4duino cardiac coherence

This thing display the evolution of your heart rate along the time.
If you are stressed it's likely you'll get a curve with sharp edges like in second picture.
But from one second to the other, if you concentrate mind on your breathing or start meditation, or try to avoid thinking with words and pictures, it's likely the curve will become far softer, nearly sinusoïdal, like in first picture.
It's likely that you'll get a greater amplitude if you breathe deeply.
This is connected to cardiac coherence ( french "Cohérence cardiaque" https://www.coherenceinfo.com/ ), mindfulness meditation ( french "méditation de la pleine conscience"), and ... humm... in my humble opinion, to Holy Spirit (pneuma, breath in the Bible)

If you work with scad files, you'll need to download the pcb enclosure library - 3 ( thing https://www.thingiverse.com/thing:2808537 ) and the 4duino enclosure library ( https://www.thingiverse.com/thing:2808559 )

The main board is a 4duino: https://www.4duino.com/