Photoplethysmogram 2

The MAX30102 arrived and I spent some time. I’ve also gotten metal disks and will try to make rings with polymer clay to hold the electrodes for GSR on better. As such I’m busy and this will be brief.

The device itself is tiny.

After reading through the datasheets, I wrote something to set registers for SpO2 measurements (IR and red LEDs active, there’s a heart rate mode with only one), and after having bad luck with guessing appropriate settings, eventually found all the recommended settings in the application notes for the demonstration board.

I had a bit of difficulty getting data from it, if just because it’s smart. There’s a 32 sample FIFO circular buffer for the data, which is accessed by repeated reading a single byte register. The read and write pointers are accessible but unnessesary for this, as they both automatically increment. Samples are 2 24 bit numbers (IR and red channel). As is, the program I’m using to read data sets an interrupt enable flag on the MAX30102 to check it for available data and then checks it repeatedly. There is also an almost full interrupt, and I spent some time getting the MAX30102 to trigger the nucleo, but I’m still having trouble reading multiple samples from the ADC.

See, which I will hopefully have enough time to make nice because I plan to use this with hand tempurature and GSR for biofeedback.

Anyway, in the end I got a reasonable trace for reflectance values.

RED and IR reflectance values

Author: Garth Whelan


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