Vibration device advice requested

I need at least 2 vibration sources that can vibrate in the range of 100hz to 200hz and be able to be turned off and on between 4 and 40 times per second. For a different project is used 2 Solid State Relays to provide the on/off switching. That should work on this project. What I am at a lost is to source a device that can output the 100hz to 200hz vibration. My search lead me to Tetonic Compact Audio Exciter, Micro Speakers from Regal, and adafruit Speakers. Input on better or just alternative devices would be appreciated. BTY, I need to "mount" the device on a Velcro strip so that they can be placed on the arm, so not too heavy nor too hot in temperature.

I haven't yet researched how to drive any of these devices at the required frequency. I would expect a simple alternating current would suffice.

Those devices will all require extra electronics to drive them, for example an audio amplifier, and a separate power supply.

The Arduino may not be used to directly drive devices that use more than a few dozen milliwatts of power.

Have you considered mini disk vibrating motors? Note that even these tiny devices require a transistor driver.

Or pager motors?

FYI, modulating a 100Hz frequency with a 40Hz frequency will set up intermodulation products, "beat frequencies".

Perhaps is didn't provide an accurate description of the device I want to build. Pick a vibration frequency between 100hz and 200hz. Lets say 180hz. There are two outputs vibrators labeled 'A' and 'B'. When A is on, B will be off and when A is off, B will be on. A get turned on and off 5 times per second.

How does this create "beat frequencies"?

But I need to be able to tune the output to somewhere between 100hz and 200hz. I haven't yet established the "correct" frequency. My understanding of they 'coin' size vibrators is that they have a somewhat fixed frequency or is that my misunderstanding of this technology?

The tiny vibrators can be tuned by adjusting the supply voltage. You would have to experiment to determine the tuning range.

As mentioned above, you will never get just one "correct" frequency out of the device you have described so far. For 100 Hz turned on and off at 40 Hz, you will get 60 Hz and 140 Hz as the most prominent sidebands, as well as the simple integer harmonics of all those frequencies.

Apparently you did not. :worried:

The point is that it is not practical - or indeed, theoretically meaningful - to switch a particular frequency at a rate comparable to that frequency.

The act of switching or "modulating" a frequency alters the frequency such that it is no longer a single frequency. In addition, switching "on" and "off" implies that you are modulating with a square wave, which itself is not a single frequency but a complete spectrum of frequencies.

Now either you comprehend this or you do not. To make any progress, you really need to explain the complete purpose of your project which is so far, an "XY Problem". :roll_eyes:

...* To make any progress, you really need to explain the complete purpose of your project*...

I have a condition called Essential Tremors that affects my forearms and hands. My dominate tremor is a FPS: Forearm Pronation Supination which in simple terms is the rotation of the forearm about 20° clockwise followed by about 20° anti-clockwise at a frequency of about 5hz. I can no longer write in cursive, using a mouse is a challenge, and soldering might be impossible. Aside from brain surgery (DBS) 80%-90% and Focused Ultrasound 85% where the cook part of your brain, most other treatments work for 50% of ET population and/or are less that 50% effective in reducing tremors.

There are two promising treatments for FPS tremors. Firstly there is Electrical stimulation of the median-radial nerve near the wrist. Success rate slightly less than 50%. I am in the middle of building this type of unit. Secondly there is some preliminary work indicating that a similar stimulation strategy of mechanical stimulation of the Pronator Teres - Supinator muscles located near the elbow may provide some relief.

Both of these techniques rely on alternating the stimulation between two points on the forearm at the frequency of the tremor. Current stats of tremor frequency of ET's is in the range of 5hz-12hz.

tl/dr The problem is to provide a mechanical stimulation of the Pronator Teres - Supinator muscles at a frequency in the range of 100hz - 200hz and to alternate the target stimulation between these two muscles at a frequency in the range of 5hz to 12hz.

AMA (Ask Me Anythig)

My impression of your description is that people tried some forms of mechanical stimulation, and it may have helped in some cases.

