Thank you for your help
MarkT:
In theory I2C will work so long as the pull-ups are to 3.3V (3.3V will read as high to a 5V Arduino),
but you must check the I2C driver isn't actively pulling up on the bus.Without a common ground between IMU and Arduino it won't work at all...
And surely the base resistor goes on the base of the transistor after the diode(s), not in
parallel - you need to limit current however the transistor is operated.
check the attachment
MarkT:
I think you've fallen into the trap of using a single transistor to make a latching on-switch,
which can never work as transistors are inverting, so the powered down Arduino
is automatically going to be powering the transistor on via its protection diodes.
Can you suggest me any alternative that will work? I came up with all these because I've read that you cannot go sleep with arduino and a SD card module (bug of library that cannot re-initialize the card). The other thing is an EEPROM but the problem is its limited size.
