Many of us have experienced the pain that is a Raspberry Pi with a corrupted SD card. I suspect the erase-on-write nature of flash memory is responsible for much of the problem. Regardless of the cause, one solution is to use PXE booting with the Raspberry Pi 3. That’s a fancy way to say we’ll be booting the Raspberry Pi over the network, instead of from an SD card.
What does this have to do with Hacking My House? As I discussed last time, I’m using Raspberry Pi as Infrastructure by building them into the walls of every room in my house. You don’t want to drag out a ladder and screwdriver to swap out a misbehaving SD card, so booting over the network is a really good solution. I know I promised we’d discuss cabling and cameras. Think of this as a parenthetical article — we’ll talk about Ethernet and ZoneMinder next time.
So let’s dive in and see what the Preboot Execution Environment (PXE) is all about and how to use PXE with Raspberry Pi.
Come one, come all, this is the megapost about the Hackaday Superconference. Join us in Pasadena on November 2-4 for the hardware conference you cannot miss. Get your ticket quickly as they will sell out!
Soon, perhaps even by the time you read this, the rules for flying remote-controlled aircraft in the United States will be very different. The Federal Aviation Authority (FAA) is pushing hard to repeal Section 336, which states that small remote-controlled aircraft as used for hobby and educational purposes aren’t under FAA jurisdiction. Despite assurances that the FAA will work towards implementing waivers for hobbyists, critics worry that in the worst case the repeal of Section 336 might mean that remote control pilots and their craft may be held to the same standards as their human-carrying counterparts.
Section 336 has already been used to shoot down the FAA’s ill-conceived attempt to get RC pilots to register themselves and their craft, so it’s little surprise they’re eager to get rid of it. But they aren’t alone. The Commercial Drone Alliance, a non-profit association dedicated to supporting enterprise use of Unmanned Aerial Systems (UAS), expressed their support for repealing Section 336 in a June press release:
Basic ‘rules of the road’ are needed to manage all this new air traffic. That is why the Commercial Drone Alliance is today calling on Congress to repeal Section 336 of the FAA Modernization and Reform Act of 2012, and include new language in the 2018 FAA Reauthorization Act to enable the FAA to regulate UAS and the National Airspace in a common sense way.
With both the industry and the FAA both pushing lawmakers to revamp the rules governing small remote-controlled aircraft, things aren’t looking good for the hobbyists who operate them. It seems likely those among us with a penchant for airborne hacking will be forced to fall in line. But what happens then?
After exploring a few random online shops one day, [David] (thanks for sending this in, by the way) ran across a very interesting chip. It’s a dual-core, RISC-V chip running at 400MHz. There’s 6 MB of SRAM on the CPU, and there’s 2MB for convolutional neural network acceleration. There is, apparently, WiFi on some versions. There are already SDKs available on GitHub, and a bare chip costs a dollar or two. Interested? Log in to Taobao, realize Taobao does pre-orders, and all this can be yours.
This is a preorder — because apparently you can do that as a seller on TaoBao, but the Sipeed M1 K210 is available as a ‘core’ board with 72 pins in a one-inch square package, a version with WiFi, or as a complete development board with an OV2640 camera, 2.4 inch LCD, microphone, and onboard USB. There are videos of this chip running a face detection routine. It found Obama.
Over the years we’ve seen a few RISC-V chips given development boards, and you can buy them right now. The HiFive 1 is an exceptionally powerful microcontroller with processing power that puts it right up against the Teensy (which is built around a Freescale chip), but it’s also fairly expensive. We’re not sure the Arduino Cinque (also RISC-V) ever made it to production, but again, expensive. The idea that a RISC-V microcontroller could be available for just a few dollars is very interesting, it even comes with SDKs and utilities to make the chip useful.
It is good advice to change batteries in your fire alarms at least once a year. Even our low-power LCD calculators need new batteries from time to time. But at the University of Oxford, they have an electric bell that has been ringing essentially non-stop on one set of batteries for about 178 years! Is the energy crisis solved then? Perhaps not. The bells require a high voltage but very little current and the pair of batteries — piles in the parlance of 1840 — have kept the charge flowing for about 10 billion rings. As you can see in the video below, though, the ringing isn’t very vigorous.
