Passive WiFi On Microwatts

February 26, 2016 by Elliot Williams 30 Comments

A lot of you use WiFi for your Internet of Things devices, but that pretty much rules out a battery-powered deployment because WiFi devices use a lot of juice. Until now. Researchers at the University of Washington have developed a passive WiFi implementation that uses only microwatts per device.

Working essentially like backscatter RFID tags do, each node has a WiFi antenna that can be switched to either reflect or absorb 2.4 GHz radiation. Your cell phone, or any other WiFi device, responds to this backscattered signal. All that’s missing is a nice steady signal to reflect.

A single, plugged-in unit provides this carrier wave for multiple WiFi sensor nodes. And here’s the very clever part of the research: to keep the carrier from overwhelming the tiny modulated signal that’s coming from the devices, the plugged-in unit transmits off the desired frequency and the battery-powered units modulate that at just the right difference frequency so that the resulting (mixed) frequency is in the desired WiFi band.

If you’re a radio freak, you’ll recognize the WiFi node’s action being just like a frequency mixer. That’s what the researchers (slightly mysteriously) refer to as the splitting of the analog transmission stage from the digital. The plugged-in unit transmits the carrier, and the low-power nodes do the mixing. It’s like a traditional radio transmitter, but distributed. Very cool.

There’s a bunch more details to making this system work with consumer WiFi, as you’d imagine. The powered stations are responsible for insuring that there’s no collision, for instance. All of these details are very nicely explained in this paper (PDF). If you’re interested in doing something similar, you absolutely need to give it a read. This idea will surely work at lower frequencies, and we’re trying to think of a reason to use this distributed transmitter idea for our own purposes.

And in case you think that all of this RFID stuff is “not a hack”, we’ll remind you that (near-field) RFID tags have been made with just an ATtiny or with discrete logic chips. The remotely-powered backscatter idea expands the universe of applications.

Thanks [Ivan] for the tip!

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Frackers: Inside The Mind Of The Junk Hacker

February 25, 2016 by Elliot Williams 116 Comments

Hackers can be a diverse bunch. My old hackerspace had folks ranging from NSA employees (ahem, independent security contractors) to space-probe pilots to anarchist vegan punks. And we all got along because we shared a common love for what we’re doing. One summer night we were out late in Adams Morgan and my vegan-punk friend reaches into the trash can and pulls out a discarded pepperoni Jumbo Slice.

“Wait a minute! Vegans don’t eat pepperoni pizza with cheese.” But my friend was a “freegan” — a vegan who, for ethical reasons, won’t buy meat or milk but who also won’t turn it down if it’s visibly going to waste. It’s actually quite a practical and principled moral proposal if you think about it: he’s not contributing to the use of animals that he opposes, but he gets to have a slice of pizza just the same. And fishing a slice of pizza, in a cardboard container, off the top of the trashcan isn’t as gross as you’d imagine, although it pays to be picky.

A Fracker is Born

That was the night that we realized we all had something deeper in common: we were all “frackers”. If you’ve been around hackers long enough, you’ll have noticed this tendency, but maybe you’ve never put a name to it. Tearing something apart, even if you might break it in the process, isn’t a problem if you fished it out of the e-waste stream to begin with. If you’re able to turn it into something, so much the better. It’s all upside. Need practice de-soldering tricky ICs? Looking for a cheap target to learn reverse engineering on? Off to the trashcan! No hack is too dirty, no method too barbaric. It’s already junk, and you’re a fracker.

Do you have a junk shelf where you keep old heatsinks in case you need to cut some up and use it? Have you used a heat gun more frequently for harvesting parts than for stripping paint? Do you know that certain satisfaction that you get from pulling some old tech out of the junk pile and either fixing it up again or, better yet, making it do something else? You might just be a fracker too.

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NES Light Gun Turned (Video) Synthesizer

February 25, 2016 by Elliot Williams 7 Comments

[Russell Kramer] made our day today. We’re tremendous fans of minimalism in electronics design, dirty noise hacks, and that old NES light gun. He’s posted up a project that combines all three to make a light-gun controlled, VGA video display that makes bleepy-bloopy noises to boot. Check out the video below!

To appreciate this hack, you really need to read through the project logs in detail. Start with the VGA signal creation, for instance. The easiest way to go these days is to throw a microcontroller at the problem. But because he’s done that to death, [Russell] takes a step back thirty years and generates the sync pulses periodically with a relaxation oscillator and a binary counter IC. The rest of the build follows this aesthetic choice: everything is op amps and CMOS logic. The rainbow effect, for instance, is created from the audio signal through a three-stage, 120-degree phase-shift oscillator sent to the R, G, and B channels. Kudos!

The high-level overview is that the light intensity and position hitting the gun’s sensor is converted into a voltage that drives an audio-frequency oscillator. This audio output is then piped back into the video generator. Watching the video, it’s obvious that pointing the gun at different parts of the screen changes the pitch, but playing a given pitch is nearly impossible on this thing with all the feedback going on. [Russell] added a bit of more control into the system — when the gun’s trigger is pulled, it registers full-brightness regardless of the video input — but even so, we’d be hard-pressed to play “Mary Had a Little Lamb”.

But that’s not the point. The point is awesome, light-gun-waving noisy madness set to a responsive colorful video background. And that’s been achieved in spades!

