Sonoff Postmortem Finds Bugs, Literally

While nobody is exactly sure on the exact etymology of the term, Thomas Edison mentioned some of his inventions being riddled with “bugs” in a letter he wrote all the way back to 1878. In the context of computers, any loyal Hackaday reader should know Grace Hopper’s infamous account of a moth being caught in an early electromechanical computer’s relays. To this pantheon of troublesome insects, we would humbly summit the story of a Sonoff TH16 switch being destroyed by a lowly ant.

According to [CNX Software], the Sonoff TH16 had been working perfectly for a year and a half before the first signs of trouble. One day the switch wouldn’t respond to commands, and a power cycle didn’t seem to clear the issue. Upon opening up the device to see what had gone amiss, it was clearly apparent something had burned up. But upon closer inspection, it wasn’t a fault with the design or even a shoddy component. It was the product of an overly curious ant who got a lot more than he bargained for.

Consulting the wiring diagram of the Sonoff, it appears this poor ant had the terrible misfortune of touching the pins of a through hole capacitor on the opposite side of the board. Bridging this connection not only gave him a lethal jolt, but apparently caused enough current to surge through a nearby resistor that it went up in smoke.

Now, some might wonder (reasonably so) about the conditions in which this switch was operating. If bugs could climb into it, it’s not unreasonable to assume it wasn’t well protected from the elements. Perhaps damp conditions were to blame for the failure, and the image of the ant “riding the lighting” is nothing more than a coincidence. Maybe. But sometimes you just gotta believe.

Incidentally, if you’d like to learn more about the woman who helped secure “bugs” in the IT lexicon, here’s a good place to start.

Ed Note: If you think you’re having deja vu all over again, we did point to this story in the Sunday Links roundup, but the graphics are just so good we couldn’t resist running it in full.

Fail of the Week: Marginally Documented Pad Shorts to Maskless PCB

[Erich Styger] was bit by a nasty gotcha when soldering a QFN surface mount chip. The problem rears its ugly head when combining a chip possessing a padless conductor and a PCB without a solder mask. As you can see in the image above, there is a conductor exiting the side of the plastic QFN, but there is no pad associated with it. For this reason, you won’t see the conductor documented in the datasheet as a pin. It is documented in the mechanical drawing of the package, without any explicit reference to its existence. This is the Jason Bourne of package quirks.

The PCB layout just happens to have a trace exiting right under this conductor. The two aren’t touching, but without solder mask, a bit of melted metal was able to mind the gap and connect the two conductors. [Eric] notes that although the non-pad isn’t documented, it’s easy to prove that it is connected to ground and was effectively pulling down the signal on that trace.

In a recent article on Hackaday I talked about “dangling pointers” and the challenge when interrupts expose the bug. [Erich’s] covered a ton of posts about embedded software. I was doing some poking around and was delighted to find that he covered the same concept and a solution for it using a program called cppcheck.

Painting a wall with light using water as ink

This art installation uses a fantastic concept. The wall can be painted using water as ink which lights up a huge grid of white LEDs. This offers a very wide range of interactive possibilities since water can be applied in so many ways. Grab a paint brush, wet your finger, use a squirt gun, or mist with a spray bottle and the lights will tell you where you hit the wall.

We’re hoping a reader who speaks both French and English might help out by posting a translation as a comment on the prototyping video. In it, [Antonin Fourneau] shows off the various prototypes that led to the final product and we’d love to know what he’s saying. But by seeing the prototypes, then watching the English promo video after the break we can make a pretty good guess.  The boards have a hole that fits the flat-lens LEDs perfectly. This creates a mostly water tight seal to keep the liquid on one side while the leads are safe on the other. The water side has squiggly pads which allow droplets of water to complete an electrical connection.

Continue reading “Painting a wall with light using water as ink”

Making a smaller keyboard

The keyboard on [Marek’s] laptop stopped working. He didn’t want to buy a replacement so he decided to start using an external keyboard. But hauling around a full 104-key model is a bit of a pain so he decided to make himself a shorter keyboard. He basically chopped off the 10-key pad on the right side of the board. This had the unexpected consequence of removing the screws that hold the top and bottom of the case together so he ended up adding a few extra screws to shore it up. You may be wondering how the key matrix still works if a portion of it has been cut off. [Marek] used the simple trick of folding the extra part of the membrane over and covering the unused contacts with some tape.

If you try this you should consider getting rid of the directional arrows and editing keys as well. There must be a way to map those keys elsewhere. Perhaps the half-qwerty keyboard hack will give you some inspiration for that.