An acousto-optic tunable filter and laser

Acousto-Optic Filter Uses Sound To Bend Light

We all know that light and sound are wave phenomena, but of very different kinds. Light is electromechanical in nature, while sound is mechanical. Light can travel through a vacuum, while sound needs some sort of medium to transmit it. So it would seem that it might be difficult to use sound to modify light, but with the right equipment, it’s actually pretty easy.

Easy, perhaps, if you’re used to slinging lasers around and terms like “acousto-optic tunable filter” fall trippingly from your tongue, as is the case for [Les Wright]. An AOTF is a device that takes a radio frequency input and applies it to a piezoelectric transducer that’s bonded to a crystal of tellurium oxide. The RF signal excites the transducer, which vibrates the TeO2 crystal and sets up a standing wave within it. The alternating bands of compressed and expanded material within the crystal act like a diffraction grating. Change the excitation frequency, and the filter’s frequency changes too.

To explore the way sound can bend light, [Les] picked up a commercial AOTF from the surplus market. Sadly, it didn’t come with the RF driver, but no matter — a few quick eBay purchases put the needed RF generator and power amplifier on his bench. The modules went into an enclosure to make the driver more of an instrument and less of a one-off, with a nice multi-turn pot and vernier knob for precise filter adjustment. It’s really kind of cool to watch the output beam change colors at the twist of a knob, and cooler still to realize how it all works.

We’ve been seeing a lot of [Les]’ optics projects lately, from homemade TEA lasers to blasting the Bayer filter off a digital camera, each as impressive as the last! Continue reading “Acousto-Optic Filter Uses Sound To Bend Light”

Piezo Pickup Makes Wax Records Easy To Digitize

Sound recording and playback have come a long way in the last century or so, but it’s fair to say there’s still a lot of interesting stuff locked away on old recordings. Not having a way to play it back is partly to blame; finding an antique phonograph that plays old-timey cylinder recordings is pretty hard. But even then, how do you digitize the output of these fragile, scratchy old recordings?

As it happens, [Jan Derogee] is in a position to answer these questions, with an antique phonograph and a bunch of Edison-style wax cylinders with voices and music from a bygone era locked away on them. It would be easy enough to just use the “reproducer” he previously built and set up a microphone to record the sound directly from the phonograph’s trumpet, but [Jan] decided to engineer a better solution. By adding the piezo element from an electronic greeting card to his reproducer, potted with liberal quantities of epoxy and padded with cotton, the piezo pickup was attached to the phonograph arm in place of the original stylus and trumpet. The signal from the piezo element was strong enough to require a shunt resistor, allowing it to be plugged directly into the audio input jack on a computer. From there it’s just an Audacity exercise, plus dealing with the occasional skipped groove.

We appreciate [Jan]’s effort to preserve these recordings, as well as the chance to hear some voices from the past. We’re actually surprised the recording sound as good as they do after all this time — they must have been well cared for.

Continue reading “Piezo Pickup Makes Wax Records Easy To Digitize”

A Scientist Made An Artificial Black Hole In The Lab, And You Won’t Believe What Happened Next

OK, that was a little click-baity, but then again, so was the announcement this week that a scientist had confirmed Hawking radiation with a lab-grown black hole. It sure got our attention, at least.

As it turns out, the truth is both less and more than meets the eye. The article above was eventually edited to better reflect the truth that, alas, we have not yet found a way to create objects so massive that even light cannot escape them. Instead, physicist [Jeff Steinhauer] and colleagues at the Technion-Israel Institute of Technology have developed an acoustic model of black holes, which is what was used to observe the equivalent of Hawking radiation for the first time. Hawking radiation is the theoretical exception to the rule that nothing makes it out of a black hole and would imply that black holes evaporate over time. The predicted radiation would be orders of magnitude weaker than the background radiation, though, making it all but impossible to detect.

That’s where [Steinhauer]’s sonic black holes come in. In these experiments, phonons, packets of mechanical vibrations that stand in for photons, are trapped in a fast-moving stream of fluid. The point in the stream where its speed straddles the local speed of sound is the equivalent to a real black hole’s event horizon; phonons inside that boundary can never escape. Except, of course, for the sonic equivalent of Hawking radiation, which the researchers found after 97,000 attempts.