How does it work? When you think of converting electrical power to mechanical motion you probably think of a motor, even though there are plenty of other transducers like speakers, muscle wires, and solenoids. Arguably the first device was electrostatic bells that were invented by a Scot named [Andrew Gordon] around 1742. [Ben Franklin] made them famous, though, so they are often called Franklin bells.
Nearly a decade ago my friend [Dru] gave me an unforgettable tour late at night of Stokes Croft, the inner suburb of Bristol known at the time for its counterculture and artistic scene. It’s a place dominated by building-sized graffiti and murals, and it has a particular association with the Bristolian street artist [Banksy]. If you’ve not seen a Banksy in the wild, the place to do it is by Bristol Saturday night street lighting to the sound of passing revelers and traffic on the A38.
[Banksy] is famous aside from his anonymity, for his pranks upon the art world. The (real) elephant in the room or the Dismalland theme park are his stock in trade, and you may have seen another prank of his in the news in the last day. One of his paintings, the 2006 Girl With A Balloon sold at auction for over a million quid, and as the gavel fell a hidden shredder in the picture frame sprang into life and partially shredded the canvas. The report suggests that a number of [Banksy]’s associates were present at the event, and that one of them was detained with a device that might have been a remote control trigger for the shredder. The quote from Sotheby’s Europe head of Contemporary Art, [Alex Branczik] says it all: “We got Banksy’d”.
The interior of the Banksy shredder frame, taken from a frame of the video.
[Banksy]’s cool and all that, but where’s the hack? The artist briefly put up a video with a few details, but aside from showing us a row of craft knife blades and a tantalizing but fleeting glimpse of a few equipment enclosures, it’s short on technical details. We can see what appears to be at least one motor, and those white boxes may be batteries, but that’s it.
This hasn’t stopped some fevered speculation as to how the feat was achieved. A home-made shredder would require a significant amount of readily available power, and since this one has seemingly lain undetected within the frame since 2006, that power source needs to have possessed both exceptional energy density and retention. We can’t imagine many consumer grade batteries in 2018 being able to retain a charge for twelve years, so how on earth did he do it? Our best guess is that a primary battery was involved, as anyone who has found a neglected Duracell in a box of electronics from their youth will tell you it’s not unknown for decent quality alkaline cells to live well beyond their shelf lives, and other chemistries are specifically designed with that property in mind. Even so, for the cells to power a receiver circuit in standby for so long would certainly tax their capabilities, so it has also been suggested that a concealed switch could have been flipped by a [Banksy] accomplice during the viewing phase to activate the system. There are still so many unanswered questions that it’s certainly piqued our technical curiosity. Sadly we don’t know [Banksy] to ask him how he did it, but we welcome speculation both informed and otherwise in the comments.
Our own [Joe Kim]’s tribute to the work in question.Meanwhile the piece itself lies half shredded and protruding from the base of the frame. On the face of it that’s ruined the painting as an artwork, but of course this is a Banksy. Normal rules seem not to apply, so the notoriety it has received will no doubt mean that its shredded remains are an artwork in themselves, and possibly even one worth more.
Banksy owners worldwide are no doubt now paying a huge amount more attention to the artist’s frames than previously, but Hackaday readers need not worry. Our London Unconference logo and stickers featured a [Joe Kim] homage to the Banksy in question, which we can guarantee does not incorporate an artist’s shredder.
How does a design go from the computer screen to something you hold in your hand? Not being able to fully answer this question is a huge risk in manufacturing because . One of the important tools engineers use to ensure success is Geometric Dimensioning and Tolerancing (GD&T).
A good technical drawing is essential for communicating your mechanical part designs to a manufacturer. Drafting, as a professional discipline, is all about creating technical drawings that are as unambiguous as possible, and that means defining features explicitly. The most basic implementation of that concept is dimensioning, where you state the distance or angle between features. A proper technical drawing will also include tolerances for those dimensions, and I recently explained how to avoid the pitfall of stacking those tolerances.
Dimensions and tolerances alone, however, don’t tell the complete story. On their own, they don’t specify how closely the geometric form of the manufactured part needs to adhere to your perfect, nominal representation. That’s what we’re going to dig into today with GD&T.
![Our own [Joe Kim]'s tribute to the work in question.](https://hackaday.com/wp-content/uploads/2017/07/london.jpg)
