Piezo Transducers Could Turn Displays Into Speakers

February 13, 2024 by Maya Posch 28 Comments

Will piezoelectric-based speakers replace traditional speakers over the coming years in space-constrained devices? We have definitely seen the use of piezo transducers in e.g. high-end televisions that use the display’s surface not just for the visual content, but also as a highly dynamic speaker. If you extrapolate this principle to something like smartphones, tablets and laptops the advantages are clear: piezoelectric transducers are smaller, more power efficient and do not need any holes in the enclosure. These and other advantages are what [Vineet Ganju] argues in IEEE Spectrum will push the market to adopt this new technology.

When piezoelectric transducers vibrate the display itself to create sound waves, the sound seems to come directly from the image on the screen, a much more realistic effect. (Credit: James Provost) — Piezoelectric transducers vibrate the display itself to create sound waves. (Credit: James Provost)

[Vineet] is the Vice President and General Manager of the audio business unit of Synaptics — which is one of the companies pushing for these piezoelectric transducers to be used for speaker purposes — so there is definitely some bias involved. Even so, it’s undeniable that the speakers in portable devices as well as the average flat panel TV aren’t exactly amazing, with the limited space meaning that audio quality suffers, with lows being generally absent and the resulting audio sounding ‘tinny’. Generally this is where people get external speakers for their TV, and lug portable speakers along with their laptop and other mobile devices.

For TVs, Sony has pushed for its Acoustic Surface Audio technology that uses two or three piezoelectric transducers on their OLED panels, while Samsung sticks to traditional speakers, but places lots of them around the screen with its Object Tracking Sound technology.

Sony’s technology cannot be used with LCD panels, due to the backlight being in the way, so the interesting question here is whether the piezoelectric speaker revolution proposed by [Vineet] will be limited to devices that use OLED or similar backlight-less displays?

Lo-Fi Fun: Beer Can Microphones

December 27, 2022 by Kristina Panos 16 Comments

Sometimes, you just need an easy win, right? This is one of those projects. A couple months back, I was looking at my guitars and guitar accessories and thought, it is finally time to do something with the neck I’ve had lying around for years. In trying to decide a suitable body for the slapdash guitar I was about to build, I found myself at a tractor supply store for LEGO-related reasons. (Where else are you going to get a bunch of egg cartons without eating a bunch of eggs?) I noticed that they happened to also stock ammo boxes. Bam! It’s sturdy, it opens easily, and it’s (very) roughly guitar body shaped. I happily picked one up and started scheming on the way home.

Having never built a cigar box guitar before and being of a certain vintage, I’m inclined to turn to books instead of the Internet, so I stocked up from the library. Among my early choices was Making Poor Man’s Guitars by Shane Speal, who is widely considered to be the guru on the subject. In flipping through the book, I noticed the beer can microphone project and was immediately taken by the aesthetic of some cool old 70s beer can with a 1/4″ instrument jack on the bottom, just asking for some dirty blues to be belted into it. I had to build one. Or twelve.

Continue reading “Lo-Fi Fun: Beer Can Microphones” →

Blast Chips With This BBQ Lighter Fault Injection Tool

January 29, 2022 by Dan Maloney 16 Comments

Looking to get into fault injection for your reverse engineering projects, but don’t have the cash to lay out for the necessary hardware? Fear not, for the tools to glitch a chip may be as close as the nearest barbecue grill.

If you don’t know what chip glitching is, perhaps a primer is in order. Glitching, more formally known as electromagnetic fault injection (EMFI), or simply fault injection, is a technique that uses a pulse of electromagnetic energy to induce a fault in a running microcontroller or microprocessor. If the pulse occurs at just the right time, it may force the processor to skip an instruction, leaving the system in a potentially exploitable state.

EMFI tools are commercially available — we even recently featured a kit to build your own — but [rqu]’s homebrew version is decidedly simpler and cheaper than just about anything else. It consists of a piezoelectric gas grill igniter, a little bit of enameled magnet wire, and half of a small toroidal ferrite core. The core fragment gets a few turns of wire, which then gets soldered to the terminals on the igniter. Pressing the button generates a high-voltage pulse, which gets turned into an electromagnetic pulse by the coil. There’s a video of the tool in use in the Twitter thread, showing it easily glitching a PIC running a simple loop program.

