Display text in the 20 kHz ultrasound spectrum
docker run --rm ghcr.io/montlhery/noirtier message > output.mp3
Use a 35 mm piezoelectric speaker, a microSD card and a DFPlayer Mini with IO_1 connected to GND to automatically play the generated MP3 file in an endless loop.
Power consumption is approximately 40 mA at 5 V.
- Desolder the microSD connector from the DFPlayer Mini and solder the microSD card directly to the circuit board.
- Enclose the DFPlayer Mini between two piezoelectric speakers with the silver parts pointing inwards.
- Solder all the connections, and terminate the power cables with a two pin female 0.1" header.
- Fill the perimeter using copious amounts of solder and desoldering braid as a filler.
- Use a file and sandpaper to remove excess solder and polish the burrs.
The result should be a flat disk with only two holes from the power header flush with the border.