[GraemeJ]

Ah... that rather depends on exactly which version of the OS you are running. It also depends on whether the tablet manufacturer has given you write pemission for the external card.

This whole external card thing can be a real PITA (as you will see from some of the threads here). I suggest you first tell us what tablet and OS you have. With a bit of luck, someone else here will have the same combination and will know how to get it working properly.

If you are running Android v5.*, then you will probably be OK, except that you will have to write to a dedicated directory - not necessarily the one you chose out of thin air.