When we first stumbled upon this story, we assumed a lab-grown black hole, even an acoustic analog, would take a CERN’s-worth of equipment to create. It turns out to be far simpler than that; [Steinhauer], in fact, built his black hole machine singlehandedly from relatively simple equipment. The experiments do require temperatures near absolute zero and a couple of powerful lasers, so it’s not exactly easy stuff; still, we can’t help but wonder if sonic black holes are within the reach of the DIY community. Paging [Ben Krasnow] and [Sam Zeloof], among others.

[Featured image credit: Nitzan Zohar, Office of the Spokesperson, Technion]

Raspberry Pi Crazy Guitar Rig Turns You Into A Hard ‘N Heavy One-Man Band

It’s a common problem: you’re at a party, there’s a guitar, and your plan to impress everyone with your Wonderwall playing skills is thwarted by the way too loud overall noise level. Well, [Muiota betarho] won’t have that issue ever again, and is going to steal the show anywhere he goes from now on with his Crazy Guitar Rig 2.0, an acoustic guitar turned electric — and so much more — that he shows off in three-part video series on his YouTube channel. For the impatient, here’s video 1, video 2, and video 3, but you’ll also find them embedded after the break.

To start off the series, [Muiota betarho] adds an electric guitar pickup, a set of speakers, and an amplifier board along with a battery pack into the body of a cheap acoustic guitar. He then dismantles a Zoom MS-50G multi-effect pedal and re-assembles it back into the guitar itself with a 3D-printed cover. Combining a guitar, effect pedal, amp and speaker into one standalone instrument would make this already an awesome project as it is, but this is only the beginning.

Touch screen and controls closeup
RPi touch screen running SunVox, plenty of buttons, and integrated multi-effect pedal on the left

So, time to add a Raspberry Pi running SunVox next, and throw in a touch screen to control it on the fly. SunVox itself is a free, but unfortunately not open source, cross-platform synthesizer and tracker that [Muiota betarho] uses to add drum tracks and some extra instruments and effects. He takes it even further in the final part when he hooks SunVox up to the Raspberry Pi’s GPIO pins. This allows him to automate things like switching effects on the Zoom pedal, but also provides I/O connection for external devices like a foot switch, or an entire light show to accompany his playing.

Of course, adding a magnetic pickup to an acoustic guitar, or generally electrifying acoustic instruments like a drum kit for example, isn’t new. Neither is using a single-board computer as effect pedal or as an amp in your pocket. Having it all integrated into one single device on the other hand rightfully earns this guitar its Crazy Guitar Rig name.

(Thanks for the tip, [alex]!)

Continue reading “Raspberry Pi Crazy Guitar Rig Turns You Into A Hard ‘N Heavy One-Man Band”

Your Own Electronic Drum Kit

[Jake_Of_All_Trades] wanted to take up a new drumming hobby, but he didn’t want to punish his neighbors in the process. He started considering an electric drum kit which would allow him to practice silently but still get some semblance of the real drumming experience.

Unfortunately, electric drum kits are pretty expensive compared to their acoustic counterparts, so buying an electric kit was a bit out of the question. So, like any good hacker, he decided to make his own.

He found a pretty cheap acoustic drum kit on Craigslist and decided to convert it to electric. He thought this would be a perfect opportunity to learn more about electric drum kits in general and would allow him to do as much tweaking as he wanted to in order to personalize his experience. He also figured this would be a great way to get the best of both worlds. He could get an electric kit to practice whenever he wanted without disturbing neighbors and he could easily convert back to acoustic when needed.

First, he had to do a bit of restorative work with the cheap acoustic kit he found on eBay since it was pretty worn. Then, he decided to convert the drum heads to electric using two-ply mesh drum heads made from heavy-duty fiberglass screen mesh. The fiberglass screen mesh was cheap and easy to replace in the event he needed to make repairs. He added drum and cymbal triggers with his own DIY mechanism using a piezoelectric element, similar to another hack we’ve seen. These little sensors are great for converting mechanical to electrical energy and can feed directly into a GPIO to detect when the drum or cymbal was struck. The electrical signal is then interpreted by an on-board signal processing module.

All he needed were some headphones or a small amplifier and he was good to go! Cool hack [Jake_Of_All_Trades]!

While you’re here, check out some of our best DIY musical projects over the years.

