Here is a schematic:
When two of the flat-cable cables make contact, then a key is reproduced.
Of course not all of them produce a key, I did the mapping by examing the
membrane of the original keyboard. It's rather simple.
The keys in my device are connected as follows (look at the pictures and
read the README):
Note: Your keyboard may not look like this. I have no
idea what brand of keyboard to use, just try opening some and see for yourself.
(r) (u) (z) ([)(v)(x)(]) (b)