Tripping Out: A Field Guide To Circuit Protection

My introduction to circuit protection came at the tender age of eight. Being a curious lad with an inventive – and apparently self-destructive – bent, I decided to make my mother a lamp. I put a hose clamp around the base of a small light bulb, stripped the insulation off an old extension cord, and jammed both ends of the wires under the clamp. When I plugged my invention into an outlet in the den, I saw the insulation flash off the cord just before the whole house went dark. Somehow the circuit breaker on the branch circuit failed and I tripped the main breaker on a 200 amp panel. My mother has never been anywhere near as impressed with this feat as I was, especially now that I know a little bit more about how electricity works and how close to I came to being a Darwin Award laureate.

To help you avoid a similar fate, I’d like to take you on a trip (tee-hee!) through the typical household power panel and look at some of the devices that stand at the ready every day, waiting for a chance to save us from ourselves. As a North American, I’ll be focusing on the residential power system standards most common around here. And although there is a lot of technology that’s designed to keep you safe as a last resort, the electricity in your wall can still kill you. Don’t become casual with mains current!

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A Win For The Raspberry Pi Compute Module

News comes from the Raspberry Pi Foundation, of something of a coup for their Compute Module product. Support for it is to be integrated into NEC’s line of commercial displays, and the electronics giant has lined up a list of software partners to provide integrated signage solutions for the platform.

It is interesting to note how NEC have done this, while it’s being spun by the Foundation as a coup for them the compute module sits on a daughter board in a slot on the back of the display rather than on the display PCB itself. They are likely hedging their bets with this move, future daughter boards could be created to provide support for other platforms should the Compute Module board fail to gain traction.

Given that this relates to a high-end commercial product from just one manufacturer, what’s in it for us in the hardware community? After all, it’s not as if you’ll be seeing Compute Module slots in the back of domestic TVs or monitors from NEC or any other manufacturer in the near future. The answer is that such a high-profile customer lends the module platform a commercial credibility that it may not yet have achieved.  Until now, it has found a home mainly in more niche or boutique products, this appearance in something from a global manufacturer takes it to a new level. And as the module finds its way into more devices the chances of them coming within the reach of our community and providing us with opportunities for adapting them for our purposes through the Pi platform become ever greater.

The use of the Compute Module in displays made for public signage is oddly a continuation of an unseen tradition for ARM-based machines from Cambridge. Aside from British schools a significant market for the Acorn Archimedes platform that spawned ARM was the embedded signage market, and even today there are still plenty of signs concealing RiscOS machines out there in the wild.

We covered the launch of the Compute Module in 2014, but it’s fair to say it’s not appeared much since in the world of Raspberry Pi projects from hardware hackers. This is not because it’s not a good platform; more likely that the Raspberry Pi models A, B, and particularly the Zero are so much cheaper when you consider the significant cost of the Compute Module development board. At the Raspberry Pi 4th birthday party earlier this year, while covering the event as your Hackaday scribe but also wearing my metaphorical Pi kit supplier and Pi Jam organizer hats I stood up in the Q&A session and asked the Foundation CEO Phil Colligan to consider a hardware developer program for the platform. Perhaps a cut-down Compute Module developer board would be an asset to such a program, as well as driving more adoption of that particular board.

Scissors Make Great Automatic Cable Cutters

The team at [2PrintBeta] required a bunch of cables, heat shrink, and braid to be cut for their customers. They looked into an industrial cable cutter, but decided the price was a little too high, so they decided to make their own. They had a bunch of ideas for cutting: Using a razor blade?  Or a Dremel with a cutting wheel? What they came up with was a DIY cable cutter that uses a pair of scissors, a pair of stepper motors, a pair of 3D printed wheels and an Arduino.

The first thing the team had to do was to mount the scissors so they would cut reliably. One of the stepper motors was attached to a drive wheel that had a bolt mounted on it. This went through one of the scissors’ handles, the other handle was held in place on the machine using screws. The second stepper motor was used to rotate the wheels that drives the cable through to the correct length. [2PrintBeta] used a BAM&DICE shield and two DICE-STK stepper motor drivers on an Arduino Mega to control the cutter.

The [2PrintBeta] team are pretty good at doing things themselves, as we’ve seen previously with their DIY plastic bender. And again, with this automatic cable cutter, they’ve seen a need and resolved it using the things at their disposal and some DIY ingenuity.

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