronic version is quite durable in comparison.

Disadvantages:

  * excessively fast fluid motion at card scale

Starting point: Ocean waves in a bottle

https://www.youtube.com/watch?v=W4jbx5WLhy4

things you get away with when you remove one level of simulation...

* no rust

Maybe you wouldn’t give em to just anybody, but anybody who gets one is guaranteed to remember you!

I’d probably even keep it in my desk to play with. After a few weeks I’d accidentally have this guy’s email/linkedin memorized for eternity

I'd include a sad tomagotchi that after a week or so guilt tripped you into giving it back, its heart broken, missing its original owner.

> but probably a bit too expensive to just hand out.

These are generally done as portfolio projects. It’s driving a lot of traffic to the website.

Producing a small number to hand out to potential freelance clients or job prospects is also common.

I half expected this to have a button/mode to show custom QR codes...

How much does it cost? The guest passes for hacker conferences are full-on computers these days, if this is in the same price bracket it would be a great idea for those.

I wouldn't even necessarily give one to anybody. If you're looking for a job just point to this block post in your resume/site and that's equally impressive.

If you ask for it to be handed back, it's not a business card. It's a toy.

Just put a QR code on the front that transmits a vCard. Or a way to make the LEDs on the back display a QR code. Then you can still show people your digital business card, even let them hold it and play with it, but it's still obvious the idea is for them to scan the QR code and hand it back.

You don't hand out business cards to everyone, only to those who deserve one.

Exactly my thought. Just make it a desk toy.

Wow what a cool retro fluid simulation game!

Oxygen Not Included simulates a whole bunch of different kinds of fluids and gasses, and has a sandbox mode and debug tools.

I love using it as a kidpix-like painting tool, just to see how all the different materials interact.

https://youtu.be/U0MevBWyfS8?t=295

Is there a Digital Disco Ball?

That was very clearly mentioned and linked in the article, too.

+1 for mitxela, dude never ceases to amaze

The circle works much better for the fluid simulation.

Wow that's a nice design.

£1200 for one though.. oof.

I was thinking of throwing in a game like Tetris with just accelerometer controls. That'll be after I find a job though. Numbers were actually the first things I displayed, I actually still have all the code to display them still sitting unused.

Text has been less of a success. Having the letters be easily legible takes more space than I would have thought, and the small pixel fonts don't look great with the big spacing between the LEDs. Maybe some scrolling text would look good, but I haven't focused on it too much. I tried getting a QR code displayed, but it didn't want to scan.

For buttons, I'm kind of married to the idea of no buttons. The accelerometer does recognize clicks and double clicks in different directions, so that might be useful for something.

I encourage anyone who wants to fork/contribute/post issues on this to do so and I'll try to be a good maintainer.

A few business card typography tips off the top of my head:

— White on black (inverse) is less legible, so all else equal compared with black on white the font should be bolder and/or bigger for equivalent readability. (Using caps or small caps is also OK in display text like titles, if it reads easier.)

— Legibility is also impaired by visual noise around the text (it’s not a single color but there is some pattern, for example). Compensate for that, too.

— Unless you really know what you are doing, stick to one font. You can use bolder/lighter variants of the same font.

— Never compress fonts vertically or horizontally. Instead, pick a different font. Many fonts have condensed/compressed alternatives, or there is also Impact if you want it.

— Use white space. Padding lets it breathe.

— Use typographic features. Em dashes (separate them by thin spaces), bullets.

> Embedded Design⠀⠀⠀Hardware ∙ Firmware

or

> Embedded Design — Hardware, Firmware

vs.

> Embedded Design - Hardware/Firmware

That said, everything except the first two is subjective. A relaxed vibe of “don’t give a damn about it” might be strategic if you are good at what you do (and crucially it is not design), as long as your card is legible and does its function.

You should see the font on Paul Allen's card.

My defaults are sans-serif Helvetica or Roboto, serif Roboto Serif, and monospace Fira Code

That must be very fragile! Gotta be careful when unplugging, pulling very straight.

I thought this was one of the most impressive parts of the design, had no idea this was possible.

Probably what you want is "numerical methods" and "computational physics".

"Physical simulation" is a very broad scope, so your code for simulating fluids is going to be very different from your code for simulating planetary orbits, and at times it may feel a bit ad hoc. But at its foundation physical laws are written in differential equations and linear algebra.

