I've also made a cover for all of the electronics, but that part is optional.
STL-files and some additional info about that can be found at Thingiverse: http://www.thingiverse.com/thing:170995
What you'll need:
1 Mendel90 printer
1 "Type19 SD to MicroSD MemoryCard Extender" (Search it on Ebay, may also be listed as "SD to MicroSD Card Extension Cable" or similar)
2 pcs of double sided adhesive foam
Some regular adhesive tape.
Step 1: Mount the SD-card Extender
The best place I found is on the right side, sticking out sideways.
But if you're not going to make the cover, you can place it wherever you want. I found it best to mount it sticking out a little bit, to make it a bit easier to get to the SD-card. But place it the way you like.
If you'll use the electronics cover, place the new SD-slot 110mm above the power supply. Or if you've already printed the cover, mount the lower part of it and place the SD-slot just above it.
How you'll run the flat flex cable may depend a bit on how you've mounted your other wiring. But on my printer the best way was to go under all of the cables, and under the Meltzi PCB and come up just by the µSD-slot, and then have the rest of the flat flex to go zig-zag a vouple of times, and then I taped it together nicely.
Note: Don't bend the flat flex cable in sharp corners, you want it to round of nicely or it will most likely break.
If you won't be using the electronics cover, you are now done! Insert a standard SD-card into the new slot and it should all work great.
Step 2: Fix the Cover
It's easy, just make the measurements on the case like in the pictures and make marks. I used a knife to mark it, no problems.
It may be a good idea to measure on your own printer, since you may have mounted the SD-extender a bit wrong. But the distances shown in the pictures worked great for me.
And then cut off that corner piece.
I like cutting PLA using hot wire. Like 30mm of kanthal wire between two crocodile clips hooked up to a lab power supply works great.
I also used a "third hand" to hold it while cutting, just to make it a bit steadier.
Or if you print the latest version of the cover, with the hole for the SD-card, you should not need to make any modifications to it. Just mount it on the printer and you're good to go.
Good luck printing and keep on making things better!