What method do you recommend to log analog values read to an SD card at high speed?

[Arakistech]

What method do you recommend to log analog values read to an SD card at high speed?

[stg]

I have no recommendation and it depend a lot on the rest of the application.

Generally, I suppose I would:

• Set up an interrupt handler on a timer to do ADC readings
• Buffer ADC readings directly in the interrupt handler
• Use a fast SD card library, probably using DMA
• Write buffered samples to SD card in the main loop
• Implement buffer overflow detection and a method of notifying the user
• Do a bunch of testing to find the limits

For really fast SD card access you usually need a proper "four-bit modes" SD card peripheral in your MCU and I haven't checked if the ESP32's can do that.

SD card speeds also vary, so it would be important to be able to detect and notify when things fail-

Plenty of testing to find suitable buffer sizes to deal with any latencies that may arise from accessing the SD card via the library would be recommended.

SD card libraries are complex and may or may not block, may or may not retry, may or may not... etcetera.