Sine Waves, Squares Waves, and the Occasional FFT

I became aware of harmonics and the sound of different shaped waveforms early in my electronics career (mid 1970’s) as I was an avid fan of [Emerson Lake and Palmer], [Pink Floyd], [Yes], and the list goes on. I knew every note of [Karn Evil 9] and could hear the sweeping filters and the fundamental wave shapes underneath it.

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I remember coming to the understanding that a square wave, which is a collection of fundamental and (odd) harmonics frequencies, could then be used to give an indication of frequency response. If the high frequencies were missing the sharp edges of the square wave would round off. The opposite was then true, if the low frequencies were missing the square wave couldn’t “hold” its value and the top plateau would start to sag.

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HOPE X: Citizens Band Microwave Spectrum And Free Internet For All

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The bulk of HOPE X was the talks, but arguably the far more interesting aspect of thousands of hackers and tinkerers under one roof is talking to everyone about what they’re doing. One guy hanging out at HOPE gave a quick lightning talk to a few people about something very interesting: something the FCC is pushing through that’s open to just about everything: it’s the FCC’s new CB radio service (you’ll want to click the presentation link at the very top of the page), giving anyone, not just people with a radio license, access to a huge swath of microwave spectrum.

The short version of the talk was the fact the FCC is extremely interested in opening up 100 to 200 MHz of spectrum at 3.5 GHz. The idea is to create something like cellular service that can either be implemented by companies, or normal, everyday people. The initial goal of this is to provide -possibly- free Internet to anyone with the right USB dongle. Since it’s just radio, and open to everyone, just about anything can be implemented.

This is something the FCC, Google, Microsoft, and a whole bunch of startups are extremely interested in, and the fact that about half of the spectrum will be open to anyone creates some interesting opportunities. A community-based freenet of wireless Internet links becomes an easy solution, and since the hardware to access 3.5 GHz is similar to other hardware that’s already available means building your own wireless ISP could be relatively easy in 12 to 18 months.

A transcript of the lightning talk is available below.

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The HellZXchreiber

HellZXschreiber

Hellschreiber – German for ‘light pen’ – was developed in the 20s as a way to transmit text in a way that was much more robust than the teletypes of the time. These devices were used to great effect by the Germans in WWII, and later became popular with wire services and was used until the 80s. The fax machine then happened, and no one really cared about Hellschreiber, save for a few plucky amateur radio enthusiasts.

In the early 90s, a few of these amateur radio enthusiasts realized they could use their personal computers to communicate with this extremely simple protocol that’s also very resilient against interference and weak radio links. [Danjovic] is following in their footsteps by decoding Hellschreiber on an old ZX Spectrum clone.

[Danjovic] tested his code with the sound sample found in the Hallschreiber wiki article and some text generated by Fldigi. Everything works beautifully, an [Dan] can even change the intensity of the text with the volume control – a very useful feature should the HellZXchreiber ever make it out into the field.

Source and image files available for all you strange Speccy fans. Everyone else can check out the videos below.

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A cold cathode audio visualizer

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Finally, cold cathode lights can be used for much more than illuminating the inside of your computer or making your whip look like it can hover. [James] discovered if he varied the voltage going into the inverter, only a certain amount of the tube would light up. Give a hacker an interesting observation and enough time, and eventually he’ll come up with something really cool. In this case, it’s a cold cathode audio visualizer, powered by fluorescent tubes doing unexpected things.

The build details are a little scant, but we were able to coax an imgur album of [James]‘ build. He’s using these 20″ CCFL lights with the stock digital inverters replaced with TDK CCFL inverters.

The digital control of this build is provided by an Arduino Mega and a custom shield. We’re guessing the graphic EQ is provided by an MSGEQ7 chip, and the inverters themselves are powered through the Mega’s PWM pins. It’s a lot like an IN-9 Nixie graphic EQ, only much, much bigger. [James] is planning a larger version of this build, dubbed the Mega speKtrum and we can’t wait to see that build along with a proper writeup.

Weightless, the hopefully-not-vaporware Internet of Things chip

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Imagine a single chip able to interface with your Ethernet, USB, and serial devices, turn those connections into wireless radio signals with miles of range, able operate off a single AA battery, and costs less than $2. That’s the promise of the Weightless special interest group that wants to put several hopefully not vaporware radio chips in the hands of everyone on the planet.

Long-range wireless networks are a tricky thing; for home networks, Bluetooth and WiFi reign supreme. Venturing into the outdoors, or really any place more than a few hundred feet from a WiFi repeater is a challenge, though. If you’re trying to send data to a fleet of automobiles, track an endangered animal, or make a smart power grid, your only real option is a cell phone tower with very high costs in hardware and battery life.

Weightless hopes to change that with a small radio chip that includes a MAC, PHY, and all the components necessary to turn just about any digital connection into a wireless link between devices. The radio will operate in the spectrum left behind by UHF TV (470 – 790MHz), and the folks working on already have some reference designs etched into silicon.Don’t expect this to replace WiFi, cellular, or Bluetooth, though: according to the getting to know Weighless book, the designers are aiming for a data rate of only a few kB/s.

Still, it’s a great use of now unused spectrum, and would fill a huge gap in what is readily possible with homebrew Internet of Things things.

Tip ‘o the hat to [Mark] for sending this one in.

Yukikaze, music visualizations

[Taichi Inoue] put together this beautiful visualization system called Yukikaze, japanese for “snow wind”. Basically a spectrum analyzer, Yukikaze is delightful to watch. We would love to see what kind of response he gets, as most of the footage shows very slowly changing smooth jazz. While we don’t think he gets crisp EQ visualizations out of this since it is a single large chamber, we still think it is amazing to watch.

[via MakeZine]

Turn your Playstation 3 into Linux-based Lab Equipment

In a two-part series called “PS3 Fab-to-lab” on IBM’s awesome developerWorks website, [Lewin] explains how to use the Cell Broadband Engine in a PS3 to create an audio-bandwidth spectrum analyzer and function generator. The set up consists of Yellow Dog Linux, an NTSC television, and an external USB sound card to provide the inputs of the spectrum analyzer and the outputs of the function generator. The sound card driver is written to simply capture or send the info in question (audio range only) and the NTSC television as the graphical interface. This hack involves a lot of coding with hardly any example code provided. The article is more of a guide than anything. If anyone gets this working, let us know!

[via Digg]

[photo: Malcom Tredinnick]