Behold A 3D Display, Thanks To A Speeding Foam Ball

We’ve seen 3D image projection tried in a variety of different ways, but this is a new one to us. This volumetric display by Interact Lab of the University of Sussex creates a 3D image by projecting light onto a tiny foam ball, which zips around in the air fast enough to create a persistence of vision effect. (Video, embedded below.) How is this achieved? With a large array of ultrasonic transducers, performing what researchers call ‘acoustic trapping’.

This is the same principle behind acoustic levitation devices which demonstrate how lightweight objects (like tiny polystyrene foam balls) can be made to defy gravity. But this 3D display is capable of not only moving the object in 3D space, but doing so at a high enough speed and with enough control to produce a persistence of vision effect. The abstract for their (as yet unreleased) paper claims the trapped ball can be moved at speeds of up to several meters per second.

It has a few other tricks up its sleeve, too. The array is capable of simultaneously creating sounds as well as providing a limited form of tactile feedback by letting a user touch areas of high and low air pressure created by the transducers. These areas can’t be the same ones being occupied by the speeding ball, of course, but it’s a neat trick. Check out the video below for a demonstration.
Continue reading “Behold A 3D Display, Thanks To A Speeding Foam Ball”

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Hackaday Links: November 10, 2019

In the leafy suburbs of northern Virginia, a place ruled by homeowner’s associations with tremendous power to dictate everything from the color of one’s front door to the length of grass in the lawn, something as heinous as garage doors suddenly failing to open on command is sure to cause a kerfuffle. We’ve seen this sort of thing before, where errant RF emissions cause unintentional interference, and such stories aren’t terribly interesting because the FCC usually steps in and clears things up. But this story is a little spicier given the source of the interference: Warrenton Training Center, a classified US government communications station located adjacent to the afflicted neighborhood. WTC is known to be a CIA signals intelligence station, home to spooks doing spooky stuff, including running high-power numbers stations. The interference isn’t caused by anything as cloak-and-dagger as that, though; rather, it comes from new land-mobile radios that the Department of Defense is deploying. The new radios use the 380-400 MHz band, which is allocated to the Federal Government and unlicensed Part 15 devices, like garage door remotes. But Part 15 rules, which are clearly printed on every device covered by them, state that the devices have to accept unwanted interference, even when it causes a malfunction. So the HOA members who are up in arms and demanding that the government buy them new garage door openers are likely to be disappointed.

Speaking of spooks, if you’re tired of the prying electronic eyes of facial recognition cameras spoiling your illusion of anonymity, have we got a solution for you. The Opt-Out Cap is the low-tech way to instantly change your face for a better one, or at least one that’s tied to someone else. In a move which is sure not to arouse suspicion in public, doffing the baseball cap deploys a three-piece curtain of semi-opaque fabric, upon which is printed the visage of someone who totally doesn’t look creepy or sketchy in any way. Complete instructions are provided if you want to make one before your next trip to the ATM.

It’s always a great day when a new Ken Shirriff post pops up in our feed, and his latest post is no exception. In it, Ken goes into great detail about the history of the 80×24 (or 25) line standard for displays. While that may sound a bit dry, it’s anything but. After dispelling some of the myths and questionable theories of the format’s origin – sorry, it’s not just because punch cards had 80 columns – he discusses the transition from teletypes to CRTs, focusing on the very cool IBM 2260 Display Station. This interesting beast used an acoustic delay line made of 50′ (15 m) of nickel wire. It stored data as a train of sound pulses traveling down the wire, which worked well and was far cheaper than core memory, even if it was susceptible to vibrations from people walking by it and needed a two-hour warm-up period before use. It’s a fascinating bit of retrocomputing history.

A quick mention of a contest we just heard about that might be right up your alley: the Tech To Protect coding challenge is going on now. Focused on applications for public safety and first responders, the online coding challenge addresses ten different areas, such as mapping LTE network coverage to aid first responders or using augmented reality while extricating car crash victims. It’s interesting stuff, but if you’re interested you’ll have to hurry – the deadline is November 15.

And finally, Supercon starts this week! It’s going to be a blast, and the excitement to hack all the badges and see all the talks is building rapidly. We know not everyone can go, and if you’re going to miss it, we feel for you. Don’t forget that you can still participate vicariously through our livestream. We’ll also be tweet-storming and running a continuous chat on to keep everyone looped in.