New answers tagged sd-card
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It can't be done with an Arduino, but it can be done with other microcontrollers. You need a microcontroller with a direct USB ("native") connection plus a USB stack that is capable of acting as a USB Mass Storage Device. Something like the Teensy or chipKIT series of boards can do that.
Then you can write software that will, on command, detach the SD ...
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In general that's possible. But you can't read the sd card through the arduino's usb port. Instead you have to read the sd card via another protocol, e.g. SPI (look for the apropriate library) and send it to the pc via serial. You'll need software on the pc side to write the content that was read from the arduino to a file.
Take a look at the SD card ...
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It would be very useful, but afaik this is not possible, since the Arduino sketch you write communicates to the PC via the serial interface only.
The IDE/Arduino driver can use the USB to write your sketch and use the USB for communicating, but for sketches the USB (as direct medium) is not possible.
The SD card will not show up as a specific drive/map/...
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In Arduino SD library FILE_WRITE constant instructs the function to open the file for append, but in the esp32 SD library it opens the file for rewrite. Use FILE_APPEND to open the file for append.
File file = SD.open(path, FILE_APPEND);
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Unfortunately the DFPlayer cant write that data to the SD card. The Arduino has some non volatile memory of its own built in though. Theres 1K of EEPROM for the UNO. Notes on how to use it here: https://www.arduino.cc/en/Reference/EEPROM
If you can get what you need to done in 1K and its not important to your project that you be able to unplug the SD card ...
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The following answer assumes the Arduino is the master.
You can use any pin for that (at least any GPIO pin).
Multiple SPI devices can be connected to a SPI peripheral on an Arduino (in principle).
Every SPI device should have their own CS/CC pin, and is mandatory when you use multiple SPI devices.
For this reason, there is no single pin the SPI can ...
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You should not manually control the SD card's CS pin. By doing so you are confusing both the library and the SD card.
There is a special operation with SD cards in "SPI" mode that isn't part of the SPI standard as part of the initialization routine whereby the master (the Arduino) must send at least 72 clock pulses to the card with the CS pin held HIGH.
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