Do you know if it is better to call close a SD card file after each writing event or just leave it open until next writing? In term of power requirement?
In other word, will the idle current of a sdcard module will be lower when the SD file is close vs open?
I am also concern about the writing interval. If I write data every second maybe it is not a good idea to open and close the file every time? On the opposite, a open SD file will stay "open" for how long if I write nothing on it?
thank you
No idea.
What not measure the actual current with a multimeter, SD cards can vary considerably in how much current they use, so the current for one type might not be the same for another.
I haven't measured it, but my understanding is that the SD card's controller doesn't know whether the file is open or not. It has no concept of a "file". Only your SD library knows the status of a file. If there's no activity at the moment, the current drawn by the card module will be whatever it is in idle mode, regardless of the status of any file. At least that would be my prediction.
Consider adding external RAM like 23LC1024. Then you can buffer more and keep the SD card shut down. Microchip also makes a battery-backed version, if the idea of data sitting around in volatile memory bothers you.
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