Curated

76 Articles

Hackaday’s finest original content articles curated by the Hackaday editors

I2C Bus Splitting With A More Professional Touch

August 12, 2015 by 23 Comments

Last week, I covered some of the bitter details of an interesting hack that lets us split up the I²C clock line into multiple outputs with a demultiplexer, effectively giving us “Chip Selects” for devices with the same address.

This week, I figured it’d be best to layout a slightly more practical method for solving the same problem of talking to I²C devices that each have the same address.

I actually had a great collection of comments mention the same family of chips I’m using to tackle this issue, and I’m glad that we’re jumping off the same lead as we explore the design space.

Recalling the Work of Our Predecessors

Before figuring out a clever way of hacking together our own solution, it’s best to see if someone before us has already gone through all of the trouble to solve that problem. In this case–we’re in luck–so much that the exact bus-splitting behavior we want is embedded into a discrete IC, known as the PCA9547.

chip_reverence

It’s worth remembering that our predecessors have labored tirelessly to create such a commodity piece of silicon.

The PCA9547 (PDF) is an octal, I²C bus multiplexer, and I daresay, it’s probably the most practical solution for this scenario. Not only does the chip provide 8 separate buses, up to seven more additional PCA9547s can be connected to enable communication with up to 64 identical devices! What’s more, the PCA9547 comes with the additional benefit of being compatible with both 3.3V and 5V logic-level devices on separate buses. Finally, as opposed to last week’s “hack,” each bus is bidirectional, which means the PCA9547 is fully compliant with the I²C spec.

Selecting one of the eight I²C buses is done via a transfer on the I²C bus itself. It’s worth mentioning that this method does introduce a small amount of latency compared to the previous clock-splitter solution from last week. Nevertheless, if you’re planning to read multiple devices sequentially from a single bus anyway, then getting as close-as-possible to a simultaneous read/write from each device isn’t likely a constraint on your system.

 

With a breakout board to expose the pads, I mocked up a quick-n-dirty Arduino Library to get the conversation started and duplicated last week’s demo.

Happily enough, with a single function to change the bus address, the PCA9547 is pretty much a drop-in solution that “just works.” It’s definitely reassuring that we can stand on the shoulders of our chip designers to get the job done quickly. (They’ve also likely done quite a bit more testing to ensure their device performs as promised.) Just like last week, feel free to check out the demo source code up on Github.

Until next time–cheers!

Getting Started With ARM Using Mbed

August 11, 2015 by 80 Comments

Even though the Arduino was hardly the first 8 bit microcontroller board to support a bootloader and the C/C++ language, it quickly became the de facto standard for hobby-level microcontrollers as well as a common choice for one-off or prototype projects. I’m sure there are a lot of reasons why this occurred, but in my mind there were three major reasons: price, availability of lots of library and sample code, and the existence of a simplified GUI IDE that you could install in a few minutes. The build process is simple, too, even though if you ever have to actually figure it out, it is quite ugly. For most people, it works, and that makes it not ugly.

I like the ATMega chips. In fact, I had boards based around the ATMega8 and a bootloader way before there was an Arduino. However, they are fairly small parts. It is true that the Arduino infrastructure has grown to support more ATMega chips, many with more memory and I/O and clock speeds. However, 32-bit processors are getting inexpensive enough that for all but the simplest or highest volume projects, you should be thinking about using 32-bit.

If you’ve tried to go that route before, you’ve probably been daunted by the price, especially the price of development tools. Your alternative is to roll your own tool chain which is very doable (and there are some nice scripts out there that will help you). You also need to worry about libraries and how to integrate them. Not to mention, many of the advanced processors require a lot of setup to get, say, an A/D converter turned on. Most processors keep things they aren’t using turned off, and each pin requires setup to select the 4 or 5 things shared on that pin.

