fail of the week

99 Articles

Fail Of The Week: Padlock Purports To Provide Protection, Proves Pathetic

January 21, 2020 by 49 Comments

Anyone in the know about IoT security is likely to steer clear of a physical security product that’s got some sort of wireless control. The list of exploits for such devices is a long, sad statement on security as an afterthought, if at all. So it’s understandable if you think a Bluetooth-enabled lock is best attacked via its wireless stack.

As it turns out, the Master 5440D Bluetooth Key Safe can be defeated in a few minutes with just a screwdriver. The key safe is the type a realtor or AirBnB host would use to allow access to a property’s keys. [Bosnianbill] embarked on an inspection of the $120 unit, looking for weaknesses. When physical attacks with a hammer and spoofing the solenoids with a magnet didn’t pay off, he decided to strip off the resilient skin that Master so thoughtfully provided to prevent the box from marring the finish of a door or gate. The denuded device thus revealed its awful secret: two Phillips screws, each securing a locking shackle to the cover. Once those are loose, a little prying with a screwdriver is all that’s need to get the keys to the kingdom.

In a follow-up video posted later, [Bill] took a closer look at another key safe and found that Master had made an anemic effort to fix this vulnerability with a squirt of epoxy in each screw head. It’s weak, at best, since a tap with a hammer compresses the gunk enough to get a grip on the screw.

We really thought [Bosnianbill]’s attack would be electronic, like that time [Dave Jones] cracked a safe with an oscilloscope. Who’d have thought a screwdriver would be the best way past the wireless stack?

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Fail Of The Week: Thermostat Almost Causes A House Fire

January 8, 2020 by 63 Comments

Fair warning: any homeowners who have thermostats similar to the one that nearly burned down [Kerry Wong]’s house might be in store for a sleepless night or two, at least until they inspect and perhaps replace any units that are even remotely as sketchy as what he found when he did the postmortem analysis in the brief video below.

The story begins back in the 1980s, when the Southern New England area where [Kerry] lives enjoyed a housing boom. Contractors rushed to turn rural farmland into subdivisions, and new suburbs crawled across the landscape. Corners were inevitably cut during construction, and one common place to save money was the home’s heating system. Rather than engage an HVAC subcontractor to install a complicated heating system, many builders opted instead to have the electricians install electric baseboards. They were already on the job anyway, and at the time, both copper and electricity were cheap.

Fast forward 40 years or so, and [Kerry] finds himself living in one such house. The other night, upon catching the acrid scent of burning insulation, he followed his nose to the source: a wall-mounted thermostat for his electric baseboard. His teardown revealed burned insulation, bare conductors, and scorched plastic on the not-so-old unit; bearing a 2008 date code, the thermostat must have replaced one of the originals. [Kerry] poked at the nearly combusted unit and found the root cause: the spot welds holding the wires to the thermostat terminal had become loose, increasing the resistance of the connection. As [Kerry] points out, even a tenth of an ohm increase in resistance in a 15 amp circuit would dissipate 20 watts of heat, and from the toasty look of the thermostat it had been a lot more than that.

The corner-cutting of the 1980s was nothing new, of course – remember the aluminum wiring debacle? Electrical fires are no joke, and we’re glad [Kerry] was quick to locate the problem and prevent it from spreading.

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Fail Of The Week: Ambitious Vector Network Analyzer Fails To Deliver

December 31, 2019 by 18 Comments

If you’re going to fail, you might as well fail ambitiously. A complex project with a lot of subsystems has a greater chance of at least partial success, as well as providing valuable lessons in what not to do next time. At least that’s the lemonade [Josh Johnson] made from his lemon of a low-cost vector network analyzer.

For the uninitiated, a VNA is a versatile test instrument for RF work that allows you to measure both the amplitude and the phase of a signal, and it can be used for everything from antenna and filter design to characterizing transmission lines. [Josh] decided to port a lot of functionality for his low-cost VNA to a host computer and concentrate on the various RF stages of the design. Unfortunately, [Josh] found the performance of the completed VNA to be wanting, especially in the phase measurement department. He has a complete analysis of the failure modes in his thesis, but the short story is poor filtering of harmonics from the local oscillator, unexpected behavior by the AD8302 chip at the heart of his design, and calibration issues. Confounding these issues was the time constraint; [Josh] might well have gotten the issues sorted out had the clock not run out on the school year.

After reading through [Josh]’s description of his project, which was a final-year project and part of his thesis, we feel like his rating of the build as a failure is a bit harsh. Ambitious, perhaps, but with a spate of low-cost VNAs coming on the market, we can see where he got the inspiration. We understand [Josh]’s disappointment, but there were a lot of wins here, from the excellent build quality to the top-notch documentation.

Fail Of The Week: Z-Tape Is No Substitute For Solder

November 26, 2019 by 36 Comments

Here at Hackaday, we see all kinds of mechanical construction methods. Some are impressively solid and permanent, while others are obviously temporary in nature. The latter group is dominated by adhesives – sticky stuff like cyanoacrylate glue, Kapton tape, and the ever-popular hot glue. They’ve all got their uses in assembling enclosures or fixing components together mechanically, but surely they have no place in making solid electrical connections, right?

