04-29-2021, 03:07 AM
(This post was last modified: 04-29-2021, 03:09 AM by danielt.
Edit Reason: Needed the Quick Edit box to properly link up the video...
)
What you see in the graph in wasp-os is pretty much what comes of the sensor. There is a little basic signal processing applied (DC removal, high frequency removal and automatic gain control) but what you see is basically the data the heart rate algorithm has to interpret to determine the heart rate.
The graph *should* show a strong periodic signal with the peaks occurring roughly half a beat *after* you feel your pulse in your neck (or if you prefer the troughs are aligned with the pulse in your neck). Occasionally there is a bit of noise so there are two peaks in close succession but algorithm will ignore these. You can see a live recording of the graph filling in this video which might offer some idea of what to expect. The samples in the video shows more noise than the screenshot about, especially in the first 10 seconds:
![[Image: 0.jpg]](https://img.youtube.com/vi/lIo2-djNR48/0.jpg)
One thing that is very important with optical wrist based sensors is not to apply any pressure at all when measuring. The sensor should work fine with a loose strap and even gives good readings when unstrapped and just resting on the wrist. This is because the sensor measures changes in blood diffusion near the surface of the skin and if you apply pressure to the sensor then you are basically squashing most of the "spare" blood away leaving nothing to measure!
A video might be useful and the captured data certainly would be! I'll look into adding support for that in the self test program when I get a chance (although it might be fiddly to get the data out since you'd need a GNU/Linux system with working bluetooth low energy to do that).
The graph *should* show a strong periodic signal with the peaks occurring roughly half a beat *after* you feel your pulse in your neck (or if you prefer the troughs are aligned with the pulse in your neck). Occasionally there is a bit of noise so there are two peaks in close succession but algorithm will ignore these. You can see a live recording of the graph filling in this video which might offer some idea of what to expect. The samples in the video shows more noise than the screenshot about, especially in the first 10 seconds:
One thing that is very important with optical wrist based sensors is not to apply any pressure at all when measuring. The sensor should work fine with a loose strap and even gives good readings when unstrapped and just resting on the wrist. This is because the sensor measures changes in blood diffusion near the surface of the skin and if you apply pressure to the sensor then you are basically squashing most of the "spare" blood away leaving nothing to measure!
A video might be useful and the captured data certainly would be! I'll look into adding support for that in the self test program when I get a chance (although it might be fiddly to get the data out since you'd need a GNU/Linux system with working bluetooth low energy to do that).