So whatever algorithm lets you numerically integrate several inter-related variables is going to be broadly applicable to simulating any physical phenomena. At the simplest end of the spectrum you just naively approximate integration by brute force. Eg at each step just update your physical state variables by doing velocity += acceleration, position += velocity. This is called Euler's method, and while simple, it accumulates unacceptable errors rather quickly in most circumstance. The more advanced approach is to use a method like Runge Kutta. In circumstances where you have some known property, like say energy conservation, you can implement a method which explicitly imposes the constraint. This is good for cases where the motion is highly periodic as it prevents the numerical error from accumulating exponentially in orbits that spiral out of control.

Of course at some point you'll have to grapple with the issue of if you are simulating trajectories of free particles or values of neighboring grid points in a field. This question of how best to encode physical systems and simulate them cuts to the heart of physics.

I'll leave it at the old cliche "information is physical"

Rigid body simulations are much much simpler. There’s a siggraph course from 2001 [0] which is a bit of a dense read but it will bring you all the way up to a full blown rigid body simulation and understanding the math behind it too.

[0] https://graphics.pixar.com/pbm2001/pdf/notesg.pdf

One thing that helped me was doing some tutorials for pico-8, an intentionally 'weak' game platform, one of which is a platform game with a simple / understandable inertia / gravity simulation (jumping, running left/right; think Mario). It was understandable enough with an x / y position for the character and a delta-x / delta-y representing their current speed. Every frame the dx / dy would get changed depending on player input and/or character state.

Ex: if player presses jump button, set state to 'jumping' and dy to 1. Every frame, dy = dy * 0.9. When dy <= 0, set state to 'falling'. Every frame, dy = dy * 1.1 until dy = 1 (terminal velocity). Then add some collision detection.

I think those basics are also behind the simpler physics simulations, the 'falling sand' types would be ideal for an application like this.

For statistical mechanics, I really liked [1]. Comes with loads of python programs.

To see what might peak you interest, the videos in [2] could be a good starting point.

[1]: https://www.coursera.org/learn/statistical-mechanics

[2]: https://matthias-research.github.io/pages/tenMinutePhysics/i...

Just go to Perplexity or something like that, its well trodden ground. And essentially, what you're doing is discretizing the relevant differential equations and getting that to run in a 2D or 3D cellular automaton.

I'll give you a simple example. For diffusion of heat between 2 points, the rate of change (first derivative) is proportional to the difference in temp between them. So you make an update rule for points on a grid that says "calc the average difference of a cell's temp with that of its neighbors, multiply by some constant, and that is the amount to update this cell at this time. Run that for every cell in parallel, many times." Then you tack on a visualization and you can watch the heat diffuse. A fun example would be the cooling of the proto-Earth. You can watch the crust form.

Heat diffusion is a good starter problem. So is gravitational interaction.

Essentially all physics simulations are either particle based or based on integration of differential equations (although in a computer both approaches involve a discretization which makes them somewhat computationally similar). You can consider reading through Numerical Recipes which is sort of the bible for this stuff for physicists, but it is aimed at scientific audiences with weak CS background. Something like Computer Simulation of Liquids by Allen could be a good start too. Let's be clear that the approach I'm talking about here is focused more on physical correctness: if you are a game designer it's not important that your fluid simulations are physically correct and more that it looks physically correct to a player, and there are a variety of more heuristic techniques for something like that.

The Nature of Code by Daniel Shiffman is an excellent entry point - it teaches fundamentals of physics simulations with clear examples in Processing/p5.js.

For water simulation, look towards learning compute shaders.

Eulerian (grid-based) simulation is one of the classic examples.

Electronics can be surprisingly easy and cheap to build these days. He designed the circuit and layout with software called KiCAD (free and open source) then submitted the designs to a fabrication house - probably a popular offshore one - that easily can handle that level of board and component placement complexity. It would probably cost only a few hundred to build and ship, with 1 month turnaround time.

You can also hand-assemble surface mount parts by applying solder paste carefully to the pads, then placing all the components on the paste and heating the board until all the solder melts. That would have very time consuming for all those LEDs!

>He must have worked with a company that can do the surface mount assembly

He did (there are centroid files in the production folder, which tell the board house where to put the components), but you'd be surprised at how possible it is to assemble something like this by hand. You won't believe me, but I find it easier than through-hole soldering (because you don't have to keep flipping the board over).

But there's a 99.9% chance this was done in-house at JLC or PCBWay.

You can get boards like these made for single-digit dollars per unit* even at prototype scale, through companies like jlcpcb.

*I haven't looked at the specific parts for this board, the LEDs look nice and could be a little pricey.

Yeah, wondering how the LEDs were aligned so precisely. Some kind of silicone grid-like jig to hold them while the solder reflows? Or is it just pick & place robotics doing what they do with precision?

