Oliver Child's Raspberry Pi Pico-Powered Sonolithographic Machine Makes Pretty Patterns with Sound

Maker Oliver Child has penned a guide to performing sonolithography — the science of controlling spray patterns with sound — at home, using less than $125 in parts, including a Raspberry Pi Pico microcontroller board.

"Sonolithography is a way to pattern finely sprayed materials onto different surfaces using sound. The way it works is that tiny droplets go through an acoustic field and experience a very slight force towards the field lines," Child explains. "If we spray a mist of dyes and inks into these fields, they will pattern to produce interesting shapes that uncover the invisible acoustic forces. [It] may have applications in cell patterning in biology, patterning of conductive traces and active materials in fabrication, or other fields. It also is just really cool to explore the different aesthetic shapes you can make with it."

Traditionally, sonolithography takes place in a lab using expensive equipment — but, by following Child's guide, you can do it at home for under $125, "which is mostly the price of the transducers themselves," Child explains, referring to the 16 Murata MA40S4S 40kHz transducers used to make the sonolithographic array. Other parts used in the build include a pair of 74HC595 shift registers, eight TC4427 gate drivers, a few decoupling capacitors, a Raspberry Pi Pico to control everything, 3D printed parts to build the array and liquid reservoir, and — key to actually producing the spray — an atomizer module, usually sold to those trying to make their own humidifiers.

"We make use of the Raspberry Pi Pico's Programmable IO (PIO) to serialize the waveform data for each of the transducers," Child explains of the way the array works. "This works by having a separate piece of code that runs in parallel with the main processing on the Pico that's only role is to read the wave form data and set up the appropriate timing to send the signals to the shift registers."

"Controlling the phase shift and amplitude of each of the transducers can be done in various ways through the serial interface. I've built a controller I call the Orbogrpah - it's a set of slider and rotational potentiometers that control the relative phase and amplitude of each transducer. It's a lovely device and nice that the whole system is self-contained between the transducer array, driver circuit and controller.

"The idea," Child continues, "is that by having a physical controller you have some level of tangible feedback. In keeping with the theme of making a low-cost and accessible introduction to sonolithography, I've also built a web interface that you can use to control sonolithography arrays."

The full project guide is available on Instructables.