Have you heard it said that everything in Linux is a file? That is largely true, and that’s why the ability to manipulate files is crucial to mastering Linux Fu.
One thing that makes a Linux filesystem so versatile is the ability for a file to be many places at once. It boils down to keeping the file in one place but using it in another. This is handy to keep disk access snappy, to modify a running system, or merely to keep things organized in a way that suits your needs.
There are several key features that lend to this versatility: links, bind mounts, and user space file systems immediately come to mind. Let’s take a look at how these work and how you’ll often see them used.
Last time, we covered storing and charging a 3000 Farad supercapacitor to build a solar-powered, portable spot welder. Since then, I’ve made some improvements to the charging circuit and gotten it running. To recap, the charger uses a DC-DC buck converter to convert a range of DC voltages down to 2.6 V. It can supply a maximum of 5 A though, and the supercapacitor will draw more than that if allowed to.
Capacitor charge current decreases with time as the capacitor charges. Source: Hyperphysics
After some failed attempts, I had solved that by passing the buck converter output through a salvaged power MOSFET. A spare NodeMCU module provided pulse width modulated output that switched the MOSFET on for controlled periods of time to limit the charging current. That was fine, but a constant-voltage charger really isn’t the right way to load up a capacitor. Because the capacitor plates build up a voltage as it charges, the current output from a constant-voltage charger is high initially, but drops to a very low rate in the end.
Today is March 14th, or Pi Day because 3.14 is March 14th rendered in month.day date format. A very slightly better way to celebrate the ratio of a circle’s circumference to its diameter is July 22nd, or 22/7 written in day/month order, a fractional approximation of pi that’s been used for thousands of years and is a better fit than 3.14. Celebrating Pi Day on July 22nd also has the advantage of eschewing middle-endian date formatting.
But Pi Day is completely wrong. We should be celebrating Tau Day, to celebrate the ratio of the circumference to the radius instead of the diameter. That’s June 28th, or 6.283185…. Nonetheless, today is Pi Day and in the absence of something truly new and insightful — we’re still waiting for someone to implement a spigot algorithm in 6502 assembly, by the way — this is a fantastic opportunity to discuss something tangentially related to pi, the history of mathematics, and the idea that human knowledge builds upon itself in an immense genealogy stretching back to the beginning of history.
This is our Pi Day article, but instead of complaining about date formats, or Tau, we’re going to do something different. This is how you approximate pi with the Monte Carlo method, and how anyone who can count to a million can get a better approximation of one the fundamental constants of the Universe than Archimedes.
While the Raspberry Pi’s birthday (and the traditional release date for the newest and best Pi) was a few weeks ago, Pi Day is a fitting enough date for the introduction of the best Pi to date. The Raspberry Pi 3 Model B+ is the latest from the Raspberry Pi foundation. It’s faster, it has better networking, and most interestingly, the Pi 3 Model B+ comes with modular compliance certification, allowing anyone to put the Pi into a product with vastly reduced compliance testing.
It’s fair to say that software-defined radio represents the most significant advance in affordable radio equipment that we have seen over the last decade or so. Moving signal processing from purpose-built analogue hardware into the realm of software has opened up so many exciting possibilities in terms of what can be done both with more traditional modes of radio communication and with newer ones made possible only by the new technology.
It’s also fair to say that radio enthusiasts seeking a high-performance SDR would also have to be prepared with a hefty bank balance, as some of the components required to deliver software defined radios have been rather expensive. Thus the budget end of the market has been the preserve of radios using the limited baseband bandwidth of an existing analogue interface such as a computer sound card, or of happy accidents in driver hacking such as the discovery that the cheap and now-ubiquitous RTL2832 chipset digital TV receivers could function as an SDR receiver. Transmitting has been, and still is, more expensive.
The LimeSDR Mini’s chunky USB stick form factor.
A new generation of budget SDRs, as typified by today’s subject the LimeSDR Mini, have brought down the price of transmitting. This is the latest addition to the LimeSDR range of products, an SDR transceiver and FPGA development board in a USB stick format that uses the same Lime Microsystems LMS7002M at its heart as the existing LimeSDR USB, but with a lower specification. Chief among the changes are that there is only one receive and one transmit channel to the USB’s two each, the bandwidth of 30.72 MHz is halved, and the lower-end frequency range jumps from 100 kHz to 10 MHz. The most interesting lower figure associated with the Mini though is its price, with the early birds snapping it up for $99 — half that of its predecessor. (It’s now available on Kickstarter for $139.)
Today the 2018 Hackaday Prize begins with a roar. This is our global engineering initiative with huge prizes for those hackers, designers, and engineers who want to use their skill and energy to build something that matters. This year, we challenge you to Build Hope. Show the world the amazing ways technology enriches humanity, and that its benefits can be shared by all.
There is over $200,000 in cash prizes headed to the most interesting hardware builds of the year. With plenty of room for great ideas, the top 100 entries will each receive a $1,000 cash prize and continue the build to final judging. The top five entries will be awarded a $50,000 Grand Prize, and $20,000, $15,000, $10,000, and $5,000 for 2nd through 5th places. We even have some additional seed funding set aside to help early entries to get started.
