Sound travels approximately at 343 meters per second. When two speakers are placed opposite one another and they generate sound with same phases, then acoustic standing sound waves are formed.
These sound waves have enough power to keep small objects in the air.
The wave length is calculated by dividing the speed of sound by the sound frequency. Our speakers are 40Khz ultrasound transmitters and the sound wave length is 8.5 mm long.
Ultra-Sound-Levitation soldering kit contains everything needed to build such a standing sound wave generator.
On 14th October is the 20th issue of Open Fest – the biggest Open Source event in Bulgaria.
Olimex will have its traditional soldering workshop there from 10.00 to 18.00 o’clock.
Participation in both OpenFest and the soldering workshop is completely free of charge.
Everyone who wants to test his/her soldering skills is welcome. Olimex employees will help you with the soldering and guide you at the workshop.
For these who can’t participate in the workshop, the Ultra-Sound-Levitation soldering kit is available on Olimex web site for sale and can build one at home.
olimex 
Oct 12, 2022 @ 22:02:08
Very interesting, what’s the role of MAX232EN (U2) in this specific design?
It appears to be an RS-232 line driver/receiver, but the schema on GitHub shows we only use the UART in/out pins here (and not the RS232 ones) – probably used for isolation and/or amplification?
Oct 12, 2022 @ 22:12:37
Voltage levels multiplier from 0/5V to -12/+12V