So, if it works at all, the exact treatment details may not be very important, but in case they are, surely many trials with many people would be required to discover a "best recipe".

It seems premature to worry about particular frequencies. And, what about vibration amplitude?

What does this mean? Are there two vibrators?

It was a graduate research project in Japan. They showed that mechanical stimulation of the two muscles can demonstrate pronation/supination movements. Full disclosure: they only tested "healthy" subjects.

I agree regarding the details which suggests try out a couple of coin vibrators and see if there is a measurable result. The 100hz-200hz range can wait until prototype #2 or later.

I hear what you are saying regarding the "best recipe". My research on ETs indicates that the "best recipe" will be different for each individual and need to be tuned in to be effective.

I don't have access to many people (yet). I'm the only guinea pig available for now.

Yes. I every scientific paper I have read regarding the treatment of Essential Tremors by either electrical or mechanical stimulation uses two points of application. In all cases the alternation of application points is at the frequency of the tremor.

OK, so the exact frequency of the stimulation is completely arbitrary, so we can ignore all the concerns about whether it is a pure frequency, accurate or consistent.

I don't know offhand what the speed of these little vibration motors is - I have a pack of them somewhere so if I could only find them I might be able to check it out - and since they have inertia, I don't know how effectively you can start and stop them many times per second but by all means give it a try - they are pretty inexpensive.

The obvious alternative is to use miniature loudspeaker inserts and the "tone" function in the Arduino - you will need amplifiers to deliver sufficient power.

Because I need to switch the stimulation between point A and point B, the response time of these motors is critical. Having deep dived into the specs I find that I can source a motor which has a fast, 10ms rise time, but all the motors I spec'ed took far to long to stop vibrating. This is a roadblock to even testing this type of motor.

Piezoelectric actuators seem to have fast enough response times, but the cost may put these devices beyond my budget at present.

Piezoelectric devices are generally used for much higher frequencies. You want an electrodynamic device such as a miniature loudspeaker.

To get a fast rise time the motor will need (relatively) a lot of power to accelerate it against its moment of inertia.

Rotational kinetic energy can be expressed as: Erotational=0.5 I ω * ω where ω is the angular velocity and Iis the moment of inertia around the axis of rotation.

Perhaps depending on the type you can use regenerative braking to stop it just as quickly?

Does the research indicate the intensity needed - or does it just have to be perceptible?

The paper did not address this issue. "(the) contact force between the vibrator and the skin was kept at 3 N in all experiments."

"A small brushless motor (Maxon Motor, ECXSP16M) is installed on the vibrator housing. The rotation shaft with an eccentricity of 1.5 mm is attached to the motor output shaft, which generates the vibration stimulation. The eccentricity acts as a crank and determines the amplitude of the vibration stimulation (3 mm). This vibrator can operate at frequencies that range from 20 Hz to 250 Hz, and the frequency of vibration stimulation is adjusted by controlling the angular velocity of the motor. A hall sensor is built in the vibrator to measure the time for one rotation of the motor and obtain the frequency of the vibrator. The vibrator is attached to the forearm using a flexible belt to avoid affecting the antagonist muscle. "

That is some serious engineering which you are going to find it difficult to replicate. Presumably they used dynamic (not regenerative :grin:) braking as well.

I wish they had used some type of breaking. To the best of my knowledge, they just turned off the power feed and let the motor "coast". They did not appear to be overly concerned at to what was happening at the 'off' state.

In the experiment, the frequency of periodic vibration stimulation is switched between 80 Hz (OFF-state) and 160 Hz (ON-state). Although 0 Hz is desirable in the OFF state, to achieve fast frequency switching between the ON state and the OFF state, the frequency of 80 Hz. which induces only a very weak TVR (tonic vibration reflex), is employed in the experiment because of the limited performance of the designed vibrator.

Frankly I am sticking with #14.

Yes, I also like the idea of a voice coil. Good size. Good response. Controllable output frequency and amplitude and not too expensive.