It is easy to dismiss bash — the typical Linux shell program — as just a command prompt that allows scripting. Bash, however, is a full-blown programming language. I wouldn’t presume to tell you that it is as fast as a compiled C program, but that’s not why it exists. While a lot of people use shell scripts as an analog to a batch file in MSDOS, it can do so much more than that. Contrary to what you might think after a casual glance, it is entirely possible to write scripts that are reliable and robust enough to use in many embedded systems on a Raspberry Pi or similar computer.
I say that because sometimes bash gets a bad reputation. For one thing, it emphasizes ease-of-use. So while it has features that can promote making a robust script, you have to know to turn those features on. Another issue is that a lot of the functionality you’ll use in writing a bash script doesn’t come from bash, it comes from Linux commands (or whatever environment you are using; I’m going to assume some Linux distribution). If those programs do bad things, that isn’t a problem specific to bash.
One other limiting issue to bash is that many people (and I’m one of them) tend to write scripts using constructs that are compatible with older shells. Often times bash can do things better or neater, but we still use the older ways. For example:
Hackaday is all over this eclipse. There are thousands of members of the Hackaday community headed to a narrow swath of the United States on August 21st to revel in an incredibly rare, scientifically predictable life experience: a total eclipse of the sun.
Do not do it in solitude, get together and celebrate! Check out the Hackaday Eclipse Meetups page which shows where meetups are happening. And adding your own is simple. It’s a great day to meet up with other Hackaday readers and celebrate the day that the moon passed perfectly between you and the sun.
You can’t just stare directly at the sun, you need some eclipse glasses. We’re printing up some in black, adorned with the Jolly Wrencher and sending them out to all organized meetups, so get your event page up today and you’re on the list for a little bit of sweet swag. Look for the button on the Eclipse page that says “Host a meetup”.
I’m Too Cool to Watch an Eclipse
If you don’t get what all the hubbub is, you’re missing out. A total eclipse of the sun is an amazing life experience in so many ways. First off, they’re incredibly rare. There hasn’t been a total eclipse visible in the continental United States since 1979. The majority of the North American readership hasn’t even had the chance to see one in their lifetimes.
But of course it goes beyond the value of mere scarcity. Being able to understand, and predict an eclipse conveys a great deal about the progress of humanity. For millennia, a solar eclipse was a shocking (perhaps horrifying) experience. But through the scientific process of observation, the advances of record keeping, and the work of untold numbers of early astronomers we learned. Solar and Lunar eclipses were events that challenged thinking and became some of the earliest scientific discoveries.
This type of advancement hasn’t stopped. Even this year the application of the newest technology is present. Just one example that will turn your head is the shadow simulation that we saw in January. The moon isn’t a perfect sphere, and the combination of its landscape and that of the Earth means the outer fringes of totality will not be straight lines, but an undulating path. It’s a small detail realized in a profound way by a citizen scientist so that we may all enjoy it. Isn’t being alive now absolutely stunning?
Boil it Down for Me
So no, watching a rock cast a shadow won’t blow your mind. But understanding that the movement of this shadow isn’t random, that we didn’t always understand it, and that there are huge forces at work here will humble your modern brain and leave you awestruck. It’s a rare chance to observe with your own senses the evidence of huge masses governed by gigantic gravitational forces at incomprehensible distances through the simple act of a shadow racing across the landscape.
Be there, and make it a celebration of science, humanity, and your own life experience. Share your eclipse meetup now!
July 20th, 1969 was the day that people from Earth set foot on different soil for the first time. Here we are 48 years later, and the world’s space programs are — well — not very close to returning to the moon. If you aren’t old enough to remember, it was really amazing. The world was in a lot of turmoil in the 1960s (and still is, of course) but everyone stopped to look at the sky and listen to the sound of [Neil Armstrong] taking that first step. It was shocking in a good way and almost universally observed. Practically everyone in the world was focused on that one event. You can see some of that in the NASA video, below.
Space flight was an incredible accomplishment, but it paled in comparison with the push to actually landing a person on the moon and bringing them home safely. The effort is a credit to the ability of people to work together (on the order of thousands of minds) to overcome a difficult challenge. We can learn a lot from that alone, and it makes a compelling argument to continue taking on tough problems. Today, as we remember the Apollo landings, let’s take a moment to recognize what came of it beyond an iconic boot-print in the floury lunar soil.
The I/O capabilities built into most microcontrollers make it easy to measure the analog world. Say you want to build a data logger for temperature. All you need to do is get some kind of sensor that has a linear voltage output that represents the temperature range you need to monitor — zero to five volts representing 0° to 100°C, perhaps. Hook the sensor up to and analog input, whip up a little code, and you’re done. Easy stuff.
Now put a twist on it: you need to mount the sensor far from the microcontroller. The longer your wires, the bigger the voltage drop will be, until eventually your five-volt swing representing a 100° range is more like a one-volt swing. Plus your long sensor leads will act like a nice antenna to pick up all kinds of noise that’ll make digging a usable voltage signal off the line all the harder.
Luckily, industrial process engineers figured out how to deal with these problems a long time ago by using current loops for sensing and control. The most common standard is the 4-mA-to-20-mA current loop, and here we’ll take a look at how it came to be, how it works, and how you can leverage this basic process control technique for your microcontroller projects.
I recently had the opportunity to attend a lecture by Harvard Professor Paul Horowitz. It’s a name you likely recognize. He is best known for his iconic book the Art of Electronics which is often referred to not by its name but by the last names of the authors: “Horowitz and Hill”.
Beyond that, what do you know about Paul Horowitz? Paul is an electrical engineer and physicist and Paul has spent much of his storied career learning and practicing electronics for the purpose of finding intelligent extra terrestrial life.
We’d never seen an iconoscope before. And that’s reason enough to watch the quirky Japanese, first-person video of a retired broadcast engineer’s loving restoration. (Embedded below.)
Quick iconoscope primer. It was the first video camera tube, invented in the mid-20s, and used from the mid-30s to mid-40s. It worked by charging up a plate with an array of photo-sensitive capacitors, taking an exposure by allowing the capacitors to discharge according to the light hitting them, and then reading out the values with another electron scanning beam.
The video chronicles [Ozaki Yoshio]’s epic rebuild in what looks like the most amazingly well-equipped basement lab we’ve ever seen. As mentioned above, it’s quirky: the iconoscope tube itself is doing the narrating, and “my father” is [Ozaki-san], and “my brother” is another tube — that [Ozaki] found wrapped up in paper in a hibachi grill! But you don’t even have to speak Japanese to enjoy the frame build and calibration of what is probably the only working iconoscope camera in existence. You’re literally watching an old master at work, and it shows.
Everyone knows that writing programs that exploit the GPU (Graphics Processing Unit) in your computer’s video card requires special arcane tools, right? Well, thanks to [Matthew Saw], [Fazil Sapuan], and [Cheah Eugene], perhaps not. At a hackathon, they turned out a Javascript library that allows you to create “kernel” functions to execute on the GPU of the target system. There’s a demo available with a benchmark which on our machine sped up a 512×512 calculation by well over five times. You can download the library from the same page. There’s also a GitHub page.
The documentation is a bit sparse but readable. You simply define the function you want to execute and the dimensions of the problem. You can specify one, two, or three dimensions, as suits your problem space. When you execute the associated function it will try to run the kernels on your GPU in parallel. If it can’t, it will still get the right answer, just slowly.
