VDATP - a Volumetric Display using an Acoustically Trapped Particle

This project is a volumetric display that draws images in mid-air, in color.

By using phased arrays of ultrasonic transducers, it is possible to levitate a small 1mm foam ball and move it around at speeds greater than 1m/s. By moving the ball very quickly and leveraging the persistance of vision effect, this project can draw images in mid-air in a volume of 100x100x140mm. RGB LEDs are used to illuminate the foam ball at various points in its path to create multi-color images. 4 FPGAs are used to convert a position into the phased signals needed to drive the transducers. The FPGA can also rotate, translate and scale the images. You can even create animations - see a video for an animation of a butterfly flapping its wings. Kicad schematics and PCB layouts, FPGA code and simulator code are provided as well.

https://github.com/danfoisy/vdatp

Project Elements

board.zip (ZIP)

Board schematics and layout files

VDATP on GitHub (THUB)

https://www.youtube.com/watch?v=5JuckKflIqU

Discussion (3 comments)

weigu 3 years ago

The KiCAD design is amazing as is the huge amount of files in your FPGA folder. It would be great if you could provide more Infos on the calculations in the FPGA. Unfortunately I can't get the simulator running in Kubuntu 20,10 because of an opengl error (Unknown module(s) in QT: openglwidgets).
Thanks for this work and for sharing it!

Dan Foisy 3 years ago

Hi - yeah, opengl drivers are a bit of a pain in 'nix -I'm not able to advise on that as I did this dev work on a windows machine. The calculation on the FPGA is exactly the same as the one in the code that I showed in the video - it's just broken up into discrete operations and I've only used floating point where absolutely necessary. All the calcs are in the file CalcPhase.sv and each operation is annotated. Happy to answer any questions.

Agnivo Banerjee 1 year ago

Error code:(When I run the Holo.pro)

:-1: error: Unknown module(s) in QT: openglwidgets
:-1: error: [Makefile:243: Makefile] Error 3

screenshot-2023-07-17-222427.png (118kb)

weigu 3 years ago

Hi, thanks for the answer.
Did I understand correctly in the video that half bridges do not bring any improvement. A transistor would suffice?
Isn't the sound pressure lower with 10V than with 15V (the data sheet tells nothing) and do you have to protect your ears when the unit is running?

Dan Foisy 3 years ago

Actually, the drivers are full-bridge and so applying 30Vpp. However, the drivers get extremely hot at that voltage so I'm running them at 10V each (so 20Vpp applied to the transducers). There is a drop in performance by about 15% in maximum acceleration but I consider that acceptable. A half bridge would be suitable for this application - I don't believe a single ended driver would work very well given that the transducer can be modelled as a capacitor to a first order approximation.

I do protect my ears - obviously I can't hear 40kHz (and my dog and cats don't seem to mind) but some of the harmonics are in the audible range and are quite piercing. I suspect the ceramic caps are also resonating in the audible range.

weigu 3 years ago

weigu

1 Comment(s)

Roel Arits 4 years ago

Very fascinating and inspiring to watch.
It makes you wonder if a PID controlled motion and using a motion profile with minimum jerk using a limited acceleration and deceleration would even allow for higher speeds with "heavier" objects.
But it is already complex enough to just move it around.
This is a great demonstration of the power of FPGA's.

Dan Foisy 4 years ago

Thanks Roel!

I've been in touch with the orginal researchers and they have experienced similar distortions. They feel that the transducers don't respond linearly to phase changes and that calibrating the transducer phase response should help remove some of the distortions. I don't quite understand why phase response should act that way but it gives me an excuse to build a robot to calibrate each of the 200 transducers :)

Roel Arits 4 years ago

Yes, you are using transducers in a way that not many people do, so you discover new limitations.
Probably you will also have some temperature dependency on top of it all.
That is why these projects are great to learn and experiment, which opens the door to new applications.
Cool stuff.

1 Comment(s)

ElektorLabs 4 years ago

How do bats feel about it? ;-)

Dan Foisy 4 years ago

Not one has complained yet :) Actually, I was concerned for our dog and two cats but none of them react when I turn this on so it seems it's all good...