Feasibility of controlling 24 audio exciters independently with Arduino

[Robinvh99]

Hi Everyone and thanks for reading

Currently, we have a prototype in which we are using 24 basic DC vibrational motors to create vibrational patterns over a large surface. However, as we need to speed up the patterns, and DC motors have a 'speeding up' time which is quite extensive, we went looking for other options. What we ended up with is a possibility using what I think is commonly called 'audio exciters', which to my knowledge are basically small 'speakers' that can create vibrations.

This website (sorry for linking external) shows some of the tectonic exciters that we are considering.

However, when looking into this, it seemed like an Arduino can only pass one frequency, thus either allowing only 1 audio exciter to be controlled, or all 24 to be controlled, but always emitting similar behavior (so passing the same frequency and amplitude to all motors).

My question is whether any of you knows whether it is possible to control multiple audio exciters independently with one Arduino, and how that possibly would work? More generally, the problem comes (in our eyes) down to being able to 'send' waveforms with variable frequencies and amplitudes as inputs to multiple audio exciters.

Any hardware needed which is relatively small (final product should be somewhat mobile), would be no problem to add.

Lots of thanks in advance!

[johnwasser]

it seemed like an Arduino can only pass one frequency

Perhaps someone pointed you at the built-in 'tone()' function? You will have to use a different method to get 24 channels.

What range of frequencies do you need? How accurate do the frequencies have to be?

[Robinvh99]

Hi John, thanks for your time and your questions.

We only really need 2 frequencies, being 60Hz and 300Hz. It will most likely not be problematic if the frequency is a few percent off, so 295Hz, or maybe even 290 although that would be a limit, would most likely not be a problem.

We do need varying amplitudes.

Hope this helps!

[TomGeorge]

Hi,
Will the exciters be generating vibrations all the time?
That is will your vibrators have
2 states, 60Hz or 300Hz?
OR
3 states, 60Hz, 300Hz and 0Hz?

Tom...
PS, External linking like that is encouraged for product or component data so it doesn't make the posting too long.
Sample of OPs exciters.

[Robinvh99]

Hi Tom! Thanks for the question

Our vibrators will have 3 states, sorry for not clarifying this earlier. So 0Hz, 60Hz and 300Hz.
As explained earlier, there will be 24 of them, and occasionally, a subset of those tectonic/audio exciters will be vibrating.

-Robin

[Etemenanki]

Well, first of all, do you need a simple square wave or a sine wave driving for the exciters ? ( that, yes, are basically just speakers without the cone) ... asking cause you mentioned vibrational patterns, that usually are obtained using sinewaves ... also vibrating motors mainly produces an equivalent of a sine wave force, mechanically speaking ... so, is influent if the vibration is crude square wave, for your application ? ...

Second, do you need also an amplitude control for the strenght of the vibrations ?

Sorry, not for put my nose in your business, but for what is needed all this ? ... test stress ? ... medics ? ... other ?

For have the more possible control for all your parameters (and cause you say you need only 2 frequencies) you can also think of the possibility to use external oscillators with audio amplifiers modules that drives the "speakers", and use Arduino for control on/off and/or intensity of them (also each individual speaker, if needed, just a bit more of circuitry is needed, but is possible)

By the way, have you also considered what is the power (as mechanical strenght) of the vibrations you need to apply ? ... are those speakers strong enough ?

[alto777]

Those transducers drop off in frequency response below 200, at least the few I looked at.

They handle 5 or ten watts of audio power, at least the few I looked at.

What audio power do you need to deliver?

It seems like each transducer needs an audio power amplifier.

Maybe 24 small audio amplifiers, two sources for 300 and 60 Hz signals fed through 48 digital potentiometers controlling the input amplitude to each transducer.

Or a digital switch at each amplifier selecting 300 or 60, and then a digital pot fir amplitude.

a7

[Robinvh99]

Well, first of all, do you need a simple square wave or a sine wave driving for the exciters ?

Most likely, square waves. Both are probably possible, don't think it matters too much for us.

Second, do you need also an amplitude control for the strenght of the vibrations ?

Yes we need to be able to control amplitude for the strength of the vibration.

Sorry, not for put my nose in your business, but for what is needed all this ?

No worries! At this point we are trying to replicate the findings that a scientific paper has published in the area of human augmentation on the ability of humans to understand language through vibrational patterns. We are a group of students (still looking for an electrical engineer as you might imagine) from Eindhoven University (Netherlands). So research purposes, but we hope to go further into research in human augmentation Also, if it would be of any issue for people, there is no 'profit' linked to any of this, its just research because we are invested in the topic and wanna push the research field further. The paper in question

So why go through this trouble when there is research? There prototype consisted of an 1100 multichannel amplifier which is big and chunky. We are trying to get a prototype which is wearable and transportable. Hope this helps to clarify.

By the way, have you also considered what is the power (as mechanical strenght) of the vibrations you need to apply ? ... are those speakers strong enough ?

As we are replicating the findings of a paper, we are currently not worrying about the strength of the speakers.

Those transducers drop off in frequency response below 200, at least the few I looked at.

