You Are Your Own Tactile Feedback

[Maurin Donneaud] has clearly put a lot of work into making a large flexible touch sensitive cloth, providing a clean and intuitive interface, and putting it out there for anyone to integrate into their own project.. This pressure sensing fabric is touted as an electronic musical interface, but if you only think about controlling music, you are limiting yourself. You could teach AI to land a ‘copter more evenly, detect sparring/larping strikes in armor, protect athletes by integrating it into padding, or measure tension points in your golf swing, just to name a few in sixty seconds’ writers brainstorming. This homemade e-textile measures three dimensions, and you can build it yourself with conductive thread, conductive fabric, and piezoresistive fabric. If you were intimidated by the idea before, there is no longer a reason to hold back.

The idea is not new and we have seen some neat iterations but this one conjures ideas a mile (kilometer) a minute. Watching the wireframe interface reminds us of black-hole simulations in space-time, but these ones are much more terrestrial and responding in real-time. Most importantly they show consistent results when stacks of coins are placed across the surface. Like most others out there, this is a sandwich where the slices of bread are ordinary fabric and piezoresistive material and the cold cuts are conductive strips arranged in a grid. [Maurin] designed a custom PCB which makes a handy adapter between a Teensy and houses a resistor network to know which grid line is getting pressed.

If you don’t need flexible touch surfaces, we can help you there too.

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Creating Coherent Sound Beams, Easily

Lasers work by emitting light that is “coherent” in that it doesn’t spread out in a disorganized way like light from most sources does. This makes extremely focused beams possible that can do things like measure the distance from the Earth to the Moon. This behavior isn’t just limited to electromagnetic waves, though. [Gigs] via [CodeParade] was able to build a device that produces a tightly focused sound wave, essentially building an audio laser.

Curiously enough, the device does not emit sound in the frequency range of human hearing. It uses a set of ultrasound speakers which emit a “carrier wave” in the ultrasound frequency. However, with a relatively simple circuit a second signal in the audible frequency range is modulated on top of it, much the same way that an AM radio broadcast has a carrier wave with an amplitude modulated signal on top of it. With this device, though, the air itself acts in a nonlinear way and demodulates the signal, producing the modulated signal as audible sounds.

There are some interesting effects of using this device. First, it is extremely directional, so in order to hear sound from the device you would need to be standing directly in front of it. However, once the ultrasound beam hits a solid object, the wave is instantly demodulated and reflected from the object, making it sound like that object is making the sounds and not the device. It’s obvious that this effect is hard to experience via video, but it’s interesting enough that we’d like to have one of our own to try out. It’s not the only time that sound waves and electromagnetic waves have paired up in interesting ways, either.

Thanks to [Setvir] for the tip! Continue reading “Creating Coherent Sound Beams, Easily”

Tiny Amplifier With ATtiny

Small microcontrollers can pack quite a punch. With the right code optimizations and proper use of the available limited memory, even small microcontrollers can do things they were never intended to. Even within the realm of intended use, however, there are still lots of impressive uses for these tiny cheap processors like [Lukasz]’s audio amplifier which uses one of the smallest ATtiny packages around┬áin the video embedded below.

Since the ATtiny is small, the amplifier is only capable of 8-bit resolution but thanks to internal clock settings and the fast PWM mode he can get a sampling rate of 37.5 kHz. Most commercial amplifiers shoot for 42 kHz or higher, so this is actually quite close for the limited hardware. The fact that it is a class D amplifier also helps, since it relies on switching and filtering to achieve amplification. This allows the amplifier to have a greater efficiency than an analog amplifier, with less need for heat sinks or oversized components.

All of the code that [Lukasz] used is available on the project site if you’ve ever been curious about switching amplifiers. He built this more as a curiosity in order to see what kind of quality he could get out of such a small microcontroller. It sounds pretty good to us too! If you’re more into analog amplifiers, though, we have you covered there as well.

