Fail Of The Week: The Pitfalls Of Designing A Wideband Radio

If you are someone whose interests lie in the field of RF, you won’t need telling about the endless field of new possibilities opened up by the advent of affordable software defined radio technology. If you are a designer or constructor it might be tempting to believe that these radios could reduce some of the problems facing an RF design engineer. After all, that tricky signal processing work has been moved into code, so the RF engineer’s only remaining job should be to fill the not-so-huge gap between antenna and ADC or DAC.

In some cases this is true. If you are designing an SDR front end for a relatively narrow band of frequencies, perhaps a single frequency allocation such as an amateur band, the challenges are largely the same as those you’d find in the front end of a traditional radio. The simplest SDRs are thus well within the abilities of a home constructor, for example converting a below-100kHz-wide segment of radio spectrum to the below-100kHz baseband audio bandwidth of a decent quality computer sound card which serves as both ADC and DAC. You will only need to design one set of not-very-wide filters, and the integrated circuits you’ll use will not be particularly exotic.

But what happens if the SDR you are designing is not a simple narrow-band device? [Chris Testa, KD2BMH] delivered a talk at this year’s Dayton Hamvention looking at some of the mistakes he made and pitfalls he encountered over the last few years of work on his 50MHz to 1GHz-bandwidth Whitebox handheld SDR project. It’s not a FoTW in the traditional sense in that it is not a single ignominious fail, instead it is a candid and fascinating examination of so many of the wrong turnings a would-be RF engineer can make.

The video of his talk can be found below the break, courtesy of Ham Radio Now. [Chris]’s talk is part of a longer presentation after [Bruce Perens, K6BP] who some of you may recognise from his activities when he’s not talking about digital voice and SDRs. We’re jumping in at about the 34 minute mark to catch [Chris], but [Bruce]’s talk is almost worth an article in itself..

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Fail of the Week: Magnetic Flow Measurement Gone Wrong

Physics gives us the basic tools needed to understand the universe, but turning theory into something useful is how engineers make their living. Pushing on that boundary is the subject of this week’s Fail of the Week, wherein we follow the travails of making a working magnetic flowmeter (YouTube, embedded below).

Theory suggests that measuring fluid flow should be simple. After all, sticking a magnetic paddle wheel into a fluid stream and counting pulses with a reed switch or Hall sensor is pretty straightforward, right? In this case, though, [Grady] of Practical Engineering starts out with a much more complicated flow measurement modality – electromagnetic detection. He does a great job of explaining Faraday’s Law of Induction and how a fluid can be the conductor that moves through a magnetic field and has a measurable current induced in it. The current should be proportional to the velocity of the fluid, so it should be a snap to whip up a homebrew magnetic flowmeter, right? Nope – despite valiant effort, [Grady] was never able to get a usable signal out of the noise in his system. 

The theory is sound, his test rig looks workable, and he’s got some pretty decent instrumentation. So where did [Grady] go wrong? Could he clean up the signal with a better instrumentation amp? What would happen if he changed the process fluid to something more conductive, like salt water? By his own admission, electrical engineering is not his strong suit – he’s a civil engineer by trade. Think you can clean up that signal? Let us know in the comments section. 

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Fail of the Week: Ferrofluid

It’s more of a half-fail than a full fail, but [Basti] is accustomed to getting things right (eventually) so it sticks in his craw that he wasn’t able to fully realize his ferrofluid dreams (German, translated here). Anyway, fail or demi-fail, the project is certainly a lesson in the reality of ferrofluid.

ferro

We’ve all seen amazing things done with ferrofluid and magnets. How hard can it be to make an interactive ferrofluid wedding present for his sister? Where ferrofluid spikes climb up a beautifully cut steel heart in a jar? (Answer: very hard.)

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Fail Of The Week: How Not To Build Your Own Motorcycle

There’s a saying among writers that goes something like “Everyone has a novel in them, but in most cases that’s where it should stay”. Its source is the subject of some dispute, but it remains sage advice that wannabe authors should remember on dark and stormy nights.

It is possible that a similar saying could be constructed among hackers and makers: that every one of us has at least one motor vehicle within, held back only by the lack of available time, budget, and workshop space. And like the writers, within is probably where most of them should stay.

[TheFrostyman] might have had cause to heed such advice. For blessed with a workshop, a hundred dollars, and the free time of a 15-year-old, he’s built his first motorcycle. It’s a machine of which he seems inordinately proud, a hardtail with a stance somewhere closer to a café racer and powered by what looks like a clone of the ubiquitous Honda 50 engine.

Unfortunately for him, though the machine looks about as cool a ride as any 15-year-old could hope to own it could also serve as a textbook example of how not to build a safe motorcycle. In fact, we’d go further than that, it’s a deathtrap that we hope he takes a second look at and never ever rides. It’s worth running through some of its deficiencies not for a laugh at his expense but to gain some understanding of motorcycle design.

