The Adafruit Grand Central M4 Express has a built-in SD card connected to the SPI bus, so no wiring or soldering is needed!
To mount the SD card, use the following code. Remember to put it in the file mount_sd.py on CIRCUITPY so you can easily call it from code.py or the REPL with import mount_sd
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import board import busio import sdcardio import storage spi = busio.SPI(board.SD_SCK, MOSI=board.SD_MOSI, MISO=board.SD_MISO) cs = board.SD_CS sdcard = sdcardio.SDCard(spi, cs) vfs = storage.VfsFat(sdcard) storage.mount(vfs, "/sd")