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Those Voices in Your Head Might be Lasers

What if I told you that you can get rid of your headphones and still listen to music privately, just by shooting lasers at your ears?

The trick here is something called the photoacoustic effect. When certain materials absorb light — or any electromagnetic radiation — that is either pulsed or modulated in intensity, the material will give off a sound. Sometimes not much of a sound, but a sound. This effect is useful for spectroscopy, biomedical imaging, and the study of photosynthesis. MIT researchers are using this effect to beam sound directly into people’s ears. It could lead to devices that deliver an audio message to specific people with no hardware on the receiving end. But for now, ditching those AirPods for LaserPods remains science fiction.

There are a few mechanisms that explain the photoacoustic effect, but the simple explanation is the energy causes localized heating and cooling, the material microscopically expands and contracts, and that causes pressure changes in the sample and the surrounding air. Saying pressure waves in air is just a fancy way of explaining sound.

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Listening To Mains Power, Part 2

The electricity on the power grid wherever you live in the world will now universally come to you as AC. That is to say that it will oscillate between positive and negative polarity many times every second. The frequency of 50 or 60Hz just happens to be within the frequency range for human hearing. There’s a lot more than this fundamental frequency in the spectrum on the power lines though, and to hear those additional frequencies better you’ll have to do a little bit of signal processing.

We first featured this build back when it was still in its prototyping phase, but since then it’s been completed and used successfully to find a number of anomalies on the local power grid. It takes inputs from the line, isolates them, and feeds them into MATLAB via a sound card where they can be analyzed for frequency content. It’s been completed, including a case, and there are now waterfall diagrams of “mystery” switching harmonics found with the device, plus plots of waveform variation over time. There’s also a video below that has these harmonics converted to audio so you can hear the electricity.

Since we featured it last, [David] also took some feedback from the comments on the first article and improved isolation distances on his PCB, as well as making further PCB enhancements before making the final version. If you’ve ever been curious as to what you might find on the power lines, be sure to take a look at the updates on the project’s page.

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Build Your Own Anechoic Chamber

For professional-level sound recording, you’ll need professional-level equipment. Microphones and mixing gear are the obvious necessities, as well as a good computer with the right software on it. But once you have those things covered, you’ll also need a place to record. Without a good acoustic space, you’ll have all kinds of reflections and artefacts in your sound recordings, and if you can’t rent a studio you can always build your anechoic chamber.

While it is possible to carpet the walls of a room or randomly glue egg crate foam to your walls, [Tech Ingredients] tests some homemade panels of various shapes, sizes, and materials against commercially available solutions. To do this he uses a special enclosed speaker pointed at the material, and a microphone to measure the sound reflections. The tests show promising results for the homemade acoustic-absorbing panels, at a fraction of the cost of ready-made panels.

From there, we are shown how to make and assemble these panels in order to get the best performance from them. When dealing with acoustics, even the glue used to hold everything together can change the properties of the materials. We also see a few other cost saving methods in construction that can help when building the panels themselves as well. And, while this build focuses on acoustic anechoic chambers, don’t forget that there are anechoic chambers for electromagnetic radiation that use the same principles as well.

Thanks to [jafinch78] for the tip!

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My Oscilloscope Uses Fire

If you want to visualize sound waves, you reach for your oscilloscope, right? That wasn’t an option in 1905 so physicist [Heinrich Rubens] came up with another way involving flames. [Luke Guigliano] and [Will Peterson] built one of these tubes — known as a Rubens’ tube — and will show you how you can, too. You can see a video of their results, below. Just in case a flame oscilloscope isn’t enough to attract your interest, they are driving the thing with a theremin for extra nerd points.

The guys show a short flame run and one with tall flames. The results are surprising, especially with the short flames. Of course, the time base is the length of the tube, so that limits your measurements. The tube has many gas jets along the length and with a sound source, the height of the flames correspond to the air pressure from the sound inside the tube.

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