This is a project I did about 6 months ago, when I was a lot less confident in electronics. However, I did get it working eventually. Thanks to mikeselectricstuff for inspiring the project with his video: Ultrasonic acoustic levitation
My initial design was somewhat complicated, involving an “auto-tuning” mechanism that allowed an Arduino to adjust the frequency of oscillation, generated by a 555 timer, using a digital potentiometer, to maximize the current consumed, as measured by a shunt resistor. Ultimately, I found that the ideal frequency was always exactly 25khz, despite the results seen by Mike (mentioned above), and so I just directly generated that frequency from the Arduino, and things worked fine. The driver just uses a transformer I wound on a ferrite toroid, with two primary windings wound in reverse directions, driven by two N-channel MOSFETs, each driven by a different pin on the Arduino. So ultimately I had a much simpler solution to build than Mike’s:
There should be resistors between the arduino pins and MOSFET gates.
And here is the transformer up close:
The transformer generated about +- 100v from about 7v input, from what I remember, and that was sufficient to levitate the bits of wax paper I was using. More power actually destabilized the levitation.
Here are some videos of the results:
This was true high-fps slow motion from my iPhone, before YouTube messed with it. Oh well.