> 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.

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.

* less joy of doing hard things

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

Disadvantages:

  * excessively fast fluid motion at card scale

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

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'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.

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

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.

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

Practically pregnant with electric potential

"Silian Rail"

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

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

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

Could as well display the name and/or email, if rotated just so.

That's a good idea!

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

+1 for mitxela, dude never ceases to amaze

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"

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...

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.

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.

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.

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.

There's a BOM, you can find out. Plus some peanuts for the PCB :)

Now whether you get it populated or not..

https://github.com/Nicholas-L-Johnson/flip-card/blob/main/ki...

I'm just imagining interviewing a candidate for a job involving embedded systems and this dude pulls this out at the end and says "If you have any other questions, my email's right on there."

What an absolute baller this guy is.

I am thinking how most of the people I get business cards from are people I've already invited in to my office and are discussing some potential business relationship. They've often flown to my city, staying in a hotel, paying for transport, meals, etc. The impression they make during that 1 hour meeting is paramount and I think this is certainly going to leave a lasting impression. Most of those business cards just get tossed into a drawer or trash bin, I bet people keep this one on their desk a play around with it.

That’s a funny way to try and get people to get back in touch with you, haha.

This is true.

I remember a story linked from here, recently, where a designer submitted a CV that was a custom-made widget of some kind.

He got the job.

I don't know, I struggle with a light switch, but that doesn't look like board someone took home with a box of parts and a soldering iron to make at home.

Are there services that you can send the BOM and board files too, and not only do you get the PC board back, but it's populated? Will they do that for a onesy-twosy thing like this?

Then all you have to do is supply the battery and download the firmware (however that is done).

I tried, that's why it's 21x21. Still haven't managed to get it to read.

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.

Is there a Digital Disco Ball?

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

The circle works much better for the fluid simulation.

Wow that's a nice design.

£1200 for one though.. oof.

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.

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.

Starting point: Ocean waves in a bottle

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

Exactly my thought. Just make it a desk toy.

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.

* no rust

Giving the actual card though leaves a feeling of guilt... sort of like those old surveys you would receive in the mail, with a $1 bill included. A hyperlink is forgettable.

Or give out a regular paper business card with a QR code on it pointing to your resume website...

snicker

The fluid simulation logic is split into a separate crate.

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

For water simulation, look towards learning compute shaders.

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

Some conformal coating spray would probably be all that’s needed.

Just as a point of interest perhaps for folks who are not familiar with PCB design and modern electronics: the "huge" matrix of 21x21=441 LEDs would, with the specified LED from the bill of materials (BOM) cost all of $6.

That is based on the price for low quantity (1-500 pieces) though; if you were to build more than one board you would buy more LEDs, pushing the per-LED price (way) down. You can get 4,000 LEDs for $30.'

Edit: here is the LED in question, from the BOM [1].

[1]: https://jlcpcb.com/partdetail/C497920

(This assumes that the guy passed through the resume filters and advanced to the in-person stage, which is not that easy. Should work on a video call though.)

Feed your animal by calling me once a month to check in (and get the monthly "food code")

increase viscosity of said fluid

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.

I only mention this because this was posted here at, approximately, 08:00 EST 2028-08-08, and posted on Reddit at, approximately, 00:00 EST 2028-08-08.

Still has to respond "no" on the post interview scorecard because the given solution didn't use the optimal ObscureLeetCodeAlgorithm

This matches my experience fairly accurately except for the one guy I met at a housewarming who handed out cards to everyone. It was so weird - I haven’t seen anyone do that in real life. He had a shop that repairs chipped windshields.

And you know what? About 8 months later my windshield got sprayed by gravel. That guy got the business (he’s a friend of a friend after all, and I had his number in my wallet).

I’d say the issue isn’t that cards are outdated. It’s that people aren’t using them correctly.

In the way back days when we submitted our CVs on paper, I always cut mine to a smaller size than letter, in a branded folder. People tend to stack things with the smaller items on top. I don't know if mine actually was on top of the stack, but I can say that I basically always got the contract.

Yes, I’ve done it for a batch of 10 with https://jlcpcb.com/smt-assembly for around $10/board including the PCB

Those little cube world blocks were neat: https://corporate.mattel.com/brand-portfolio/cube-world

Maybe I grew out of the age range or maybe the whole market of silly knick-knacks has died out but they definitely drove my interest in all things electronic.

The C in CR2032 means lithium fwiw. As in it's lithium either way.

