Retrotechtacular: First laser transmitter built 50 years ago

helium-neon-laser-transmitter

Most of the time we feature hokey film footage in our Retrotechtacular series, but we think this hack is as cool today as it was fifty years ago. [Clint] wrote in to tell us about Operation Red Line. It was an experiment performed May 3rd and 4th, 1963, which means the 50th anniversary just passed a few weeks ago. The hack involved sending data (audio in this case) over long distances using a laser. But back then you couldn’t just jump on eBay and order up the parts. The team had to hack together everything for themselves.

They built their own helium-neon laser tube, which is shown on the right. The gentlemen involved were engineers at a company called Electro-Optical System (EOS) by day, and Ham radio enthusiasts by night. With the blessing of their employer they were able to ply their hobby skills using the glass blowing and optical resources from their work to get the laser up and running. With that side of things taken care of they turned to the receiving end. Using a telescope and a photomultipler they were able to pick up the beam of light at a distance of about 119 miles. The pinnacle of their achievement was modulating audio on the transmitter, and demodulating it with the receiver.

[Clint] knows the guys who did this and wrote up a look back at the project on his own blog.

Modulator box connects iPod to Tesla coil

tesla-coil-modulator

This pass through audio modulator lets you playback stereo audio on two Tesla coils. But don’t fret, you can just use mono files if you only have one coil on hand. On one side there are inputs that connect to the audio source. The other side drives the Tesla coil, switching it on and off based on the relationship between a reference voltage and the audio signal. As you can hear in the video after the break this sounds great as long as you have the right kind of source audio.

The song played in that clip is the Duke Nukem 3D theme. [Daniel] started with a MIDI file and removed the chimes and drums to make the playback a little cleaner. The demo uses just one coil because the other was destroyed during testing when feedback between the two became a problem.

For some reason this reminds us of that singing Tesla coil hat. If you’re already on our mailing list (sign up in the sidebar) you know we’re getting pretty close to unveiling our own awesome Tesla coil project. It doesn’t sing… yet.

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Script defeats minteye CAPTCHA

minteye-captcha-defeated

We hadn’t heard of minteye CAPTCHA before, but we’ve seen evidence of a script that can break the system. Minteye combines two things which you probably don’t love about the Internet: advertisements and CAPTCHA. The system uses a slider to distort an advertiser’s image. Once the slider is in just the right spot the image becomes clear and you can click on submit to see if you passed the challenge.

Challenges like this are impossible for the visually impaired, so there is usually an audio option as well. In this case the audio button will instruct you to move the slider to the right, left, or that it’s already in the correct place. [Samuirai] used the text2speech API available in Google Chrome to parse these commands. As you can see above, “movies later” is a misinterpretation of “move the slider”, but he was still able to get enough accuracy to solve the challenge. See the script in action in the video after the break.

Audio challenges have been exploited like this in the past. Check out this talk about beating reCAPTCHA through the audio option.

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Building an inexpensive Squeezebox client replacement

squeezebox-replacement-built-on-the-cheap

[Andrew] is a fan of the audio quality provided by the Squeezebox hardware. Like many he was unhappy to hear that the devices were being discontinued, but he figured out a way to build a Squeezebox client clone for less than he could have bought an original.

He set several goals for the build. Most notably he wanted the system to be low-power, noiseless, and to support audio quality of at least 96 kHz at 24 bits. What he came up with is the Pogoplug seen in between the two speakers above. It can be acquired for under $20 and it runs embedded Linux. Another member of the Squeezebox community had been working on a custom distro called SqueezePlug to turn these types of devices into Squeezebox clients. After flashing the distro and tweaking the settings [Andrew] has accomplished his goals. The one caveat is the lack of an audio out port. Above he’s using some cheap USB speakers, but higher-fidelity is possible by choosing a more expensive external USB device.

This will work nicely with that Squeezebox server you built from a Raspberry Pi.

Recording audio with Chrome using HTML5

recording-audio-with-chrome

The Dubjoy project was stopped dead in its tracks when the newest version of the Google Chrome browser stopped using Adobe’s flash plugin and transitioned to their own called Pepper Flash. The aim of development was to produce a browser-based editor for translating the audio track of a video clip. After a bit of head scratching and a lot of research they decided to try ditching the use of Flash and implemented a way to record audio using HTML5.

There were quite a few issues along the way. The initial recording technique generated raw audio files, which are not playable by Chrome’s HTML5 audio player. This can be worked around by buffering the raw audio, then converting it to a different format once the recording is finished. The user also needs to monkey with the Chromes flags to enable HTML5 audio. So they did get it working, but it’s not yet a smooth process.

We love seeing the neat stuff you can do with HTML5. One of our favorites is the use of a tablet’s accelerometer as a browser game controller.

[via Reddit]

Wireless speaker made using Arduinos and 2.4 GHz tranceivers

[Texane] picked up a 2.4 GHz transmitter/receiver pair for transmitting sensor data wirelessly. After using them in a project he wanted to try pushing them a bit to see what the limits are when it comes to higher bandwidths. He ended up building a wireless speaker that transmits audio at about 90 KB/s. That link leads to a subfolder of his git repository. The code for this project is in the RX and TX folders, with images and video in the DOC folder.

The radio hardware that he’s using is a Nordic nRF24L01P chip which is available on a breakout board from Sparkfun. [Texane] mentioned to us that the chip includes error checking, packet ACK, and automatic retransmission. But these add overhead that can slow things down. The chip does offer the option to disable these features to get lower level access to the hardware. That’s exactly what he did and he mentions that the example code he wrote for the transmitter and receiver make every cycle count. This makes us wonder if it’s the speed of the ATmega328 chip that is the bottleneck, or the transceivers themselves?

Hacking an old radar gun to interface with a laptop

[Gregory Charvat] decided to see what he could do with this old Police radar gun. It is an X-band device that broadcasts continuous waves and measures the Doppler shift as they echo back. He cracked it open to see if he could interface the output with a computer.

After a little poking around he’s able to get it connected to a 12V feed from his bench supply, and to monitor the output with an oscilloscope. He established that it draws about 0.5A in current he built a companion board which uses AA batteries for power, and provides an audio output which can be plugged into his laptop’s audio-in jack. This technique makes reading the device as easy as recording some audio. From there a bit of simple signal processing lets him graph the incoming measurement.

In the video after the break you’ll see his inspection of the hardware. After making his alterations he takes it into the field, measuring several cars, a few birds, and himself jogging.

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