Writing to an SD card uses the SPI bus, and on the UNO, digital pins 11, 12 and 13 are used by the SPI bus. Do not use these pins for other purposes when using SPI.
Writing to an SD card uses the SPI bus, and on the UNO, digital pins 11, 12 and 13 are used by the SPI bus. Do not use these pins for other purposes when using SPI.