Maybe, maybe not. As [Tom Verbeure] relates, so-called Z-tape just might be an adhesive that can stand in for solder under certain circumstances. Trouble is, he couldn’t find the right conditions to make the tape work. Z-tape, more properly called “Electrically Conductive Adhesive Transfer Tape 9703”,  derives its nickname from the fact that it’s electrically conductive, but only in the Z-axis. [Tom] learned about Z-tape in [Joe FitzPatrick]’s malicious hardware prototyping workshop at the 2019 Hackaday Superconference, and decided to put it to the test.

A card from a Cisco router served as a testbed thanks to an unpopulated chip footprint. The 0.5-mm pin spacing on the TSOP-48 chip was within spec for the Z-tape, but the area of each pin was 30 times smaller than the recommended minimum bonding area. While the chip was held down mechanically by the Z-tape, only five of the 48 pins were electrically connected to the pads. Emboldened by the partial success, [Tom] tried a 28-pin SOIC chip next. The larger pins and pads were still six times smaller than the minimum, and while more of the pins ended up connected by the tape, he was unable to make all 28 connections.

Reading the datasheet for the adhesive revealed that constant pressure from a clamp or clip might be necessary for reliable connections, which suggests that gluing down SMD chips is probably not the best application for the stuff. Still, we appreciate the effort, and the fine photomicrographs [Tom] made showing the particles within the Z-tape that make it work – at least in some applications.

Fail Of The Week: The 3D Printer Nozzle Wipe That Won’t

November 20, 2019 by 56 Comments

Some of you will be familiar with the idea of using a brush as a nozzle wipe on a 3D printer. The idea is that passing the hot end over the brush cleans any stray plastic from the nozzle, ensuring that those plastic bits don’t end up in unwelcome places. [Mark Rehorst] attempted to implement a nozzle brush system in his own printer, but hasn’t so far been successful.

One of the things [Mark] makes is 3D printed lamp shades and this led to his experiments in setting up an automatic nozzle cleaner. Despite best efforts, the hot ends of 3D printers can occasionally accumulate bits of molten plastic which can sometimes end up deposited on the print. Because the lamp shades are so thin and so big, having a charred blob end up on the print is pretty unwelcome. Having the nozzle automatically wiped clean would be a very handy feature, but is proving to be a troublesome one.

[Mark] based his design on a small, dense wire brush used for cleaning the print nozzle of a Stratasys printer. Sadly, he found no combination of motion or brush height that got the nozzle reliably clean every time. Sometimes a blob would be dislodged, but the hot end would pick it back up again on subsequent passes. You can see it in slow motion from a variety of angles in the video below.

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Fail Of The Week: How Not To Re-Reflow

October 10, 2019 by 30 Comments

There’s no question that surface-mount technology has been a game-changer for PCB design. It means easier automated component placement and soldering, and it’s a big reason why electronics have gotten so cheap. It’s not without problems, though, particularly when you have no choice but to include through-hole components on your SMT boards.

[James Clough] ran into this problem recently, and he tried to solve it by reflowing through-hole connectors onto assembled SMT boards. The boards are part of his electronic lead screw project, an accessory for lathes that makes threading operations easier and more flexible. We covered the proof-of-concept for the project; he’s come a long way since then and is almost ready to start offering the ELS for sale. The PCBs were partially assembled by the board vendor, leaving off a couple of through-hole connectors and the power jack. [James]’ thought was to run the boards back through his reflow oven to add the connectors, so he tried a few experiments first on the non-reflow rated connectors. The Phoenix-style connectors discolored and changed dimensionally after a trip through the oven, and the plastic on the pin headers loosened its grip on the pins. The female header socket and the power jack fared better, so he tried reflowing them, but it didn’t work out too well, at least for the headers. He blames poor heat conduction due to the lack of contact between the board and the reflow oven plate, and we agree; perhaps an aluminum block milled to fit snugly between the header sockets would help.

Hats off to [James] for trying to save his future customers a few steps on assembly, but it’s pretty clear there are no good shortcuts here. And we highly recommend the electronic leadscrew playlist to anyone interested in the convergence of machine tools and electronics.

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Fail Of The Week: How Not To Light Pipe

August 19, 2019 by 17 Comments

You’d think that something made out of glass and epoxy would transmit a decent amount of light. Unfortunately for [Jeremy Ruhland], it turns out that FR4 is not great light pipe material, at least in one dimension.

The backstory on this has to do with #badgelife, where it has become popular to reverse mount SMD LEDs on areas of PCBs that are devoid of masking, allowing the light to shine through with a warm, diffuse glow – we’ve even featured a through-PCB word clock that uses a similar technique to wonderful effect. [Jeremy]’s idea was to use 0603 SMD LEDs mounted inside non-plated through-holes to illuminate the interior of the board edgewise. It seems like a great idea, almost like the diffusers used to illuminate flat displays from the edge.

Sadly, the light from [Jeremy]’s LEDs just didn’t make it very far into the FR4 before being absorbed – about 15 mm max. That makes for an underwhelming appearance, but all is certainly not lost. Valuable lessons about PCB design were had, like exactly how to get a fab to understand what you’re trying to do with non-plated holes and why you want to fence the entire edge of the board in vias. But best of all, [Jeremy] explored what’s possible with Oreo construction, and came away with ideas for other uses of the method. That counts as a win in our book.