A belt that listens to breathing
Building a wearable breath sensor from a stretch band and a tiny microcontroller — and testing which band width actually hears a breath.
To let the cloud listen, each participant needs a way to share their breath that is cheap, comfortable and robust. Research-grade respiration belts cost hundreds of euros each. We built our own.
The belt
Zéphir designed a vest-like wearable with a stretch sensor band around the torso. Its reading changes as the chest and belly expand. A small ESP32-C3 board reads the sensor and runs on a 3.7 V battery with a charging module and a push button, so participants aren’t tethered by cables.
The firmware went through a few simple stages: printing one analogue value over serial, reading two sensors at once, then sending the sensor stream over Wi-Fi. In TouchDesigner, a patch receives the sensor stream, smooths the signal, detects the onset of each in-breath and out-breath using a lagged trail and threshold window, and broadcasts OSC trigger messages (/breath/breath0) across the local network to the main control software.
Which band hears a breath?
We recorded raw readings while breathing with bands of different widths (two 5 cm bands, one 10 cm, one 20 cm) under 1 cm and 4 cm of pre-stretch. The results are on the installation page. The narrow bands barely registered a breath above the noise. The 20 cm band gave a clear, readable wave.
Next steps on our roadmap: fix the sensors into belts, get the battery-powered versions working, and test breathing while moving as well as seated.