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Author Topic: Conserve battery power on a project with SD card  (Read 434 times)
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I was confronted with a project that needs to run weeks with 4 AA batteries. It needs to use an SD card, LCD, possibly RTC, and two serial port sonic rangers.
I did a rough calculation with AA battery having 2500mAh of charge and two weeks of time:

i=2500mAh/360h=6.9mA so 7mA might be the max average discharge current. The data collection occurs every 15 minutes and takes a few seconds only. I guess the only way to make this work is to sleep in between.

I was wondering, how to turn off an SD card. Say I have a file open on the card. I save data on it. Then I flush the file to do the actual save. Then do I just use a MOSFET to cut the power supply? When I reconnect power to the SD card, just reinit it and open file again? I've not done this before and I may have to cut some shield legs to do it. Just wondering if someone has done this before. I'm sure the sonic ranger can be turned off with MOSFET but will need to test them. Any MOSFET to recommend in general? Do you see any problems with this simple scheme?

Thank you!
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During read and write operations the SD card will draw a couple hundred milliamps.  When it is idle it draws a couple of hundred microamps.

Given the other hardware, is  200 or even 300 uA that critical?
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During read and write operations the SD card will draw a couple hundred milliamps.  When it is idle it draws a couple of hundred microamps.

Given the other hardware, is  200 or even 300 uA that critical?

James, no it's not critical to draw 200-300 uA. I guess the next thing to do is to see if the level shifter and voltage regulator on adafruit sd logger will waste power too. Thanks for the numbers.
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