I saved SD power control to the end of my quest for low power logging, because of all the potential weirdness that could arise with the Arduino libraries. But after a reasonably thorough round of testing it all seems to be working OK with a BJT switching the ground line.
I realize that I might be playing with fire, but the potential gain in operating lifespan was simply too big for me to ignore. Unlike RTC pin powering, which I have a great deal of confidence in, I will consider this technique experimental till I see a whole crop of loggers saving data safely for more than a year...
Bump!
EKMallon I was wondering if you had any more development with powering down SD cards?
In my application I am monitoring an MEMS accelerometer and writing to an SD occasional. I expect this to happen about once per hour so using SD IDLE (200uA) is still too much for our application.
However, problem is the accelerometer also uses the SPI bus so I cannot fully disconnect the SD. Ideas?
The easy solution would probably be to find another accelerometer (I2C or analog) so that you can shut the SPI down without affecting the sensor. The other thing to look at would be adding a software SPI interface for the accelerometer.
That's what I did to keep the nokia 5110 screen off the hardware SPI bus, which is essentially the opposite situation (I'm shutting down the screen, but leaving the SD sleeping...)