Hacklet 103 – Piezo Projects

The piezoelectric effect is simple in its rules: Apply mechanical stress to a material and you generate an electric charge. The inverse is also true: Apply a voltage to a material, and it changes shape. This doesn’t work for everything, though. Only certain materials like crystals, some ceramics, and bone have piezoelectric properties. The piezoelectric effect is used quite a bit in electronics, so it’s no surprise that plenty of hacker projects explore this physical phenomena. This week’s Hacklet is all about some of the best projects utilizing the piezoelectric effect on Hackaday.io!

strumWe start with [miro2424] and StrumPad. Strumpad lets you play a MIDI instrument by strumming, just like a guitar. A music keyboard acts as the guitar fretboard here – keys can be pressed to choose notes, but no sound is generated. When the strumpad is strummed, six copper strips act as capacitive sensors. Touching the strips determines which notes will be played. A piezo disc hiding below the circuit board detects how hard the notes have been strummed or tapped. The ATmega328 running the strumpad then passes the velocity and note-on MIDI messages on to a synth.

stmNext up is [Dan Berard] with Scanning Tunneling Microscope. Inspired by a project from [John Alexander], [Dan] created his own Scanning Tunneling Microscope (STM). The key to an instrument like this is precise movement. [Dan] achieves that by using a normal piezo disk. These disks are used as speakers and buzzers in everything from smoke detectors to greeting cards, so they’re common and cheap. [Dan] cut his piezo disk electrode into quadrants. Carefully controlling the voltage applied to the quadrants allows [Dan] to move his STM tip in X, Y, and Z. Incredibly, this microscope is able to create images at the atomic scale.

touchboard[Thatcher Chamberlin] is next with Low-Cost Touchscreen Anywhere. [Thatcher] used a trio of Piezo disks to make any flat surface touch sensitive. The three sensors are placed at 3 corners of a rectangle. Touches with the rectangle will create vibrations in the surface that are transmitted to the piezo sensors. By measuring the vibration time of arrival, it should be possible to determine where the surface was touched. This kind of measurement requires a decent processor, so [Thatcher] is using the ARM Cortex-M0 in NXP’s LPC1114FN28. Initial tests were promising, but we haven’t heard much from [Thatcher] on this project. If you see him online, tell him to hurry up! We’re hoping to turn our parking lot into a giant electronic chess board!

contFinally, we have [Jose Ignacio Romero] with Low Power Continuity Tester. [Jose] used a Piezo element in a slightly more mundane way – as a buzzer. Who needs a whole multimeter when you’re just trying to check continuity on a few circuits? This continuity tester uses a PIC12LF1571 processor to find open and short circuits. The 5 10 bit ADC in the PIC is plenty of resolution for this sort of tester. In fact, [Jose] even included a diode test, which emits a short beep if the leads are placed across a working diode. The PIC processor uses so little power that this tester should run for around 800 hours on a CR2032 watch battery.

 

If you want to see more piezo projects check out our brand new piezo projects list! If I missed your project, don’t get buzzed! Drop me a message on Hackaday.io, and I’ll add it to the list. That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!

Harvard’s Microrobotic Lab Sinks RoboBees and Claims it was on Purpose

What do you call tiny flying robots that undoubtedly emit a buzzing noise as they pass by? Mosquitoes are universally hated, as are wasps, so the logical name is RoboBees.

The Wyss Institute for Biologically Inspired Engineering at Harvard University has been cooking up these extremely impressive tiny robots in their Microrobotics lab. The swarms use piezoelectric actuators to produce the mechanical force to drive the wings, which can be independently controlled.This isn’t the first time we’ve looked in on the Robobees, but the most recent news revealed the ability to swim, and dive (term used generously) into water.

This may not sound like much, but previously the robots lacked the ability to break the surface tension of water. To sink, the wings need a coating of surfactant. Once submerged, the bots lack the ability to transition back from water to air. But we won’t be surprised to see that ability added as a feature while the scope of the project continues to creep. So yes, you can jump into water to escape bees but not to escape Robobees.

Diving isn’t the only wonder to behold. The ‘head’ of the RoboBee is utterly fascinating. It’s constructed by folding the PCB into a pyramid like structure, 4 sides of the head include a photo-transistor covered by a diffused lens which the bot uses for self positioning by sensing changes between the bright light of the sky and absence thereof below the horizon. This concept is taken directly from biological self-righting systems found on the head of most insects, however Harvard’s version has one more sensor than the stock 3 seen on insects. Take that, nature!

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Measuring Heart Rate With A Piezo

Look around for heart rate sensors that interface easily to microcontrollers, and you’ll come up with a few projects that use LEDs and other microcontrollers to do the dirty work of filtering out pulses in a wash of light.