The LiR2032 (rechargable lithium) are slightly higher voltages but pretty much the same total energy.

Fwiw if you ever have electronics that require 3V minimums the LiR2023 is better than the CR2032 since it's 3.7V vs 3V in the same form factor. It's common knowledge that the ESP32 for example can glitch on a CR2023 since it needs 3V minimum but it'll actually run fine on a LiR2032.

Yep, the rechargeables of this form factor are also pretty safe. They just don’t have much current capacity, as they are meant for long life (years) and long current draw.

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

I have what I call my “Victorian Calling Cards.” I’m retired, and have no need to advertise or boast.

They are fairly fancy moo.com cards, with my name, email, and cellphone. Nothing else.

On the back, is a fancy “dragon head” logo (the one you see, if you look at most of my social media accounts). It’s actually my old artist signature. It’s over a burnt umber gradient.

People like them, and use them.

Nice one. 28800 pounds :O

For most of us makers it's very hard to make money as our things sell for so little that it's like 3€ per hour to make them. Kudos to this guy, he really does his marketing right.

I bought one recently and none of the provided code samples would compile. Zero support.

The render is pretty gnarly, but it's not quite that bad in person

https://github.com/Nicholas-L-Johnson/flip-card/blob/main/me...

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.

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

I might be wrong, but you might need need (at least) a 23x23 LED matrix to have a white border around the outside to give it the contrast needed (the "quiet zone", since QR data is black).

I had an ad on Facebook marketplace for a synthesizer. The guy who bought it gave me his business card - cloud architect for a competitor. He didn't give it to me because we were in similar field - we had a pleasant conversation over shareEd hobby and he gave it to me then, after which I realized we were in same field, so clearly he gave them around a lot.

If I consider changing jobs, or if I need those very particular services he's getting a call :-).

Definitely still a market for regular cheaper business cards for stuff like this. I regularly keep cards of people like this were I might need their service in the future, but they don’t need to be fancy at all and I don’t think it really adds much value when they are. The market for “good service” in trade type labor that I’d always hire a guy I have even a weak social connection with over some random person I found online. I feel like there’s a higher chance of them not price gouging and caring about the workmanship.

But, I don’t think he’d be handing out $20 BOM cards that freely. I was more validating that there is still probably a market of people where $20 cards might make sense. As in the example I posed, a business card isn’t providing any additional information. By the time I meet these people in my office, we’ve already exchanged emails and had some conversations on the phone and are acquainted. That’s what led to the in-person meeting. I know their names and have them in my contacts.

But, just as it felt like a social faux pas to receive a business card at a housewarming party, I think it also feels like a faux pas to meet someone in a business environment (where you are the selling party) and not give out a card during the initial first handshake interaction. This is a pretty low volume and high value moment for that person so a $20 card is no big deal and could easily make sense.

I believe Sears famously used that same move (probably close to 100 years ago) to cause their catalogs to be stacked right on top of the Montgomery Ward one!

Unless the case is iron.

The card is so impressive that it doesn’t matter much, but I think that if you remove half of the text in that card and make it very legible it would burn your name into people’s brain.

This is why my first prototype had a white border around it. The LEDs were red back then, so I don't know exactly what I was thinking, but I was aware of the problem.

https://github.com/Nicholas-L-Johnson/flip-card/blob/main/me...

ah I see, its still several times thicker than a business card though.

so is it ultrathin relative to a phone?

Is this any better? I hid the vias

https://github.com/Nicholas-L-Johnson/flip-card/blob/main/me...

https://github.com/Nicholas-L-Johnson/flip-card/blob/main/me...

It doesn't work that way, unfortunately. The virtual fluid represented by the LEDs does not move anything like syrup. It's like looking at a small image of water sloshing in a big tank.

To get of fluid to behave that way on the scale of several inches, the fluid would have to be massive (very dense) while simultaneously gravity would have to be reduced.

The card should not have any text on it, but show his info on the screen when the card is first shaken, and after it has been held still for 4 seconds, before going to sleep after another 10 seconds of no motion.

> the fluid would have to be massive (very dense) while simultaneously gravity would have to be reduced.

/joy of doing hard things intensifies

You can use two different fluids instead of water and air.

I personally think it is better and I like it a lot more. On the other side the concise “Shake Me” is fun, and “Powered by Rust” makes sense there. Curious how would it look when in physical form…

Thanks for all the help. I'll be ordering this soon and I'll be sure to post it.