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Some background info: basically, I want to log a row of data (about 100-200 bytes) every minute. Saw the
E.openFilemethod, but since I don't write continuously, just usingappendfelt safer & simpler.
Would be powered by a power bank, because I need 5 volts for the PMS7003, but wanted to test the coin cell backup.
First I modified the Pixl as described in "CR2032 battery backup" section and did some testing with the coin cell writing a row every 3 seconds. Was working fine for a couple of hours, but eventually the SD card didn't like the low voltage :)
Then wanted to do some power measurements, but that took a "bit" longer than expected... Without a scope, just run reads or writes continuously for 10 seconds, and wrote the current value. That 30mA is the "average" consumption of the Pixl.Js + SD card.But probably would need a scope or some more sophisticated method to really capture what's going on.
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AkosLukacs
Thanks for posting that up - it's really handy to know about the consumption with the SD card, as I'd really expected that might be higher.
Where did the 30mA figure come from? In your use case (writing a small log message) I'd imagine capacitors would smooth at least the 10mA enough that it's not hurting the coin cell too much.
If you're interested, you'll find that writing to a file opened with
E.openFileis way faster -fs.writeFileis having to open the file first, which requires a few sector reads I believe... However for logging you'll probably want to have the file closed in case there's a power failure and it corrupts the file.