Customize the PPG sampling rate?

[espruino-discuss2]

Posted at 2024-03-28 by user157845

I am conducting a research project using the Bangle2-watch. One of the aims of the project is to estimate the blood pressure from the PPG sensor. However, the research previously conducted on the subject shows that a sampling rate of >125Hz may be required to provide a resonable signal. In the documentation on the HRM its tated that the ppg sensor samples data up 50 Hz. I've searched the forum but without any luck in finding if it is possible to increase the sampling rate beyond 50 Hz. Looking at the documentation on the sensor it seems as if the sensor is capable of sampling up to 1KHz. But as already stated I fail to find any inforrrmatiopn regarding how to change the sampling rate. Any advice?

Cheers!

[gfwilliams]

Posted at 2024-04-02 by @gfwilliams

You can increase the HRM interval past the default (which I think is nearer 12Hz on Bangle.js 2) with Bangle.setOptions({hrmPollInterval:time_in_milliseconds}); (which you need to do before you turn the HRM on)

But the existing HRM algorithm won't work at that speed so you'll have to work yourself from the raw data - and you'll have to make sure you can handle the data coming in fast enough, as well as possibly configuring the HRM such that it can go fast enough.

There's an example of sampling at 200Hz in the Flash Counter app: https://banglejs.com/apps/?id=flashcount

Code that does it at:

https://github.com/espruino/BangleApps/blob/d6d03e1aac0a9de5a183cf74527e0ee04d530bc1/apps/flashcount/app.js#L4