To be sure, a tool as simple as this won’t do the trick in every situation, but it’s a cheap way to start exploring the potential of fault injection.

Thanks to [Jonas] for the tip.

An acousto-optic tunable filter and laser

Acousto-Optic Filter Uses Sound To Bend Light

September 10, 2021 by Dan Maloney 17 Comments

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” →

Buzzer Does Input And Output

January 25, 2021 by Al Williams 2 Comments

Piezo elements have the useful property of being bidirectional; that is they can move when you apply electricity to them, but they can also generate electricity when you move them. [Carl] takes advantage of this fact to make buttons that can provide haptic feedback. You can see a video of his efforts below the break.

He made two versions of the buttons. One uses a 3D printed housing and the other used a 3D printed spacer in a sandwich configuration. It took a few tries to get it right, as you’ll see. The elements take and produce relatively high voltages, so the bulk of the work was adapting the voltages back and forth. In fact, he even managed to fry his CPU chip with some of the higher voltages involved.

We’d probably look for an easier way to sense the button push, since it seems like a good bit of circuitry just to do that. But the whole circuit provides an input button, haptic feedback, and the option of using the buzzer as a buzzer, so at least it is relatively economical if you need all of those features.

Continue reading “Buzzer Does Input And Output” →

Microcontroller Studies The Blade

February 2, 2020 by Bryan Cockfield 8 Comments

Kendo, a Japanese martial art, is practiced with a special sword. It’s not a particularly sharp sword, though, since the “blade” is essentially a length of bamboo. For this reason, Kendo practitioners must rely on correct form and technique in order to make sure their practice is as effective as possible, and Cornell students [Iman] and [Weichen] have made a Kendo trainer that helps the swordsmen in their art.

The core of the project is a PIC32 microcontroller hooked up to a set of three piezoelectric sensors and a LSM9DS1 inertial module. The three piezoelectric sensors are attached to a helmet and the inertial module to the sword, and the sensors work together to determine both the location of the strike and whether or not it had enough strength to be considered a “good” strike (the rules of Kendo are beyond the scope of this article). The trainer can then calculate all of the information and provide feedback to the user on a small screen.

While martial-arts related builds seem to be relatively rare, we did find a similar project from back in 2011 called the Virtual Sensei which used a then-popular Kinect in order to track movements. This PIC32-based project, though, seems to be a little more thorough by including the strength of the strike in the information the computer uses, and is probably less expensive to boot!

Continue reading “Microcontroller Studies The Blade” →

Piezoelectric Antennas For Very, Very Low Frequencies

April 16, 2019 by Brian Benchoff 40 Comments

If you want to talk about antennas, the amateur radio community has you covered, with one glaring exception. Very low frequency and Extremely Low Frequency radio isn’t practiced very much, ultimately because it’s impractical and you simply can’t transmit much information when your carrier frequency is measured in tens of Hertz. There is more information on Extremely Low Frequency radio in Michael Crichton’s Sphere than there is in the normal parts of the Internet. Now there might be an easier way to play with VLF radiation, thanks to developers at the National Accelerator Laboratory. They’ve developed a piezoelectric transmitter for very long wavelengths.

Instead of pushing pixies through an antenna, this antenna uses a rod-shaped crystal of lithium niobate, a piezoelectric material. An AC voltage is applied to the rod makes it vibrate, and this triggers an oscillating electric current flow that’s emitted as VLF radiation. The key is that it’s these soundwaves bouncing around that define the resonant frequency, and the speed of sound in lithium niobate is a lot slower than the speed of light, but they’re translated into electric signals because of its piezoelectricity. For contrast, if this were a wire quarter-wave antenna it would be tens of kilometers long.

The application for this sort of antenna is ideally for where regular radio doesn’t work. Radio doesn’t work underwater, but nuclear subs trail an antenna out of the back to receive messages using Extremely Low Frequency radio. A walkie talkie doesn’t work in a mine, and this could potentially be used there. There is a patent for this piezoelectric antenna, so if anyone knows of a source of lithium niobate, put a link in the comments.

We’ve seen this trick before to make small antennas even smaller, but this is the first time we’ve seen it used in the VLF band, where it’s arguably even more impressive.