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Quickie WiFi Scanner

February 24, 2016 by Elliot Williams 4 Comments

File this project under “Getting Stuff Done” rather than “Shiniest Things”. [filid] works with a local free-WiFi access group, and wanted to map out the signal strength (RSSI) and coverage of their installations. This is a trivial task for an ESP8266, and it was even easier for [filid] because he had already written some WiFi scanner code for the same hardware.

Basically, the device is a Neopixel ring connected to an ESP8266. If it detects a router that’s part of the Freifunk München network, it displays the RSSI on the ring in an attractive circular “bargraph”. When it doesn’t detect a Freifunk node, it displays the number of WiFi routers that it finds. It dumps a lot more detail over the serial port.

The code is short and sweet. Take a look if you’re just getting started with networking using the Arduino firmware on an ESP. Even if you don’t live in Munich, you’ll be able to tweak it to your own situation in a few seconds.

We want to see a GPS and an SD card added to this one, for a standalone wardriving-with-purpose setup. And while we admit that the small form-factor is probably appropriate for this project, how much cooler would it be if it glowed blue like Bilbo’s “Sting”?

When Are 8 Bits More Than 32?

February 24, 2016 by Elliot Williams 152 Comments

Whenever we write up a feature on a microcontroller or microcontroller project here on Hackaday, we inevitably get two diametrically opposed opinions in the comments. If the article featured an 8-bit microcontroller, an army of ARMies post that they would do it better, faster, stronger, and using less power on a 32-bit platform. They’re usually right. On the other hand, if the article involved a 32-bit processor or a single-board computer, the 8-bitters come out of the woodwork telling you that they could get the job done with an overclocked ATtiny85 running cycle-counted assembly. And some of you probably can. (We love you all!)

When beginners walk into this briar-patch by asking where to get started, it can be a little bewildering. The Arduino recommendation is pretty easy to make, because there’s a tremendous amount of newbie-friendly material available. And Arduino doesn’t necessarily mean AVR, but when it does, that’s not a bad choice due to the relatively flexible current sourcing and sinking of the part. You’re not going to lose your job by recommending Arduino, and it’s pretty hard to get the smoke out of one.

But these days when someone new to microcontrollers asks what path they should take, I’ve started to answer back with a question: how interested are you in learning about microcontrollers themselves versus learning about making projects that happen to use them? It’s like “blue pill or red pill”: the answer to this question sets a path, and I wouldn’t recommend the same thing to people who answered differently.

For people who just want to get stuff done, a library of easy-to-use firmware and a bunch of examples to ~~crib~~ learn from are paramount. My guess is that people who answer “get stuff done” are the 90%. And for these folks, I wouldn’t hesitate at all to recommend an Arduino variant — because the community support is excellent, and someone has written an add-on library for nearly every gizmo you’d want to attach. This is well-trodden ground, and it’s very often plug-and-play.

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A Slew Of Open-Source Synthesizers

February 23, 2016 by Elliot Williams 55 Comments

Hackaday reader [Jan Ostman] has been making microcontroller-based DIY synthesizers for quite a while now. Recently, he’s opened up the source for a lot of them so that you can play along at home. All of these virtual-analog synths and soundmakers can be realized on an Arduino or AVR ATmega328 if you happen to have one lying around.

Extra parts like a keyboard, some pushbuttons, or some potentiometer knobs to twiddle won’t hurt if you’d like to make something more permanent or more obviously playable, like [Jan] does. On the other hand, if you’d just like to get your feet wet, I’ve tweaked his code to be more immediately plug-and-play. The code is straightforward enough that it’s a good learning platform. So let’s take a quick tour through three drum machines and a string synth, each of which you can build on a breadboard in just a few minutes.

To install on an Arduino UNO, fetch the zip file from this GitHub repository, and move each subfolder to your Arduino sketch directory. You’re ready to play along.

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Shoot Darts At The Shins Of Total Strangers

February 22, 2016 by Elliot Williams 15 Comments

[Michael Brumlow] found us and sent us a link. Within a few seconds, we were driving a webcam-enabled Nerf dart tank through his office and trying not to hit walls or get stepped on by his co-workers. Unfortunately, it was out of darts at the time, but you can find them all over the floor if you scout around.

All of the code details, including the link where you can test drive it yourself, are up on [Michael]’s GitHub. The brains are an Intel Edison board, and the brawns are supplied by an Arduino motor controller shield and (for the latest version) a chassis bought from China.

It runs fairly smoothly, considering the long round trip from [Michael]’s office in Texas, through wherever Amazon keeps their Web Services, over to us in Germany and back. Once we got used to the slight lag, and started using the keyboard’s arrow keys for control, we were driving around like a pro.

It’s got a few glitches still, like the camera periodically overheating and running out of WiFi distance. [Michael] said he’d try to keep it charged up and running while you give it a shot. The controls are multiplexed in the cloud, so your chance of steering it is as good as anyone else’s. It’ll be interesting to see what happens when thousands of Hackaday readers try to control it at once!

It takes a certain kind of bravery to put your telepresence robot up on the open Internets. So kudos to you, [Michael], and we hope that you manage to get some work done this week, even though you will have all of Hackaday driving into your cubicle walls.