Bad readings only at Red LED (MAX30101 with Xiao nRF52840)

[sacergoose199]

Good day!

I need the Red, IR, and Green readings. I have the MAX30101 and Xiao BLE nRf52840 with the models shown in the pictures below.

I just used the Hexiwear sample code for max30101 and only added lines in the proj.conf, xiao.overlay for dts, and main.c as follows:

The problem is that while the Green and IR readings are normal, the Red readings reach an upper limit of 262143 when a finger is placed:

These are the readings when the finger is not placed:

I tried uploading the same code on a different MAX30101 board (Heart Rate 4 Click by MikroE) which produced the same Red readings.

I tried using the heart rate mode only to only use the Red LED which also produced the same Red readings.

Where and what could have been the problem? 

Thank you in advance!

[hmolesworth]

Perhaps try reducing the drive current for the red LED; I don't recall having trouble with signal level, but didn't use this code:

Table 8. LED Current Control
LEDx_PA [7:0] TYPICAL LED CURRENT (mA)
0x00h          0.0
0x01h          0.2
0x02h          0.4
…              …
0x0Fh          3.0
… …
0x1Fh          6.2
…              …
0x3Fh         12.6
… …
0x7Fh         25.4
… …
0xFFh         51.0

[sacergoose199]

Thank you for the tip! I changed the current to 0x33 similar to the default IR LED current and it looks fine now!

[hmolesworth]