Linux Fu: Tracing System Calls

April 7, 2020 by 11 Comments

One of the nice things about Linux and similar operating systems is that you can investigate something to any level you wish. If a program has a problem you can decompile it, debug it, trace it, and — if necessary — even dig into the source code for the kernel and most of the libraries the program is probably using. However, the tools to do this aren’t ones you use every day. One very interesting tool is strace. Using it you can see what system calls any program makes and that can sometimes give you important clues about how the program works or, probably more often, why it doesn’t work.

Let’s consider the least complex use of the command. Suppose you want to make symlink from testxmit.grc to the /tmp directory. That command is simple:

ln -sf testxmit.grc /tmp

But if you tell strace to run it, the command becomes:

strace ln -sf testxmit.grc /tmp

You might want to redirect the output to a file using the shell or the -o option, though. Some commands generate a lot and often the first page or two of output isn’t really what you care about anyway. Continue reading “Linux Fu: Tracing System Calls” →

Nixie Clock Turns Boombox

April 7, 2020 by 12 Comments

With all the Nixie Clock projects out there, it is truly difficult to come up with something new and unique. Nevertheless, [TheJBW] managed to do so with his Ultimate Nixie Internet Alarm Clock (UNIAC) which definitely does not skimp on cool features.

Although the device does tell time, it is actually a portable boombox that streams music from Spotify using a Raspberry Pi Zero running Mopidy. The housing made from smoked acrylic, together with the IN-12A Nixie Tubes, an IN-13 VU meter, and illuminated pushbuttons give this boombox kind of a 70s/90s mashup retro look. The acrylic housing is special since it consists of only two plates which were bent into shape, resulting in smooth edges in contrast to the often used finger or T-slot design.

For his project [TheJBW] designed a general-purpose Nixie display that can not only show time and date but also the elapsed or remaining track time. He also came up with a Python generated artificial voice that reads you the current playlist. The only problem [TheJBW] has run into was when trying to design a suitable battery system for the device, as the high current draw during start-up can easily cause brownouts. Due to time constraints, he ended up with a MacGyver-style solution by taping a 12 V battery pack from Amazon to the back of the unit.

Among the large variety of Nixie projects we don’t think we have ever seen them in an audio player before except for some attempts of using them as an amplifier. However, it is known that IN-13 tubes make a great VU meter.

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Art of 3D printer in the middle of printing a Hackaday Jolly Wrencher logo

3D Printering: When Resin Printing Gets Smelly

April 7, 2020 by 20 Comments

Nowadays, resin printers are highly accessible and can do some great stuff. But between isopropyl alcohol for part rinsing and the fact that some resins have a definite smell to them, ventilation can get important fast. The manufacturers don’t talk much about this part of the resin printing experience, but it’s there nevertheless. So what can be done when smells become a problem?

I recently had to deal with this when I printed several liters of resin worth of parts. That’s a lot of resin, and a lot of alcohol for part washing. Smells — which had never been much of a problem in my work area — suddenly became an issue.

Where Odors Come From

Smells come from two sources: the resin itself, and the isopropyl alcohol used for cleanup and part washing. Continue reading “3D Printering: When Resin Printing Gets Smelly” →

Real Engineering Behind Ventilators

April 7, 2020 by 40 Comments

Experts on cognition tell us that most people think they know more than they really do. One particular indicator for that is if someone is an expert in one field and they feel like all other fields relate to theirs (everything boils down to math or chemistry or physics, for example). This causes them to be overconfident on things they don’t actually know about. When it became clear that the current virus crisis might lead to a shortage of ventilators, many electronic experts set about to design low-cost easy to replicate ventilators. How hard is it, after all, to squeeze a bag once every few seconds? But it turns out, there are a lot of details you need to know to do it right. [Real Engineering] and [Real Science] joined to create an excellent video that covers a lot of what you need to know. You can see the video below. The video shows a few designs that — while motivated by altruism — would probably do more harm than good if used on real patients.

