Statistics and Hacking: An Introduction to Hypothesis Testing

In the early 20th century, Guinness breweries in Dublin had a policy of hiring the best graduates from Oxford and Cambridge to improve their industrial processes. At the time, it was considered a trade secret that they were using statistical methods to improve their process and product.

One problem they were having was that the z-test (a commonly used test at the time) required large sample sizes, and sufficient data was often unavailable. By studying the properties of small sample sizes, William Sealy Gosset developed a statistical test that required fewer samples to produce a reasonable result. As the story goes though, chemists at Guinness were forbidden from publishing their findings.

So he did what many of us would do: realizing the finding was important to disseminate, he adopted a pseudonym (‘Student’) and published it. Even though we now know who developed the test, it’s still called “Student’s t-test” and it remains widely used across scientific disciplines.

It’s a cute little story of math, anonymity, and beer… but what can we do with it? As it turns out, it’s something we could probably all be using more often, given the number of Internet-connected sensors we’ve been playing with. Today our goal is to cover hypothesis testing and the basic z-test, as these are fundamental to understanding how the t-test works. We’ll return to the t-test soon — with real data. Continue reading “Statistics and Hacking: An Introduction to Hypothesis Testing”

Precision Pantograph Probes PCBs

Electronic components are getting smaller and for most of us, our eyesight is getting worse. When [Kurt] started using a microscope to get a better view of his work, he realized he needed another tool to give his hands the same kind of precision. That tool didn’t exist so he built it.

The PantoProbe is a pantograph mechanism meant to guide a probe for reaching the tiny pads of his SMT components. He reports that he has no longer has any trouble differentiating pins 0.5 mm apart which is the diameter of the graphite sticks in our favorite mechanical pencils.

[Kurt] has already expanded his machine’s capability to include a holder for a high-frequency probe and even pulleys for a pick-and-place variation. There’s no mention of dual-wielding PantoProbes as micro-helping-hands but the versatility we’ve seen suggests that it is only a matter of time.

Four bar linkages are capable of some incredible feats and they’re found all around us. Enjoy one of [Kurt]’s other custom PCBs in his Plexitube Owl Clock, or let him show you to make 3D objects with a laser engraver.

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Innovating A Better Printing Platform

Just because you have a fancy new 3D printer doesn’t mean that innovation should stop there. Almost everyone has had a print go foul if the first layer doesn’t properly adhere to the printing platform — to say nothing of difficulty in dislodging the piece once it’s finished. Facing mixed results with some established tricks meant to combat these issues, [D. Scott Williamson] — a regular at Chicago’s Workshop 88 makerspace — has documented his trials to find a better printer platform.3D Printer Steel Print Plate 1

For what he had (a printer without a heated plate), painter’s tape and hairspray wasn’t cutting it, especially when it came time to remove the print as the tape wouldn’t completely come off the part. How then, to kill two birds with one stone? Eureka! A flexible metal covering for the printing plate.

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An Overview Of The Dreaded EMC Tests

There is one man whose hour-long sessions in my company give me days of stress and worry. He can be found in a soundless and windowless room deep in the bowels of an anonymous building in a town on the outskirts of London. You’ve probably driven past it or others like it worldwide, without being aware of the sinister instruments  that lie within.

The man in question is sometimes there to please the demands of the State, but there’s nothing too scary about him. Instead he’s an engineer and expert in electromagnetic compatibility, and the windowless room is a metal-walled and RF-proof EMC lab lined with ferrite tiles and conductive foam spikes. I’m there with the friend on whose work I lend a hand from time to time, and we’re about to discover whether all our efforts have been in vain as the piece of equipment over which we’ve toiled faces a battery of RF-related tests. As before when I’ve described working on products of this nature the specifics are subject to NDAs and in this case there is a strict no-cameras policy at the EMC lab, so yet again my apologies as any pictures and specifics will be generic.

There are two broadly different sets of tests which our equipment will face: RF radiation, and RF injection. In simple terms: what RF does it emit, and what happens when you push RF into it through its connectors and cables? We’ll look at each in turn as a broad overview pitched at those who’ve never seen inside an EMC lab, sadly there simply isn’t enough space in a Hackaday article to cover every nuance.

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Retrotechtacular: Rocket Sleds

If you need to test rockets, missiles, or ejection-seat systems, your first instinct would be to shoot them up in the air and see what happens. But if you want data, film footage, or the ability to simply walk away from a test, you might consider running your experiment on a rocket sled.

The Holloman High Speed Test Track is a 15 km long stretch of meticulously straight railroad track located in the middle of the New Mexico desert, and bristling with measurement equipment. Today’s Retrotechtacular video (embedded below) gives you the guided tour. And by the way, the elderly colonel who narrates? He doesn’t just run the joint — he was one of the human test subjects put on a rocket sled to test the effects of high acceleration on humans. You can see him survive a run around 1:00 in. Continue reading “Retrotechtacular: Rocket Sleds”

Design and Testing of the Form 2

Formlabs makes a pretty dang good SLA printer by all accounts. Though a bit premium in the pricing when compared to the more humble impact of FDM printers on the wallet, there’s a bit more to an SLA printer. The reasoning becomes a bit more obvious when reading through this two part series on the design and testing of the Form 2.

It was interesting to see what tests they thought were necessary to ensure the reliable operation of the machine. For example the beam profile of every single laser that goes into a printer is tested to have the correctly shaped spot. We also thought the Talcum powder test was pretty crazy. They left a printer inside a sandblast cabinet and blasted it with Talcum powder to see if dust ingress could cause the printer to fail; it didn’t.

The prototyping section was a good read. Formlabs was praised early on for the professional appearance of their printers. It was interesting to see how they went from a sort of hacky looking monstrosity to the final look. They started by giving each engineer a Form 1 and telling them to modify it in whatever way they thought would produce a better layer separation mechanism. Once they settled on one they liked they figured out how much space they’d need to hold all the new mechanics and electronics. After that it was up to the industrial designer to come up with a look that worked.

They’re promising a third part of the series covering how the feedback from beta testing was directed back into the engineering process. All in all the Form 2 ended up being quite a good printer and the reviews have been positive. The resin from Formlab is a little expensive, but unlike others they still allow users to put the printer in open mode and use other resin if they’d like. It was cool to see their engineering process.

The Art of Making A Nixie Tube

Three years ago we covered [Dalibor Farnby]’s adventures in making his own Nixie tubes. Back then it was just a hobby, a kind of exploration into the past. He didn’t stop, and it soon became his primary occupation. In this video he shows the striking process of making one of his Nixie tubes.

Each of his tubes get an astounding amount of love and attention. An evolution of the process he has been working on for five years now. The video starts with the cleaning process for the newly etched metal parts. Each one is washed and dried before being taken for storage inside a clean hood. The metal parts are carefully hand bent. Little ceramic pins are carefully glued and bonded. These are used to hold the numbers apart from each other. The assembly is spot welded together.

In a separate cut work begins on the glass. The first part to make is the bottom which holds the wire leads. These are joined and then annealed. Inspection is performed on a polariscope and a leak detector before they are set aside for assembly. Back to the workbench the leads are spot welded to the frame holding the numbers.

It continues with amazing attention to detail. So much effort goes into each step. In the end a very beautiful nixie tube sits on a test rack, working through enough cycles to be certified ready for sale. The numbers crisp, clear, and beautiful. Great work keeping this loved part of history alive in the modern age.

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