blengon:
I think I will try with this two: http://tinyurl.com/lh5eeyq and http://tinyurl.com/l3ky8uf
So you have checked that the connections match? I have not looked into that so far - I have both Pro Minis and Nanos but have had some trouble with the Nanos so have avoided them for the present.
blengon:
I do not think, that the Mini USB host shield fits to the Pro Micro, but it is nothing what could not be solved with several short cables
Quite so.
blengon:
But with the keyboard encoder: why it is difficult to interface, what could be the problem here? To my mind, it is maybe easier to interface the keyboard encoder then to solve the USB problems by hand ... but I could be wrong
The problem is that keyboard encoders are multiplexed - they activate one set of lines one after another and read another set of lines to see which crosspoints come up. To interface with such an arrangement you would have to determine which multiplex was active at any instant and provide a matching signal to correspond to the "virtual" keypress. That turns out to be extremely difficult to do. And a PC keyboard is at least a 10 by 12 grid - 22 lines - which explains why the chip you originally cited has so many legs.