See response above. As we are replicating a paper, the exciters possibilities should be fine.

What audio power do you need to deliver?

Not exactly sure? Also not completely sure what you mean? The paper specified a range of -32dB to -45dB relative to the maximum output of the exciters if that helps you? Think the max of those exciters is like 4W.

3 states, 60Hz, 300Hz and 0Hz?

Coming back on this, yes for this prototype this would be enough. However, if we can come up with a possibility which would allow us to scale into more complicated stuff in the future that would be greatly preferred. Preferably we would be able to just control 24 exciters separately on all options. We would also not care too much on bigger parts etc too much. We could research later on how to make everything as small as possible. We are now prioritizing just building a good prototype on this.
Huge thanks for helping out in any way. I also see now that my initial question was inherently vague and you guys have already helped me a lot by just asking the right questions!

[alto777]

Going as far as your link takes me without trying harder, it looks like the experiment in the paper involved very small exciters, an array of 24 to fit on a person's forearm.

Much smaller transducers… would need much less power. I'm thinking like old fashioned earbud speakers, a coil and a magnet and a diaphragm.

But you said a large surface. Are you nevertheless still talking about a device for humans to receive numbers and letters through vibrational patterns sensed by a forearm?

Or?

a7

[Robinvh99]

You are completely correct that the exciters are smaller than the one linked.. Some on that page are smaller, but the one later shown in the picture is much bigger. The correct one is this one.

But you said a large surface. Are you nevertheless still talking about a device for humans to receive numbers and letters through vibrational patterns sensed by a forearm?

yes. I considered the forearm to be a large surface

[Etemenanki]

Uhm ... 32-33 mm diameter ..... considering also the connection part ..... also bending the tabs and placing them diagonally, i doubt they can be kept at distances less than 40mm one to other (the center of them, i mean) ..... supposing you are placing them in 8x3 array, this means they will cover around 12x32cm space ..... or in 6x4 pattern, 16x24cm space ..... do you plan to wrap them around a forearm ? .....

As alternative comes in mind only piezoelectric transducers, but they need to be well insulated (requires higher voltages, so also final transformers after the amplifiers, also if small is more space) ..... or also piezoplastic ones (PVDF), but high costs are not a good thing, and still need insulation (nothing that a Kapton tape layer cant handle, anyway) ..... other than this, the only other alternative that come me in mind for find smaller ones, is to get a bunch of cheap Chinese $2 in-ear earphones from Aliexpress or similar sites and massacre carefully dismantle (:D) them for the mini-loudspeakers inside .....

[alto777]

Yes, I thought also the transducer still seems large.

Also, aren't those drivers meant to be held in contact with something that then moves air for sound? Like bolted to a table or glued to an amusement card.

So are you sure that an arm can "hear" even one exiter just held in place?

Can you share more about your DC motor prototype? How are those motors controlled, is there anything there that would inform controlling the transducers in their stead?

a7

[Etemenanki]

Where there is the ring of 3M adhesive, is the end of the coil holder, the part that usually is glued to the cone ... probably the adesive ring is planned for be glued on the vibrating surface, but you still can feel it vibrate if you keep it on the skin ...

Anyway, i think also different transducers can work, cause (as far as i understood from the OP posts) the item is "wearable" so the vibrations are sensed with skin contact ...

but, about motors, there are disk motors (coin motors ? ) for cellphone vibrations that are around 10mm, also 8mm if smaller needed, but that way cannot be used specific frequencies, that is the request of the OP ... i mean, is not possible to set them to vibrate at specific frequency, they are just 2-coils DC motors with their own controller inside ...

[alto777]

Yes, it is this alleged "surface" that has gone unspecified.

I asked about the motors because I want to know how those were rigged and controlled in the original prototype. Call it curiosity if you need to. I thought it might inform the development of the sonic stimulator mechanically and electrically. And code wise maybe. Curious.

I mentioned the ear bud "speaker", it seems like a better match in terms of size and my current apprehension of the desired outcome.

a7

[Etemenanki]

Yes, i also considered the earpieces speakers ... the possible problem is that they have a really light and thin membrane, compared with the mass of the rest of the speaker, so is probably difficult to "feel" the vibration (after all, using them we feel almost no vibration in ear, sound apart) ... maybe glueing some plastic in the center of the coil for make it weight more ...

There is also another possible alternative but need to be tested ... actually on market are available the speakers of a lot of cellphone models at low prices, and some of them are really powerful, for the size they have ... maybe using a square model with an exposed frontal membrane (like this one or similars https://ae01.alicdn.com/kf/H8455adc41111468c99e68719e3ce45e2F.jpg ) and glueing a small piece of plastic in the center of the diaphragm (so it come at the same height of the border and touch the skin), may work better than earphones from earbuds ... and they are small too ... but need to be tested ...

[Robinvh99]

So are you sure that an arm can "hear" even one exiter just held in place?

As they are the exact same as are used in the paper, we wanted to try these first.

Would these others that have been suggested make it easier to connect it to an arduino and control them independently? The biggest question we currently have is how we would/could wire them up.