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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Repairs You Can Print: Fixing a Rat-Attacked Mic Cord

We’ve all been there — a steamy night in the rainforest of Papua New Guinea, sweaty slumber disturbed by the unmistakable sounds of gnawing. In the morning we discover that a rodent of unusual tastes has chewed the microphone cable of our transceiver right half in two, leaving us out of touch with base camp. If we had a nickel for every time that’s happened.

It may sound improbable, but that’s the backstory behind [Marius Taciuc]’s 3D-printed mic cord repair. Even with more mundane failure modes, the retractile cords on microphones are notoriously difficult to fix. Pretty much any of the usual suspects, like heat-shrink tubing or electrical tape, are going to do very little to restore the mechanical stability lost once that tough outer jacket is breached. [Marius]’s solution was to print as small an enclosure as possible to mechanically support the splice. The fit is tight, but there was just enough room to solder the wires and stuff everything back in place. Cable ties provide strain relief where the cord exits the splice, and a liberal squirt of hot glue pots the joint. It’s not perfect — we’ll bet the splice acts as a catch point and gets a little annoying after a while — but if it gets you back on the air fast and cheap, it probably makes sense.

[Marius] entered this rat-race beating hack into the Repairs You Can Print contest. Do you have an epic repair that was made possible by a 3D printer? Let the world know about it and you might just win a prize.

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Exploring Options for DIY Waterproofing

TL;DR — Don’t use silicone to pot electronics.

That’s the conclusion [GreatScott!] comes to after trying out several methods for waterproofing electronics. His efforts stem from a recent video in which he discovered that water and electricity sometimes actually do mix, as long as the water is distilled and the electronics in the drink are relatively simple. He found that the main problem was, unsurprisingly, electrolytic corrosion, so he set out to experiment with various waterproofing coatings. In a series of careful experiments he goes through the pros and cons of both conformal coatings and potting compounds. The conformal tests used simple clear nail polish on an ESC board; that worked pretty well, but it was a little hard to reach all the nooks and crannies. He also tried potting with a thick black silicone compound, but that ended up never really curing in the middle. A final attempt with legitimate two-part epoxy potting compound sealed up the ESC tight, although we doubt the resulting brick would perform well on a quadcopter.

If you want to explore potting a bit further, check out this introduction to the basics.

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Conductive Concrete Confounds Circuitry

There’s a fairly good chance you’ve never tried to embed electronics into a chunk of concrete. Truth be told, before this one arrived to us via the tip line, the thought had never even occurred to us. After all, the conditions electronic components would have to endure during the pouring and curing process sound like a perfect storm of terrible: wet, alkaline, and with a bunch of pulverized minerals thrown in for good measure.

But as it turns out, the biggest issue with embedding electronics into concrete is something that most people aren’t even aware of: concrete is conductive. Not very conductive, mind you, but enough to cause problems. This is exactly where [Adam Kumpf] of Makefast Workshop found himself while working on a concrete enclosure for a color-changing barometer called LightNudge.

While putting a printed circuit board in the concrete was clearly not workable, [Adam] was hoping to simplify manufacturing of the device by embedding the DC power jack and capacitive touch sensor into the concrete itself. Unfortunately, [Adam] found that there was a resistance of about 200k Ohm between the touch sensor and the power jack; more than enough to mess with the sensitive measurements required for the touch sensor to function.

Even worse, the resistance of the concrete was found to change over time as the curing process continued, which can stretch out for weeks. With no reliable way to calibrate out the concrete’s internal conductivity, [Adam] needed a way to isolate his electronic components from the concrete itself.

Through trial and error, [Adam] eventually found a cheap method: dipping his sensor pad and wire into an acrylic enamel coating from the hardware store. It takes 24 hours to fully cure, and two coats to be sure no metal is exposed, but at least it’s an easy fix.

While the tip about concrete’s latent conductivity is interesting enough on its own, [Adam] also gives plenty of information about casting concrete parts which may be a useful bit of knowledge to store away for later. We have to admit, the final result is certainly much slicker than we would have expected.

This is the first one we’ve come across that’s embedded in concrete, but we’ve got no shortage of other capacitive touch projects if you’d like to get inspired.

A Short Introduction to Staking and Potting

Staking and potting are not often used in the hobby electronics world, not really entering to the common vernacular. However, everyone who’s ever busted out a glue-gun to convince that dang wire that keeps coming loose to stay has done it.

However, as [Sean Thomas] touches on, staking is not necessarily as easy as a dob of hot glue. There is a method to the madness. [Sean] gives some examples in pictures, but also directs people to the excellent NASA standard methods for staking. It’s surprising how many unintuitive caveats there are to the proper technique.

Potting, or covering everything in epoxy forever, is a great way to get a waterproof, unserviceable, and practically mechanically invincible circuit. The big challenge in potting is picking the right material. A soft silicone, for example, might transfer an unexpected force to an unexpected section of the circuit and cause a mechanical failure. A nice hard epoxy may be too insulating and cause a thermal failure. The standard RTV from the big box store has acetic acid that will eat your components.

These two techniques that come in handy when you need them and worth the bit of reading it takes to get familiar. Have you used either in your own workshop? Let us know the application and the material/techniques you have tried in the comments below.

Tint your Epoxy Resin with Toner Powder

Epoxy resin is useful stuff. Whether for gluing stuff together or potting components, epoxy is a cheap and versatile polymer that finds its way into many hackish projects. But let’s face it – the stock color of most commercially available epoxies lacks a certain pizzazz. Luckily, [Rupert Hirst] at Tallman Labs shows us that epoxy is easily tinted with toner powder from a laser printer or copier.

Looking for a way to make his epoxy blend into a glue-up, [Rupert] also demonstrates that colored epoxy makes a professional looking potting compound. There’s just something about the silky, liquid look of a blob of cured black epoxy. [Rupert] harvested his toner powder from a depleted printer cartridge; only a smidgen is needed, so you should be able to recover plenty before recycling the cartridge. We’ve got to admit that seeing toner handled without gloves gives us the willies, though. And don’t forget that you can find cyan, magenta and yellow cartridges too if basic black isn’t your thing.

Sometimes it’s better to leave your epoxy somewhat clear, like when you’re potting an LED matrix for a pendant. But this neat trick might just spiff up your next project a bit.

[Thanks, Jake]