Making piezoelectric actuators for skin feedback

Hi all,

First time poster, was wondering if anyone knew anything about piezoelectric actuators and how to make them. I ordered myself a sheet of Velostat and made a pressure sensor as seems to be the rage with this stuff, and that works great, but I can't find anyone who uses it in the other direction, that is, as an actuator.

I've given it as much as my power supply will put out, 15V, but the velostat doesn't budge. PWM from an arduino doesn't do anything. And I can't find anything about how to build one of these things, just pre-built (and very expensive) products.

Does anyone know how to make them and what you need to power them?

Thanking you in advance! Loren

I don't think Velostat is piezoelectric... It might have a variable resistance...

And, I've never actually seen movement from a piezo transducer. I've heard sound but that's not enough movement to see. I'm not saying it can't be done, but I've never seen it. (You can see a woofer move, but they don't make piezo woofers.)

I would guess it takes high voltage to get movement you can see... Maybe thousands of volts. A piezo transducer can also generate high-voltages... They use them to generate sparks... Velostat isn't supposed to do that!

I'm not sure if Velostat would work at all. I've never heard of Velostat being used as a speaker/tweeter, but if it can make a sound it's obviously vibrating/moving.

Stickytape Sensors. These sensors measure pressure and can also be designed and placed to measure bend. They work on the simple principal that Velostat reacts to pressure with a decrease in electrical - resistance.

Piezo actuators are sometimes used on electron microscope stages to produce very tiny movements.

Microns.

Not very much

Alan

Google "Piezo braille cell". They move quite a bit, but need ~200volt drive. Leo..

Yeah I started to suspect that velostat might not do the trick. Thanks for confirming my suspicions everyone. Now that I look again, people do call velostat piezoresistive. It’s still excellent for making pressure and bend sensors.

The braille cell is particularly interesting, but yeah way too high voltage for my purpose…

As a followup, does anyone know of any good skin-contactable feedback devices for arduinos? I have a flat asymmetrically loaded motor that runs at low voltage, but it’s still quite expensive to get a lot of them and I kind of want to make it myself if possible.
What about a very small AC or PWM signal to create a tingling sensation? Does anyone know what sort of voltage/current range is detectable/safe? Or is that too unstable due to the variable contact with the skin? Too high power for a portable device as well perhaps?

I may post this in a new thread so it’s more visible, but I’d love to get your feedback especially. Thanks!

Does anyone know of any good skin-contactable feedback devices for arduino?

I have a flat asymmetrically loaded motor that runs at low voltage, but it's still quite expensive to get a lot of them and I kind of want to make it myself if possible.

What about a very small AC or PWM signal to create a tingling sensation? Does anyone know what sort of voltage/current range is detectable/safe? Or is that too unstable due to the variable contact with the skin? Too high power for a portable device as well perhaps?

Thanking you in advance Loren

What do you consider “quite expensive” I see a 10 pack of pager motors on eBay for $4.34 USD w/ free shipping.

Hmm that’s not too bad, I’ll have better look for those. The asymmetrically loaded motor I have cost about $2

Go with the motors. Using TENS type shock will pose more liability concerns than it's worth.

Here it is: https://www.ebay.com/itm/322617231341 You might find a better price with some searching, especially if you want more quantity than 10. If you need less than 10 the price is a little more but still very reasonable. You could probably save a little by buying on aliexpress.com. I've found the customer service tends to be worse on that site when there's a problem with the order but the majority of my orders had no problems.

I wonder if a small speaker element would do the trick. The electro-mechanical kind [coil of wire around a permanent magnet]. They are, essentially, short throw linear actuators, and I’ve seen ones that are small and quite flat. So, I guess it would be a matter of whether or not they have enough mass & and enough low frequency response, to create the required type, and level of sensation.

Thinking out loud: First, try it as a normal speaker. But, if that doesn’t produce the desired effect, then perhaps if mounted from the diaphragm [probably a mylar-ish diaphragm is indicated], the housing/magnet would, having the greatest freedom of movement, be more likely to produce greater action, and thus, having more mass, be more likely to create the desired sensation. So, perhaps the diaphragm is, somehow, extended out to contact the skin, or some sort of band that is wrapped around a limb. Perhaps a ring, made from slicing a tube, could be glued to the diaphragm. Then, the other side of the ring made to contact the skin, or the mounting apparatus.

BUT, encumbering the movement of the diaphragm might lower the impedance of the speaker to the point where normal drive would burn it out. So, some experimentation would, probably, be needed. Also, if this is ultimately, to go into production, then realize that using a device outside of it’s published parameters, will, likely, void any support from the manufacturer – unless you actually contact the manufacturer and work out some sort of arrangement.

Examples:

Along those lines, piezo disks could be a possibility. They are available in a variety of sizes down to 12 mm diameter, more low profile than the motor or speaker, and the price is super good if you buy them in quantity: https://www.ebay.com/itm/153021728672 1/10th the price of the motors.

The common term for this is "haptic feedback". You might find some more ideas with some searching on that term.

I just found where I bought the vibrating motor before: https://boutique.semageek.com/fr/909-mini-moteur-vibreur-disque.html
AliExpress and eBay both have much cheaper options. You’re quite right, pert.

I’ll check out haptic feedback and the piezo disks, they seem like a good research avenue. I imagine the piezo disks pressed against the skin wouldn’t produce sound anymore, but still produce a slight sensation…

Also the speaker option could be interesting too in the same way. I imagine it would disable the audible aspect just like the piezo disks when pressed against the skin. I guess the challenge, as you say ReverseEMF, is that you risk overloading the speaker if it is too firmly attached. I have some small speakers around somewhere like what you’ve linked. I’ll have a go!

The motors and speakers certainly seem like the easiest solution, though TENS is interesting still since it’s only for personal use. A quick google told me that it’s probably a lot more effort than it’s worth to setup. Thanks for the acronym though, INTP!

I happen to have a board with a 12 mm and a 32 mm piezo disk wired to it sitting on my desk. I just tested it and with a 5 V "full swing" direct drive from the ATmega328P the vibration is definitely noticeable with the 32 mm piezo disk and only barely noticeable with the 12 mm disk. Although the frequency I used was sub-sonic (10 Hz) you can hear a distinctive clicking noise with the 32 mm disk, even when pressed firmly against the skin, probably about the same sound level as the pager motor. The noise from the 12 mm disk is inaudible when pressed against the skin.

You would likely get more noticeable vibration and also louder clicks with a higher drive voltage.

pert: I happen to have a board with a 12 mm and a 32 mm piezo disk wired to it sitting on my desk. I just tested it and with a 5 V "full swing" direct drive from the ATmega328P the vibration is definitely noticeable with the 32 mm piezo disk and only barely noticeable with the 12 mm disk. Although the frequency I used was sub-sonic (10 Hz) you can hear a distinctive clicking noise with the 32 mm disk, even when pressed firmly against the skin, probably about the same sound level as the pager motor. The noise from the 12 mm disk is inaudible when pressed against the skin.

You would likely get more noticeable vibration and also louder clicks with a higher drive voltage.

Yeah, and I would, also, try a higher frequency. More like 50 to 100 Hz.

50 Hz is more noticeable than 10 Hz. At frequencies much above that it starts getting less noticeable.

I found that pulsing the frequency made it more noticeable. 150 ms pulses of 60 Hz seems to be pretty good.

The noise of the buzzer is a bit more annoying at higher frequencies.

Google "vibration speaker" or "contact speaker" or "bass shaker". The bare driver. Not sure how small they make them. Leo..