Fail Of The Week: Never Trust A Regulator Module

[Ryan Wamsley] has spent a lot of time over the past few months working on a new project, the Ultimate LoRa backplane. This is as its name suggests designed for LoRa wireless gateways, and packs in all the features he’d like to see in a LoRa expansion for the Nano Pi Duo.

His design features a three-terminal regulator, and in the quest for a bit more power efficiency he did what no doubt many of you will have done, and gave one of those little switching regulator modules in a three-terminal footprint a go. As part of his testing he inadvertently touched the regulator, and was instantly rewarded with a puff of smoke from his Nano Pi Duo. As it turned out, the regulator was susceptible to electrical noise, and had a fault condition in which its input voltage was routed directly to its output. As a result, a component in the single board computer received way more than its fair share, and burned out.

If there is a moral to be extracted from this story, it is to never fully trust a cheap drop-in module to behave exactly as its manufacturer claims. [Ryan]’s LoRa board lives to fight another day, but the smoke could so easily have come from more components.

So that’s the Fail of The Week part of this write-up complete, but it would be incomplete without the corresponding massive win that is [Ryan]’s LoRa board itself. Make sure to take a look at it, it’s a design into which a lot of attention to detail has been put.

A Lesson In K40 Laser Repair

The K40 laser cutter has become ubiquitous in hackerspaces and well-equipped home workshops over the past few years, as a relatively inexpensive introduction to laser cutting and a machine that is readily hackable. Tokyo Hackerspace have one, but sadly their laser tube failed after relatively little use. Replacing a laser tube might be a routine component change for some readers, but it’s still worth looking at in some detail.

Their tube had failed at its output lens cooling cap, a component that is glued onto the end of the tube rather than bonded, and which had snapped off. There had been no mechanical stress upon it, but it was foundĀ  that the arrangement of their cooling system caused it to drain between uses and thus air bubbles could accumulate. The resulting cooling inefficiency caused enough thermal stress for the bond between the tube and the end piece to fail.

The in-depth analysis of what caused the failure and step-by-step description of the procedure should be of interest to any K40 owner. Little things such as ensuring that the tube is rotated to the right angle for all air bubbles to make their way out of it, or making sure that when the pump is switched off the water isn’t all pulled out of it by gravity seem obvious, but these are traps that will have caught more than one K40 owner.

We’ve covered many K40 stories over the years, but a good place to start for the novice might be this commissioning story, or even this tale of a hackerspace’s modifications to their model.