Fail Of The Week: Always Check The Fuse

[Tomas] at Umeå Hackerspace in Sweden had some broken audio equipment, including a Sharp CD player/amplifier. What went wrong when he tried to fix it is a fail story from which we can all learn.

The device worked – for about a second after being turned on, before turning itself off. That’s a hopeful sign, time to start debugging. He took the small-signal and logic boards out of the circuit, leaving only power supply and amplifier, and applied the juice.

Magic blue smoke ensued, coming from the amplifier. Lacking a suitable replacement part, that was it for the Sharp.

On closer inspection it emerged that the previous owner had bypassed the power supply fuse with a piece of copper wire, Evidently they had found the fuse to be blowing too often and instead of trying to fix the problem simply shot the messenger.

We have all probably done it at some time or other. In the absence of a replacement fuse we may have guestimated the number of single strands required to take the current, or used a thin strip of foil wrapped around the fuse body. And we’ll all have laughed at that meme about using a spanner or a live round as a fuse.

So if there’s a moral to this story, it’s to always assume that everyone else is as capable as you are of doing such a dodgy fix, and to always check the fuse.

2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which celebrates failure as a learning tool. Help keep the fun rolling by writing about your own failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.

A Field Guide to the North American Utility Pole

We live under the umbrella of an intricate and fascinating web of infrastructure that enables every aspect of modern technology. But how often do we really look at it? I’ve been intrigued by utility poles for years, and I’ve picked up a thing or two that I’d like to share. Bear in mind these are just my observations from the ground in my area; I’m sure utility professionals will have better information, and regional practices will no doubt lead to very different equipment arrangements. But here’s a little of what I’ve picked up over my years as a pole geek.

Continue reading “A Field Guide to the North American Utility Pole”

Writing a FUSE Filesystem in Python


Have you ever thought a particular project could be better if you could just control the file access directly? [Stavros Korokithakis] did, specifically for a backup program he was working on. What followed was the realization that writing a FUSE filesystem, particularly in Python, isn’t as complicated as it may seem. Really, through the power of open source, the heavy lifting has already been done for us. If you’d like to try it yourself, you’ll need to install fusepy. From that point, you simply need to define the filesystem methods you will be using.

Python isn’t going to win any speed contests in the filesystem space, but that isn’t really the point. Using this technology opens up a huge opportunity for new ways of accessing data. If you let your mind wander, you can conceive of encrypted filesystems, seamless remote data access, new key-value storage designs, etc. Perhaps even more interesting is the idea of using Python to communicate with a physical device… maybe a proc filesystem to keep track of your robot telemetry? We’d love to hear your ideas in the comments.

We had success using [Stavros’] example script on Linux and OSX. (Fair warning if you’re on a Mac, the pip version of fusepy seems to be linked against fuse4x rather than OSXFUSE, but once you’ve got the prerequisites installed, you’re golden.) We didn’t have a Windows machine to test. Can anyone confirm if the same is possible there?

Non-resettable thermal fuse teardown


This component is a one-shot thermal fuse. When the body rises above the specified temperature the two leads stop conducting. They’re useful in applications like motors, where you want to make sure power is cut to an overheating piece of hardware before permanent damage happens. They’re pretty simple, but we still enjoyed taking a look inside thanks to [Fatkuh’s] video.

The metal housing is lined with a ceramic insulator, which you can see sticking out one end in the shape of a cone. It surrounds a spring which connects to both leads and is under a bit of tension. The alloy making the connections has a low melting point — in this case it’s about 70 C — which will melt, allowing the spring to pull away and break the connection. In the clip after the break [Fatkuh] uses his soldering iron to heat the housing past the melting point, tripping the fuse. He then cracks the ceramic cone to show what’s inside.

The only problem with using a fuse like this one is you’ll need to solder in a new component if it’s ever tripped. For applications where you need a fuse that protects against over current (rather than heat) a resettable polyfuse is the way to go.

Continue reading “Non-resettable thermal fuse teardown”

Doubling down on motor drivers

Motor driver chip too weak for your needs? Just use two of them. That’s the advice which [Starlino] gives. He stacks motor driver chips to product move powerful controllers.

When stacked as shown, the driver combos should be able to drive at 4A. This is partly because he ganged together the outputs in pairs, and also because of the stacking. That’s a lot of juice, but [Starlino] documented his testing stage which shows that they’re up to it. It’s a bit hard to see from this angle, but he is using a serpentine heat sink. It snakes its way between the stack of chips, then over the top chip before folding back and spreading its wings. The motors he’s using have a stall current of 3.7A, and he included resettable fuses graded at a 2A hold current. He’ll be glad to have that extra protection is something goes wrong with the drivers.

[Thanks Roger]

Fuse making machine

This is a fuse making machine that operates nearly as well as a factory machine would. Have you figured out what exactly this is yet? It’s not an electrical fuse, it’s a Visco Fuse. Still not totally clear? Don’t worry, we had to look it up too. Visco Fuse is a high-quality safety fuse used in fireworks.

[Robert McMullen] built the machine as part of his degree in Mechanical Engineering at Olin College. But there’s a hobby twist behind its genesis. When he has free time he participates in Olin’s Fire Arts Club and we’re sure this stuff comes in handy. The fuse is made by encapsulating a stream of gunpowder in a tube of woven thread. Twenty spools of thread wrap their way around the nozzle of a fine funnel. Once the casing is in place the machine coats it in a waterproof lacquer.

The image above only shows the base of the machine. All the fun parts (and test burns including one underwater) can be seen in the video after the break. Continue reading “Fuse making machine”

Resurrecting a cellphone with blown USB circuitry

[Script] is pretty lucky. One of the engineers who designed his cellphone included over-voltage protection in the circuit. Of course you probably wouldn’t know about this if there wasn’t a service schematic available. But a bit of searching around let him resurrect the fried USB segment of his Nokia N900.

Now [Script] has been experimenting with portable solar power like the system featured at 25C3 a few years back. Unfortunately he made an error which routed 12V into the USB connector’s 5V rail. After this unfortunate mistake the phone would not longer connect via USB, or charge the battery. Luickly the N900 is a favorite with the hacker community (you can see all kinds of N900 related projects here at Hackaday) and [Script] found his way to their N900 Schematic page. Digging into page four he found part F5300 which is labeled 2.0A. He removed the PCB and shielding, and tested the part with a multimeter to confirm it was blown. A quick wire bridge got the phone charging again, but [Script] plans to position a new fuse as soon as he can source the part.

Who says these devices aren’t user serviceable? If we could just get our hands on more service schematics perhaps our gear would last longer.