All of this has been a barrier to entry. The vendors have all figured this out, though, and many have tried to build tools aimed at breaking up the Arduino market ranging from inexpensive development boards to code-generating wizards, to full blown IDEs. I want to tell you (and show you, in the video below) how you can make the jump from 8-bit to 32-bit much easier than you might think.

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DEF CON Vs IoT: On Hackability And Security

August 10, 2015 by 16 Comments

Ahh DEF CON! One group of hackers shows off how they’ve broken into all sorts of cool devices and other hackers (ahem… “security professionals”) lament the fact that the first group were able to do so. For every joyous “we rooted the Nest thermostat, now we can have fun” there’s a doom-mongering “the security of network-connected IoT devices is totally broken!”.

And like Dr. Jekyll and Mr. Hyde, these two sides of the hacker persona can coexist within the same individual. At Hackaday, we’re totally paranoid security conscious, but we also like to tinker with stuff. We believe that openness and security are best friends forever. If you can open it, you can see if it’s well-made inside, at least in principle. How do we reconcile this with the security professional’s demand for devices that only accept signed binary firmware updates so that they can’t be tampered with?

We’ve got no answers, but we’ve got plenty of questions. Read on, and let us know what you think.

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Logic Noise: 4046 Voltage-Controlled Oscillator, Part One

August 7, 2015 by 23 Comments

In this session of Logic Noise, we’ll be playing around with the voltage-controlled oscillator from a 4046 phase-locked loop chip, and using it to make “musical” pitches. It’s a lot of bang for the buck, and sets us on the path toward much more interesting circuits in the future. So watch the intro video right after the break, and we’ll dig straight in.

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Hacking A Universal Assembler

August 6, 2015 by 30 Comments

I have always laughed at people who keep multitools–those modern Swiss army knives–in their toolbox. To me, the whole premise of a multitool is that they keep me from going to the toolbox. If I’ve got time to go to the garage, I’m going to get the right tool for the job.

Not that I don’t like a good multitool. They are expedient and great to get a job done. That’s kind of the way I feel about axasm — a universal assembler I’ve been hacking together. To call it a cross assembler hack doesn’t do it justice. It is a huge and ugly hack, but it does get the job done. If I needed something serious, I’d go to the tool box and get a real assembler, but sometimes you just want to use what’s in your pocket.

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Quantum Mechanics In Your Processor: Quantum Computing

August 6, 2015 by 54 Comments

Not long after [Hitler] took control of Germany, his party passed laws forbidding any persons of Jewish descent from holding academic positions in German Universities. This had the effect of running many of the world’s smartest people out of the country, including [Albert Einstein]. Einstein settled into his new home in Princeton, and began to seek out bright young mathematicians to work with, for he still had a bone to pick with [Niels Bohr] and his quantum theory. It wasn’t long until he ran into an American, [Nathan Rosen] and a Russian, [Boris Podolsky]. The trio would soon lay before the world a direct challenge that would strike at the very core of quantum theory’s definition of reality. And unlike the previous challenges, this one would not be so easily dismissed by [Bohr].

Need a bit of catching up? You can check out Complimentarity as well as Tunneling and Transistors but  that is just some optional background for wrapping your head around Quantum Computing.

The EPR Argument

On May 4th, 1935, the New York Times published an article entitled “Einstein Attacks Quantum Theory”, which gave a non technical summary of the [Einstein-Podolsky-Rosen] paper. We shall do something similar.

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Embed With Elliot: The Static Keyword You Don’t Fully Understand

August 4, 2015 by 70 Comments

One of our favorite nuances of the C programming language (and its descendants) is the static keyword. It’s a little bit tricky to get your head around at first, because it can have two (or three) subtly different applications in different situations, but it’s so useful that it’s worth taking the time to get to know.

And before you Arduino users out there click away, static variables solve a couple of common problems that occur in Arduino programming. Take this test to see if it matters to you: will the following Arduino snippet ever print out “Hello World”?

void loop()
{
	int count=0;
	count = count + 1;
	if (count > 10) {
		Serial.println("Hello World");
	}
}

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