Best posts made by basgoossen

I also had some issues with the M5Stack basic and SD cards. I was unable to read 9 out of 10 cards. In the end i ended up slowing down the SD card clock from 40Mhz to 10Mhz, this solved all the read issues for me. You can achieve this by editing the M5Stack.cpp file, in the function M5Stack begin SD is enabled using the following function:

// TF Card
if (SDEnable == true) {
    SD.begin(TFCARD_CS_PIN, SPI, 40000000);
}

I changed this to:

// TF Card
if (SDEnable == true) {
    SD.begin(TFCARD_CS_PIN, SPI, 10000000);
}

Since than i have had no more troubles reading from and writing to the SD card.

PPG is pretty finicky and the signal more often than not requires cleanup by software algorithms. Double readings are not uncommon and appear even in medical grade sensors. Most sensors used nowadays have multiple emittors or a single emittor with multiple sensors. The "evaluation sensor" with one led and one sensor used for this device will indeed require very precise and stable placement. Even so i'd recommend trying to get the raw signal out of the sensor if possible at 24-40hz (24 and 40hz are commonly used for PPG processing algorithms and usually a good place to start from). working with and visualising the raw signals will give you a much better insight of what you're measuring.

Current supplyed by the Core2 is not gona be a limiting factor in this. Noise of the voltage convertor could cause issues, but this can only be checked if the raw signal is analysed. Often sensors make use of motion sensors to discard readings during detected motion.