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. 3v Dc Buzzer
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.
The last time we saw a piezo speaker detecting something it was looking for knocks on a door. If you want to know more about how transducers like this work, you’ll enjoy this video.
I’d built a project for my brothers track car about 4 years ago that detects engine knocking. It displayed the scale of the knock sensor on a number of LEDs (about 12 green, yellow & red all up) as well as tones via a headphone jack. This was used for fine tuning the engine in his workshop & as a dash display during test drives.
At the time of building this my brother and I lived 6 hours drive apart, building it with the car present wasn’t an option. So I opted to use a piezo buzzer like that in the article to get the project off the ground.
Car knock sensors are essentially a piezoelectric disk or ring built to create voltage at a very specific vibrating frequency. This frequency is that which knocking/pinging/detonating makes through the engine block.
Knowing the curve and the voltage at the resonance point of the knock sensor meant I could build a reliable scale for the LED to Human eyeball connectivity.
Sadly I have no video of the final device, but I do have a very early video I made for my brother just when I was getting things started. The final device also did not stay in that old boost gauge, though I have that lying around somewhere.
I must say though, I love the idea of using them as a button with feedback. I might have to implement the idea in something myself one day. Or maybe I could log when my cat is feeding, her stainless steel bowl would be purrfect for capturing vibrations at snack time.
[youtube https://www.youtube.com/watch?v=Jo_OMDANjeU&w=560&h=315%5D
I’m still not sure I’d fully trust the voltage to stay where I want it at those voltages and frequencies. Pizeo electric materials and drivers can give you a bit of a zap if you’re not careful. Stacking them on top of each other, with little stand offs or adding little levers to them, can be a good way to increase the range of movement and/or output force/output voltage.
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