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Fail Of The Week (in 1996): The 7 Billion Dollar Overflow

The year was 1996, the European Space agency was poised for commercial supremacy in space. Their new Ariane 5 Rocket could launch two three-ton satellites into space. It had more power than anything that had come before.

The rocket rose up towards the heavens on a pillar of flame, carrying four very expensive and very uninsured satellites. Thirty-seven seconds later it self destructed. Seven billion dollars of RUD rained down on the local beaches near the Guiana Space Centre in Southern South America. A video of the failed launch is after the break.

The cause of all this was a single improper type cast in a bit of code that wasn’t even supposed to run during the actual launch. Talk about a fail.

There were two bits of code. One that measured the sideways velocity, and one that used it in the guidance system. The measurement side used a 64 bit variable, but the guidance side used a 16 bit variable. The code was borrowed from an earlier, slower rocket whose velocity would never grow large enough to exceed that 16 bits. The Ariane 5, however, could be described with a Daft Punk song, and quickly overflowed this value.

The code that caused the overflow was actually a bit of pre-launch software that aligned the rocket. It was supposed to be turned off before the rocket firing, but since the rocket launch got delayed so often, the engineers made it timeout 40 seconds into the launch so they didn’t have to keep restarting it.

The ESA never placed blame on a single contractor. The programmers had made assumptions. The engineers had made reasonable shortcuts to make their job easier. It had all made it through inspections, approvals, and finally the launch event.

They certainly learned from the event; the Ariane 5 rocket has flown 82 out of 86 missions successfully since then. It has at least five more launches contracted before it is retired in 2023 for the Ariane 6 rocket being developed now. This event also changed the way critical software and redundant systems were tested, bringing the dangers of code failure to the attention of the public for the first time.

If you want to read more, there is a great discussion on Reddit which tipped us off to this fail, a quite thorough Wikipedia article, and the original article that ran in the New York Times is mirrored here.

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Fail of the Week: Arachno∙fail∙ia

Going down the list (FCC, CE, UL, etc.) we can’t think of a regulating body that will test for this failure mode. Reportedly, a $1M irrigation system was taken down by a spider. And an itsy-bitsy spider at that.

This fail turned up as a quick image post over on /r/mildlyinteresting but I wasn’t the only electronics person attracted like a moth to a flame. Our friend [Sprite_TM] popped in to answer a question about conformal coating. Seems this board was sealed in a waterproof enclosure but was obviously not conformally coated.

fotw-spider-short-relay-diagram[Sprite_TM] also helped out with some armchair-engineering to guess at what happened. It’s not hard to tell that the footprint on the board looks like a set of mechanical relays all in a line. He looked up the most likely pinout for the relay.

We’ve superimposed that pinout on the board to help illustrate the failure. High voltage comes in on the pin shown with the red trace leading away from it. On either side of that pin are the connections for the low voltage coil which switches from normally closed (the pin in the upper right that is not connected to anything) to the normally open pin (which has the wide trace leading away from it).

So there sat the high voltage pin in between the coil pins when, along came a spider. It shorted the pins and presumably all the way back to the power supply for the low voltage rail. [Fugly_Turnip] (the OP) share some additional detail about the system and this failure; in addition to this card it fried the control module as well.

Another comment on the same thread shares a different story of two boards mounted next to each other with a bug shorting a 1/4″ air gap between two boards and causing similar carnage. Have you encountered Arachno-fail-ia of your own? Let us know below.


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.

Fail Of The Week: Where’s Me Jumper?

Just in case you imagine that those of us who write for Hackaday are among the elite of engineering talent who never put a foot wrong and whose benches see a succession of perfectly executed builds and amazing hacks, let me disabuse you of that notion with an ignominious failure of my own.

I was building an electronic kit, a few weeks ago. It’s a modular design with multiple cards on a backplane, though since in due course you’ll see a review of it here I’ll save you its details until that moment. In my several decades of electronic endeavours I have built many kits, so this one as a through-hole design on the standard 0.1″ pitch should have presented me with no issues at all. Sadly though it didn’t work out that way.

Things started to go wrong towards the end of the build, I noticed that the temperature regulator on my soldering iron had failed at some point during its construction. Most of it had thus been soldered at a worryingly high temperature, so I was faced with a lot of solder joints to go over and rework in case any of them had been rendered dry by the excessive heat.

In due course when I powered my completed kit up, nothing worked. It must have been the extra heat, I thought, so out came the desolder braid and yet again I reworked the whole kit. Still no joy. Firing up my oscilloscope I could see things happening on its clock and data lines so there was hope, but this wasn’t a kit that was responding to therapy. A long conversation with the (very patient) kit manufacturer left me having followed up a selection of avenues, all to no avail. By this time a couple of weeks of on-and-off diagnostics had come and gone, and I was getting desperate. Somehow I’d cooked this thing with my faulty iron, and there was no way to find the culprit.

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