Hi,
How did you go with this? I am trying to do the exact same thing but with little success. Ive got similar readings for the sleeping SD (about 150uA) however seeing how the Ultra Mini Arduino I have uses 1.7uA while sleeping and the accelerometer I'm using to generate the interrupt uses 50uA it seems like a real waste.
Ive been using a transistor to switch the SD card on and off however simply interrupting the VCC or GND doesn't change the SD's power consumption that much. It only drops 20uA or so. More accurately, if I measure the power consumed by the Arduino and the SD its starts around 150uA, disconnecting SD vCC drops to 130uA, disconnecting SD GND drops again slightly. Then disconnecting Data In and the clock drops the power to 1.7uA (just the power being used by the board).
Disconnecting the Data Out is a bit unpredictable. If the SD is the only device on the bus the power spikes and quickly drops however if the accelerometer is connected by SPI the power spikes then slowly drops but never gets as low. I find this strange as while sleeping the accelerometer doesn't use the SPI bus, it simply delivers and interrupt and before sleep I'm calling SPI.end() to shutdown the BUS.
Ejecting the card does the same thing. Power spike then a decrease to 1.7uA
How do I achieve this with hardware. Put a transistor on each pin of the SD????
Any help would be great.