Retrotechtacular: Circuit Potting, And PCBs The Hard Way

There was a time when the very idea of building a complex circuit with the intention of destroying it would have been anathema to any electrical engineer. The work put into designing a circuit, procuring the components, and assembling it, generally with point-to-point wiring and an extravagant amount of manual labor, only to blow it up? Heresy!

But, such are the demands of national defense, and as weapons morphed into “weapon systems” after World War II, the need arose for electronics that were not only cheap enough to blow up but also tough enough to survive the often rough ride before the final bang. The short film below, simply titled Potted and Printed Circuits, details the state of the art in miniaturization and modularization of electronics, circa 1952. It was produced by the Telecommunications Research Establishment (TRE), the main electronics R&D entity in the UK during the war which was responsible for inventions such as radar, radio navigation, and jamming technology.

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Homebrew Doorknob Caps For High-Voltage Fun

Mouser and Digi-Key are great for servicing most needs, and the range of parts they offer is frankly bewildering. But given the breadth of the hardware hacking community’s interests, few companies could afford to be the answer to everyone’s needs.

That’s especially true for the esoteric parts needed when one’s hobby involves high voltages and homemade lasers, like [Les Wright]. He recently came up with a DIY doorknob capacitor design that makes the hard-to-source high-voltage caps much easier to obtain. We’ve seen [Les] use these caps in his transversely excited atmospheric (TEA) lasers, a simple design that uses high-voltage discharge across a long, narrow channel filled with either room air or nitrogen. The big ceramic caps are needed for the HV supply, and while [Les] has a bunch, they’re hard to come by online. He tried a follow-up using plain radial-lead ceramic capacitors, and while the laser worked, he did get some flashover between the capacitor leads.

[Les]’s solution was to dunk the chunky caps in acetone for a week or so to remove their epoxy covering. Once denuded, the leads were bent into a more axial configuration and soldered to brass machine screws. The dielectric slug is then put in a small section of plastic tubing and potted in epoxy resin with the bolts protruding from each end. The result is hard to distinguish from a genuine doorknob cap; the video below shows the build process as well as some testing.

Hats off to [Les] for taking pity on those of us who want to replicate his work but find ourselves without these essentials. It’s nice to know there’s a way to make unobtanium parts when you need them.

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Designing And Building A Custom Optical Fuel Sensor

At some time or another, we’ve all had an idea we thought was so clever that we jumped on the Internet to see if somebody else had already come up with it. Most of the time, they have. But on the off chance that you can’t find any signs of it online, you’re left with basically two possible conclusions. Either you’re about to enter uncharted territory, or your idea is so bad that everyone has collectively dismissed it already.

Which is precisely where [James Stanley] recently found himself. He had an idea for an non-contact optical sensor which would detect when his racing mower was about to run out of gas by analyzing light passed through a clear section of fuel hose. He couldn’t find any previous DIY examples of such a device, nor did there appear to be a commercial version. But did that mean it wouldn’t work, or that nobody had ever tried before?

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He Comes To Bury Sensors, Not To Praise Them

[Adosia] has some interesting videos about their IoT platform controlling self-watering plant pots. However, the video that really caught our eye was the experience in sealing up sensors that are going to be out in the field. Even if you aren’t using the exact sensors, the techniques are useful.

We would have expected to see potting compound, but that’s messy and hard to use so their process is simpler. First, a few coats of clear urethane sealant goes over the electronics. Next, heat shrink goes over the assembly. It isn’t ordinary heat shrink though, instead it’s the kind that has heat-activated adhesive inside.

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Teardown: Refuel Propane Tank Monitor

Regular Hackaday readers will know that the clearance section of your local big box retailer is a great place to pick up oddball gadgets and gizmos for dirt cheap. In an era where manufacturers are rushing to make their products “smart” whether they need to be or not, the occasional ideas which fail to gain traction are just the cost of doing business. If you keep an eye out, you’re almost guaranteed to see one of these Internet of Things rejects collecting dust on a back aisle, often selling for pennies on the dollar.

Case in point, the “Refuel” propane tank monitor from Wink. Though there’s also logos for Quirky and GE on the package as well, and even a picture of the guy who came up with the idea. Essentially what we have here is a digital scale that reports the current weight of your grill’s propane tank to your phone via the Internet. A trick we might consider a fairly simple hack with a load cell and an ESP8266 under normal circumstances, but as this is a commercial product with an MSRP of $49.99 USD, its naturally been over-complicated to the point of absurdity.

Of course, one could simply lift the propane tank and get a decent estimate of its contents; a trick mastered by weekend grill masters since time immemorial. But then you wouldn’t have to make an account with Wink, or go through the very strange process of attempting to configure the device by using the flashing light of your smartphone’s screen (seriously). All so you can check how much propane is left in your grill while you’re away from home. You know, as one does.

Frankly, it’s hard for me to imagine who would actually have purchased such a thing at full retail. But of course, that’s likely why I was able to pick it up for the princely sum of $5. At that price, we can’t afford not to take a peek into this gizmo from Wink, Quirky, GE, and Anthony from Boston.

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Lessons In Disposable Design From A Cheap Blinky Ball

Planned obsolescence, as annoying as it is when you’re its victim, still has to be admired. You can’t help but stand in awe of the designer who somehow managed to optimize a product to live one day longer than its warranty period. Seriously, why is it always the next day?

The design of products that are never intended to live long enough to go obsolete must be similarly challenging, and [electronupdate] did a teardown of a cheap LED blinky toy to see what’s involved. You’ve no doubt seen these seizure-triggering silicone balls before, mostly at checkout counters and the like where they’re sold at prices many hundreds of times what it took to make them. This particular device, which seems representative of the species, has two bright LEDs, a small controller chip, a trio of button cells for power, and a springy switch to activate it. All this is mounted to a cheap scrap of phenolic resin PCB, with the controller chip and one of the LEDs covered by a blob of clear epoxy.

This teardown one-ups most others, as [electronupdate] disrobes the chip and points a microscope at the die; the video below shows just how few transistors are employed and proposes a likely circuit. Everything about this ball just oozes cheapness, and it’s likely these things cost essentially nothing to build. Which makes sense for something destined for the landfill within a week or so.

Yes, this annoying blinky-thing is low-end garbage, but there are still design lessons to be learned from it. Anything that’s built for a broad market has to be built to a price point, and understanding those constraints is important to understanding how planned obsolescence works.

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Repairing A Capacitor Inside A Potted Transformer

We always enjoy watching [Mr. Carlson’s] videos because he looks like he is taping in a rocket ship set from a 1950s drive-in movie. In a recent video, he identified an old oscilloscope that had a transformer assembly that is potted with a pair of capacitor inside. The capacitor failed so [Carlson] decided he would repair it. The problem? The transformer and capacitor are potted together with some sort of tar compound. You can see the result in the video below.

He actually didn’t know for sure the capacitor was really in the transformer, but they were in the schematic and by process of elimination, it had to be inside. Once he liberated the transformer, he did some tests to identify the capacitor before the depotting. The depotting takes a lot of heat and could damage the transformer, so he wanted to make sure it was really in there.

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