This is so cool. I wish something like this had the ability to load your debit/credit cards into it. Advantages over using the card directly or a wallet app on your phone.

1. You don't voluntarily give your financial transaction info to big tech.

2. Your card details are hidden. So if your wallet gets stolen, less danger of fraudulent transactions.

3. Carry one heavy card instead of many light ones.

4. Don't have to memorize the pin of all the cards. Or the pin just shows on the mini screen after finger print authentication.

Do you use any of the features? This is kinda cool, I love when people pack way too many features into a single product :P

Ha! That's pretty cool.

My first thought with this card was that it could be "gamified" into something that kids would probably love. A clique-y, social thing where kids could "pour" some of their fluid into another's card, with NFC or something. User preference colors that don't change when "poured" could help indicate how many different people have interacted with your card.

But enough spitballing. There's no killer idea there. Just something I'll be amused to see show up as a value-add for some other kind of toy, or whatever.

I love it; I bought a secondhand Palm just before smartphones became a thing for cheap and had a lot of fun with it. I wonder if I still have it somewhere and whether it still works, I haven't seen it in ages though so probably not.

small ad-hoc networks like that with IR and early bluetooth were a lot of fun.

Agreed. I'd never hire this embedded system engineer to do graphic design. /s

That’s cred, man. Real cred.

Wack font. Circuits exposed. Pixels with fat borders between them. An ugly charging port. But more stuff, packed into a small sleek volume than reasonably possible. Working perfectly.

That’s not Jobs. Oh, no. It’s effing Woz.

The guy is a true hardware engineer.

It's not as thick as a usbc port, look at the picture of them charging... the usb plug is much thicker than the card.

Now, let's see Paul Allen's ultrathin business card that runs a fluid simulation.

O.4mm thick rechargeable battery:

https://www.lithium-polymer-battery.net/ultra-thin-lithium-p...

Standard credit card: 0.76mm thick

seems dangerous to have terminals of battery exposed, shorting (and with rechargeable, burning) hazard

My bad: "That's actually not the same guy. He made the pendant that this project is based on."

THANK YOU phirks for the correction. Much appreciated.

That's actually not the same guy. He made the pendant that this project is based on.

That and the overlapping silkscreen hurt to see, but otherwise a super cool project. Although they're very minor things that don't technically matter, it can give off certain impressions to people.

disagree, a nice serif font is more distinctive with most of everything using a very tight cluster of boring sans-serif fonts.

I sort of like it. Looks like a Neon Genesis Evangelion episode card

It is.

rather it's even smaller, it simply has the inner part of a usb c connector - exactly the thickness of the pcb

similar to https://github.com/cnlohr/ch32v003_3digit_lcd_usb/

In the implementation, the design uses a 'card edge' type connector with the whole PCB fitting into the constraint of the thickness of the center blade of the USB-C connector. So when charging, the board slots into the cable-end connector, and when not charging there is only the PCB. The PCB has cut-outs for the cable-end connector to fit into the PCB -- so like you're saying, but even thinner.

Thought the same but from what I can see those are somewhat uncommon, presumably you are unable to affix them to the board as securely as the typical connectors

The images in the GitHub show that the card has this.

Is a cr2032 shorting it is not dangerous, it can’t supply the current to get hot enough do any real damage.

The fluid simulation logic is split into a separate crate.

https://github.com/Nicholas-L-Johnson/flip-card/tree/main/fl...

But does it beat the Joel Bauer business card? It took 25 years to design!

https://youtube.com/watch?v=4YBxeDN4tbk

Practically pregnant with electric potential

"I can't belllieeeve RMDNZ preferred L-Johnson's card to mine"

"Silian Rail"

Yeah embassy has improved tons recently. This is because embedded Rust is receiving a lot of investment from industry, embedded engineers desperately want a real C alternative there.

He's an hardware engineer, not a software engineer.

After many years of self-hosting an email server I also came to the realization that it's not worth the hassle (in terms of maintenance / problems) and I switched to Proton Mail.

Using a custom domain with Proton Mail is not free (and all the other alternatives I know of are the same) and there's little advantage other than having a nice name. I think for a HW Engineer this is good enough.

To be fair it fits in with the Github and LinkedIn links.

You’re going to get downvoted obviously but this appeared on Embedded (or electronics?) and then made its way here. It’s a bit telling the actual hacking communities are on “that awful site” that’s so beneath us, meanwhile our pristine HN is full of gushing AI ads as front page hacker material.