What is Building Hope?
It feels like there is a steady drumbeat of doom and gloom surrounding technology these days. We hear this foretold in many ways, things like robots rising up to enslave humanity, artificial intelligence and big data being used to manipulate people, and quantum computing on the horizon that will invalidate cryptographic security. Our challenge? Get in there and show the incredible good that technology can do in the world.
Design something that shows the benefits of using knowledge and creativity to solve a problem. Be the shining light that proves our future is full of hope because smart people care about what happens in the world and to the people who live here. It is our responsibility as those who understand powerful technologies to show the best ways they can be used to build up humanity. This is your chance.
We have five challenge categories to choose from in the 2018 Hackaday Prize. The top twenty entries from each category will receive $1,000 and continue work in order to compete for the top prizes.
Open Hardware Design Challenge:
This is the challenge you should enter right now. Choose a challenge facing the world today and design the best plan possible for the boldest solution you can envision.
Over the years we’ve seen thousands of Hackaday Prize entries that take on farming, transportation, pollution, safety, scientific research, education, and assistive technologies like custom prosthetics, innovative wheelchairs, and braille interfaces for smartphones. There’s plenty in the world that needs solving and you have the talent to do it!
Robotics Module Challenge:
Build a module that makes it easier to put together advanced robots. Show your designs for the parts that others can build on.
Power Harvesting Challenge:
Build a module that harvests ambient power. Show how we can reduce or remove batteries from more devices.
Human Computer Interface Challenge:
Build an innovative interface for humans to talk to machines or machines to talk to humans. Break down more barriers to make devices more intuitive and natural to use.
Musical Instrument Challenge:
Be creative with this round and build a module, interface, or full instrument that evolves or goes far beyond modern music instrumentation.
Seed Funding For Early Entries
Itching to build something? Get a boost on your material budget by securing a bit of seed funding. Enter your design in the first challenge and pack it with as much information as possible. Each “like” that you get from the Hackaday.io community translates to $1 in seed funding. We have $4000 set aside with a max of $200 per entry. You can follow progress by checking the leaderboard on the Hackaday Prize page.
Incredible Judges
The Hackaday Prize has something really special in the judges that volunteer their time and talent to review the 100 finalists. They are accomplished engineers working, researching, and forging ahead to new frontiers in technology. Learn more about the judges on the Hackaday Prize page.
Get Started at World Create Day
This coming Saturday is Hackaday World Create Day, and the perfect time to get started with your Hackaday Prize entry. Stop by a meetup in your area (or host your own) and put your heads together and pick the design challenge you want to work on. We love seeing collaborative entries and this is a great chance to build your engineering dream team.
Five Years of Amazing Engineering
Thousands of entries have been submitted to the Hackaday Prize over the years. Founded in 2014 by Supplyframe CEO Steve Flagg, the Hackaday Prize is now in its fifth year. The challenges change each year, but the goal remains the same: to Build Something That Matters. We are consistently amazed both by the quality of the solutions, and the uncovering of new and interesting problems targeted by the entries.
Studying earth’s oceans is increasingly important be it due to climate change or pollution. Alex Williams was awarded the 2017 Hackaday Prize for his Open Source Underwater Glider, a suite of sensors built into a cleverly low-power underwater autonomous vehicle. In 2016, Alberto Molina took the top spot for DTTO, a modular robotics system made up of multiple single-hinge segments that can reorient themselves. A team working toward an eye-controlled electric wheelchair placed first in 2015 for Eyedriveomatic — a solution that improved life for two of the team members with Motor Neuron Disease, (also called ALS). And the recipients of the first Hackaday Prize were recognized for their team’s development of a network of satellite ground stations (SatNOGS) which anyone can build, add to the network, and share time on to communicate with satellites as they make their orbit. This is an important tool to make low-cost research for things like Cubesats possible, and the network has been growing ever since.
If you feel the need for more inspiration, take a few minutes to look over the Hackaday Prize hall of fame of all of the top finishers through the years.
These are impressive ideas that began with the basic question of how can we do better? A simple idea can change the world but only if you share that idea and work to make it grow. Enter yours in the Hackaday Prize now!
Audacious times generate audacious efforts, especially when national pride and security are perceived to be at stake. Such was the case in the 1950s and 1960s, with the Space Race that started with a Russian sphere whizzing around the planet and ended with Neil Armstrong’s footprint on the Moon. But at the same time, other efforts were underway to answer big questions of national import, such as determining how durable the United States’ strategic assets were, and whether they could withstand the known effects of electromagnetic pulse (EMP), a high-intensity burst of electromagnetic energy that could potentially disable a plane in flight. Finding out just what an EMP could do to a plane would take big engineering and a large forest’s worth of trees.
Studying earth’s oceans is increasingly important be it due to climate change or pollution. Alex Williams was awarded the 2017 Hackaday Prize for his 