The video’s creator is a biomedical engineer who worked in the past for Medtronic — a maker of ventilators who, by the way, recently open-sourced one of their designs. They also had [Dr. Rohin Francis], who has a medical YouTube channel, fact check the video. and provide some on-screen background We learned a few new medical terms and found that a high-end ventilator made in one factory gets built at about 225 per week. They think they can increase to 500.

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Reliability Check: Consumer And Research-Grade Wrist-Worn Heart Rate Monitors

April 7, 2020 by 12 Comments

Wearables are ubiquitous in today’s society. Such devices have evolved in their capabilities from step counters to devices that measure calories burnt, sleep, and heart rate. It’s pretty common to meet people using a wearable or two to track their fitness goals. However, a big question remains unanswered. How accurate are these wearable devices? Researchers from the Big Ideas Lab evaluated a group of wearables to assess their accuracy in measuring heart rate.

Unlike other studies with similar intentions, the Big Ideas Lab specifically wanted to address whether skin color had an effect on the accuracy of the heart rate measurements, and an FDA-cleared Bittium Faros 180 electrocardiogram was used as the benchmark. Overall, the researchers found that there was no difference in accuracy across skin tones, meaning that the same wearable will measure heart rate on a darker skin-toned individual the same as it would on a lighter skin-toned. Phew!

However, that may be the only good news for those wanting to use their wearable to accurately monitor their heart rate. The researchers found the overall accuracy of the devices relative to ECG was a bit variable with average errors of 7.2 beats per minute (BPM) in the consumer-grade wearables and 13.9 BPM in the research-grade wearables at rest. During activity, errors in the consumer-grade wearables climbed to an average of 10.2 BPM and 15.9 in the research-grade wearables. It’s interesting to see that the research-grade devices actually performed worse than the consumer devices.

And there’s a silver lining if you’re an Apple user. The Apple Watch performed consistently better than all other devices with mean errors between 4-5 BPM during rest and during activity, unless you’re breathing deeply, which threw the Apple for a loop.

So, it seems as if wrist-worn heart rate monitors still have some work to do where accuracy is concerned. Although skin tone isn’t a worry, they all become less accurate when the subject is moving around.

If you’d like to try your own hand with fitness trackers, have a look at this completely open project, or go for the gold standard with a wearable DIY ECG.

Help Save The National Videogame Museum

April 6, 2020 by 16 Comments

The National Videogame Museum in Sheffield, UK, houses a unique collection celebrating all decades of video games and their culture, and as the lockdown has brought with it a crisis threatening its very existence, has launched a crowdfunding campaign with a video we’ve placed below the break. As a relatively young organisation, they have yet to build up the financial buffer that a more established one would have. It’s important that this and other heritage sites live to open again another day, so we’d urge you to take a look.

On their website they’re providing a page of activities for the bored youngster in your life, but to whet your appetite should you wish to visit them in the future they also have a selection of pages about the rest of their exhibition.

One of the sad features of living through  a pandemic comes in knowing that some of the businesses and organisations we hold dear might not make it through the crisis. We’ve put in a few orders to smaller suppliers over the last week or two to shove a bit of extra business their way, and no doubt you have too. What is not so easy however, is when the threatened organisation is a visitor attraction; we can’t make the trip during a lockdown. The NVM is unlikely to be the only such attraction facing the pinch, so we’d urge you to look out for those that are close to you as well.

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Compiling C To PowerPoint

April 6, 2020 by 5 Comments

If you have worked for a large company — or even a small one — it might seem that you spend more time writing PowerPoint charts than programming. [Tom Widenhain’s] video asks the question: Can we compile C into PowerPoint? Watch the video below to find out the answer. Would it surprise you to know that [Tom] wanted to simulate the x86? It surprised us, too, and we had to note the video appeared on April 1. It does look workable, though, other than it is a bit unwieldy.

Instead of a Turing machine, this builds a set of clever logic gates. Unsurprisingly, [Tom] is the guy who put together a Turing machine in Excel. Surprisingly, he isn’t the first one to attempt a C to PPT compiler. The University of Chicago had a similar idea over a year ago, based on [Tom’s] earlier work and executed program using inefficient Turing machines.

Continue reading “Compiling C To PowerPoint” →