I've been for a while thinking about one project that would involve some sort of wearable device that has a component to it which simulates "pushing" at that spot, like a "finger" or "inverse button" pressing against the skin.
So far I have tried a small (5mm diameter) vibration motor buzzer, but the result was too "vague" of an impression, meaning it felt more like the whole area was stimulated, not one spot.
Another thing I have tried was using a very small solenoid (2cm x 0.5cm x 0.5cm), which kind of does best what I want to achieve, but here the problem is that the long part has to stand upright against the skin, when I'd like to get something more flat. I suppose because of the coil wire required for solenoids, there is no way around this fact, unless maybe converting the push force direction of the solenoid via some small mechanics maybe?
Does anybody have other suggestions of what could create such an impression of "a small push", or am I on the right track but it is more of a construction / mechanics problem? Would some sort of hydraulics construction be viable?
A TNS (transcutaneous nervous stimulater) feels very similar to needle pricking. And the sensation is very dependent on elctrode contact area and distance, a larger area givin a number feel and a smaller area giving a sharper feel. So perhaps two concentric electrodes can do the job
You might try one of those tiny 9g servos - there also might exist smaller servos to do what you want (look into micro RC planes for indoor flying) - but some of those may require custom fabrication.
If you don't mind fabbing things, though - you could build your own actuator in a number of ways, but probably the easiest would be to mod earbud or similar small speakers (heck, maybe an earbud driven with a good amplifier might be more localized on its own - perhaps try different waveforms as well?).
You could also try to build your own actuator, perhaps using a very small rare-earth magnet "button" over an etched "coil" on a PCB substrate; coat the coil trace with something to insulate it, then put a dot of silicone in the middle and let that set up. Then silicone the magnet on top of the dot; ideally what you are trying to do is "suspend" the magnet over the coil so that it can still move some when the coil is energized (so I don't know if my method will work - play with it). Then run your current through the "coil" on the PCB to make the magnet vibrate or move.
Another thing to maybe try would be small piezo discs driven with a suitable amplified signal, but such a device may not move enough to be felt - but it might be worth a shot anyhow.
There might exist the devices you are looking for (maybe google "haptic actuator" as well) - but they are likely to be very specialized and niche products that if they can be purchased in small quantities, will likely cost a bit of money.
nilton61, it might work, but I think for my purpose, where I would want several different, distinguishable, spots.
cr0sh, thanks for the many good ideas. I found something called "linear resonant actuator" (Vibration motors - Precision Microdrives), which, I believe, is in fact like what you describe in the DIY instructions - with the difference that the DIY could employ up or down states, when the vibration motor, even if linear, vibrates, thus giving a different sensation. Also the servos might be a good idea to try for my level. I believe both options would give me a good "pressed" option, but as far as coil winding and construction goes I am rather a beginner, so let's see.
About the DIY suggestion... will the etched coil be enough, in terms of coil loops - I was under the impression that the more loops you have the strong the inductive force?
Also, I found a couple of guides and videos online about coil winding, but they are more concerned with the actual physical winding. Anybody got a good tutorial link explaining the whole technical side of things, what to consider etc, what not to do?
cr0sh:
You could also try to build your own actuator, perhaps using a very small rare-earth magnet "button" over an etched "coil" on a PCB substrate; coat the coil trace with something to insulate it, then put a dot of silicone in the middle and let that set up. Then silicone the magnet on top of the dot; ideally what you are trying to do is "suspend" the magnet over the coil so that it can still move some when the coil is energized (so I don't know if my method will work - play with it). Then run your current through the "coil" on the PCB to make the magnet vibrate or move.
Hey cr0sh, another question about this after reading some online about magnets and DIY solenoids. Why would it be a magnet placed onto the coil wiring, and not just a piece of metal? Isn't the point of the coil to generate a magnetic field, to which the metal will than react? Or is your intention that the magnet would "move" even more due to the new magnetic field from the coil?
Anybody else feel free to elaborate as well, if it's within your electromagnetical engineering skills
