in the thread http://talk.maemo.org/showthread.php?p=489589
we've learned that it will be almost impossible to connect USB devices directly
to the N900 USB port.

An alternative idea came up: USB over IP,
which uses an external computer or special hub in which the devices
are plugged in. The hub forwards all USB IO to the N900.
This solution does already work for Linux and Windows desktops
http://usbip.sourceforge.net/

the relevant posts in the other thread are
http://talk.maemo.org/showpost.php?p...&postcount=573
http://talk.maemo.org/showpost.php?p...&postcount=575
http://talk.maemo.org/showpost.php?p...&postcount=578
http://talk.maemo.org/showpost.php?p...&postcount=579
http://talk.maemo.org/showpost.php?p...&postcount=583

the microcontroller idea was discussed independently in http://www.mail-archive.com/maemo-de.../msg20603.html
USB/IP was not mentioned