This project uses an Adafruit Circuit Playground Classic board along with a Pulse Sensor Amped to measure changes in heart rate variability (HRV).  Because fewer changes in heart rate variability are associated with healthy, relaxed states, these measurements can be used as a way to reduce anxiety and increase meditative calm.

What is HRV?

We normally think about our pulse as being a relatively constant value measured in beats per minute, but in reality, the interval between beats (inter-beat interval or IBI) usually fluctuates quite a bit.  This variance between heart beat intervals is known as heart rate variability (HRV).

When breathing is slowed to a rate of ~12 cycles per minute (1 cycle = 1 inhale + 1 exhale), respiratory & cardiac rhythms tend to fall in sync with one another and HRV fluctuations become less erratic and more amplified resembling a sine wave.  This synchronization is considered indicative of a relaxed, healthy state of being where anxiety is reduced and clear, calm thinking is enhanced. 

So, if we measured and graphed the time between heartbeats of a stressed person, it might look something like this:

And the same type of measurement made on a zen master might look something like this:

The goal of this project is to create a device which will help someone achieve a smoother, sinusoidal HRV pattern like the one above.

You can read more about HRV, coherence, and related topics here:

Disclaimer: This is not a medical device and should not be used for any official diagnostic or otherwise life-dependent medical purposes!

What you'll need:

To build the relaxation trainer you'll only need the following:

This guide was first published on Sep 20, 2016. It was last updated on Sep 20, 2016.
This page (Overview) was last updated on Oct 07, 2020.