[Thomas] was working on a project that detects if water is flowing through a pipe with a few piezoelectric sensors. Out of curiosity, he taped the sensor to his finger, and to everyone’s surprise, the values his microcontroller were spitting out were an extremely noise-free version of his heart rate.

The piezo in question is a standard, off the shelf module, and adding this to a microcontroller is as easy as putting the piezo on an analog pin. From there, it’s just averaging measurements and extracting a heartbeat from the data.

It’s a much simpler solution to measuring a heart rate, and since two people haven’t heard of this technique, it’s likely a lot more people haven’t heard of this technique either. If you’re looking for an entry to The Hackaday Prize, this would be a great jumping off point for anything in either the fitness or medical domains.

Turn a PC on with a Knock and an ATTiny

knockAttiny

Pressing the power button on your computer usually isn’t too much trouble, unless your computer is stored away somewhere hard to reach. [Joonas] has been hard at work on a solution that would also impress his friends, building a knock sensor to turn on his PC.

For around $10 in parts he put together an ATTiny45 that emulates a PS/2 device, which takes advantage of his computer’s ability to boot upon receiving PS/2 input. The build uses a Piezo buzzer and a 1M Ohm resistor as a knock sensor exactly as the official Arduino tutorial demonstrates, and one of those PS/2-to-USB adapters that are most likely lurking in the back corner of every drawer in your office.

[Joonas] used AVRweb to disable the 8X clock divider so there’d be enough clock cycles for PS/2 communication, then loaded some test code to make sure the vibrations were being detected correctly. You can check out his Github for the final code here, and stick around after the break for a quick video demo. Then check out a similar hack with [Mathieu’s] home automation knock sensor.

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Storing 32 bits of data in a piece of glass

After finding an old piezoelectric delay line in an old TV, [Mike] decided to figure out how it works and in the process stored his name in sound waves reflecting inside a piece of glass

[Mike] was intrigued by these old-fashioned delay lines after watching [Dave] from EEVblog’s teardown of an circa 1985 camcorder. [Dave] found a piezoelectric delay line in his camcorder – a device that is able to store digital data by sending a sound wave into a glass plate, letting the sound wave bounce through the plate. and picking up the sound on the other end. It’s actually not too dissimilar to a mercury delay line used in the earliest computers.

After sending a pulse through his piezoelectric delay line, [Mike] picked up an echo almost exactly 64 microseconds later. After hooking up a simple circuit constructed out of a 74-series chip, [Mike] found he could ‘loop’ the delay line and keep a pulse going for up to 3 milliseconds.

Three milliseconds isn’t much, but by injecting serial data into the delay line, [Mike] was able to spell out his name in binary, as seen above. It’s just 32 bits stored for a fraction of a second, making it a very volatile, low-capacity memory, but functionally equivalent to the old mercury delay lines of yore.

It’s certainly not what [Mike] or [Dave]’s delay line was designed to do; these video delay lines were used to hold the previous line of video for a form of error correction. Outside [Mike]’s workbench and a few museums, though, you won’t see a delay line used as a form of computer memory. A very cool build and an awesome history lesson, and we thank [Mike] for that.

biological-inspired robotic eye movements

Researchers at Georgia Tech have developed a biologically inspired system to control cameras on board robots that simulate the Saccadic optokinetic system of the human eye. Its similarity to the muscular system of the human eye is uncanny.

Joshua Schultz, a Ph.D candidate, says that this system has been made possible in part to piezoelectric cellular actuator technology. Thanks to the actuators developed in their laboratory it is now possible to capture many of the characteristics associated with muscles of the human eye and its cellular structure.

The expectation is that the piezoelectric system could be used for future MRI-based surgery, furthering our ability to research and rehabilitate the human eye.

[via engadget]

Electronic recorder conversion

As we wrote the title to this feature we can see why [Jeff Ledger] calls it an electronic flute and not a recorder; this is a musical instrument and not something for archiving audio. Confusion aside, we’re all familiar with these plastic ‘musical’ instruments. Many elementary schools in our area require students to buy one as part of music class. So it shouldn’t be hard to find one if you want to try this for yourself (heck, [Jeff] grabbed his a the dollar store).

Basically, he’s replaced the finger holes with momentary press switches, then uses a Propeller dev board to turn the button presses into music. It’s simple and quick, but what does it for us is the breath actuator. Sure, you can set this up to play whenever a button is depressed, but [Jeff] went that extra mile and added a piezoelectric element to the bottom. When you blow through the instrument it flexes slightly, generating a tiny current that can be measured by the microcontroller. Check out the short clip after the break.

Do a little more work and you could turn this into some type of musical game controller. We’re thinking Zelda!

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