Passive, but not Innocuous

Maxim Integrated recently posted a series of application notes chronicling how there’s more going on than you’d think in even the simplest “passive” components. Nothing’s safe: capacitors, resistors, and even printed circuit boards can all behave in non-ideal ways, and that can bite you in the reflow-oven if you’re not aware of them.

You might already know that capacitors have an equivalent series resistance that limits how fast they can discharge, and an equivalent inductance that models departures from ideal behavior at higher frequencies. But did you know that ceramic capacitors can also act like voltage sources, acting piezoelectrically under physical stress?

For resistors, you’ll also have to reckon with temperature dependence as well as the same range of piezoelectric and inductance characteristics that capacitors display. Worse, resistors can display variable resistance under higher voltages, and actually produce a small amount of random noise: Johnson Noise that depends on the value of the resistance.

Finally, the third article in the series tackles the PCB, summarizing a lot of potential manufacturing defects to look out for, as well as covering the parasitic capacitance, leakage currents, and frequency dependence that the actual fiberglass layers themselves can introduce into your circuit.

If you’re having a feeling of déjà-vu, the same series of articles ran in 2013 in Electronic Design but they’re good enough that we hope you won’t mind the redundant repetition all over again. And if you’re already quibbling with exactly what they mean by “passive”, we feel your pain: they’re really talking about parasitic effects, but we’ll let that slide too. We’re in a giving mood today.

[via Dangerous Prototypes]

If You Could Build a Clock in World of Goo…

[Orson Scott Card] once wrote “…time flows through all lives equally.” You have to wonder what he would think if he saw Rhei, a fluid clock that is part prototype, part dynamic installation, and part moving sculpture. The developers [Damjan Stanković], and [Marko Pavlović] say that time flows, and thanks to the fluid-based numerals on the clock face, that seems to be an appropriate tag line (if you can’t visualize it, check out the video below).

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How Retractable Pens Work

[Bill Hammack], aka the [EngineerGuy] is at it again, this time explaining how retractable ballpoint pens work.

pen-thumbIn this excellent video, he describes the simple (but remarkably sophisticated) engineering of the mechanism that allows a pen to pop the ballpoint mechanism out, then back in again. It is a great example of how to illustrate and explain a complex concept, much like his videos on how the CCD sensor of your camera works.

Perhaps the most interesting part of the video is an off the cuff observation he makes, though. The Parker company, who first developed the retractable mechanism, were worried that this new design might flop. So they didn’t put the distinctive Parker arrow clip onto the pen until a few years later, when the pen was a big seller. It seems that while some engineering problems are easy to solve, short-sighted accountants are a harder problem.

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Hackaday Printing Press Upgrade

There comes a time when your movable type becomes so over-used that you no longer get a legible print off of the printing press. For months now we’ve been at work on a new site design that maintains the essence of Hackaday while ejecting the 10-year-old dregs of the site. With each small success we’ve actually ruined ourselves on viewing the old design. It is with great relief that we unveil a site design built specifically for Hackaday’s needs.

The most notable change is in the content of our landing page. For ten years, loading resulted in the most recent blog posts. The blog concept is proven, but provides little opportunity to highlight quality original content and information about upcoming events. We have tried the use of “sticky” posts but honestly I find them somewhat annoying. The solution to this is not immediately apparent, but I feel we have found the most efficient solution to our complex set of needs..

We have a lot of community members who participate in Hackaday in numerous ways. Changes found in this design are driven by that fact. The landing page will, from this point forward, be a somewhat more persistent collection of notable content from the blog, our community site (, as well as news regarding live events, store features, contest highlights, and more. Those hard-core fans — a label I also assign to myself — will find the same reading experience as always on the new blog URL:

Aesthetically, we hope that all will agree the new design far supersedes the old. There was a lot to fix, and the work of the Hackaday crew who designed and implemented this new interface is truly amazing. I hope you will take the time to leave a positive comment about their work. As with any major transition, there will be some bumps in the road. Right now most of our sidebar widgets have not been migrated but that and any other problems will be fixed soon.

In this design we strived to highlight the title and image of each post to immediately convey the core concepts of the projects shown here. The author by-line and comment count remain core to the presentation of the articles, and our link style continues to be immediately apparent in the body of each article. I think we have far surpassed the readability of the comments section, in addition to the content itself. We knew we could rebuilt it… we have the technology… long live articles worth reading.

UPDATE: We are working very hard to fix all the parts that don’t look quite right. Thanks for your patience!

UPDATE 2: Infinite scrolling isn’t a feature, it’s a regression. On our test server all the blog listings were paginated just like always. When our host, WordPress VIP, pushed live the infinite scrolling manifested itself. We’ve filed a ticket with them and are hoping for a solution shortly.

UPDATE 3: Infinite scrolling has now been fixed and the blog layout now paginates. The mouse-over zoom effect has been removed. Slideshow speed has been adjusted and if you hover you mouse over a feature it will pause the scrolling.

Developed on Hackaday: License Incompatibilities and Project State

mooltipass top pcb

It has been a while since we wrote an article about our ongoing offline password keeper project, aka the Mooltipass. Our last post was asking our dear readers to vote for their favorite card art, so what have we been doing since then?

For the last few weeks we’ve mostly been improving our current PCBs and case design for the production process to go smoothly. The final top PCB shown above has been tweaked to improve his capacitive touch sensing capabilities, you may even see a video of the system in action in the Mooltipass project log on We’ve also spent some time refining the two most popular card art designs so our manufacturers may print them correctly. We’ll soon integrate our updated USB code (allowing the Mooltipass to be detected as a composite HID keyboard / HID generic) into the main solution which will then allow us to work on the browser plugin.

It’s also interesting to note that we recently decided to stop using the GPL-licensed avrcryptolib. Our current project is CDDL licensed, allowing interested parties to use our code in their own project without forcing them to publish all the remaining code they created. The GPL license enforces the opposite, we therefore picked another AES encryption/decryption implementation. This migration was performed and checked by our dedicated contributor [Miguel] who therefore ran the AES NESSIE / CTR tests and checked their output, in less than a day.

We’re about to ship the first Mooltipass prototypes to our active contributors and advisers. A few weeks later we’ll send an official call for beta testers, just after we shown (here on Hackaday) what the final product looks like. Don’t hesitate to ask any question you may have in the comments section, you can also contact us on the dedicated Mooltipass Google group.

Developed on Hackaday: Vote for your Favorite Card Art

A few weeks ago we asked our dear readers if they were interested in coming up with some card art for the Mooltipass project. We received more than a dozen of them and a few days ago the HaD project Mooltipass followers/Mooltipas Google group recipients voted for their favorite ones.

Today we’ll present you the three popular ones and ask you to pick your favorite, so please follow us after the break…

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Developed on Hackaday: Olivier’s Design Rundown

The Hackaday writers and readers are currently working hand-in-hand on an offline password keeper, the Mooltipass. A few days ago we presented Olivier’s design front PCB without even showing the rest of his creation (which was quite rude of us…). We also asked our readers for input on how we should design the front panel. In this new article we will therefore show you how the different pieces fit together in this very first (non-final) prototype… follow us after the break!

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