Thougthfix described in his blog dated January 7, http://thoughtfix.blogspot.com/ a schema using Y-shaped USB data cable http://www.xpcgear.com/usbtype2atob.html. Could a USB travel charger provide the +5 V to both USB-keyboard and 770 USB connector via that cable?
The company hama has a power supply providing 5.4 V DC 200mA into a USB Type A socket . It "charges all MP3-USB sticks with permanently installed battery and is also suitable for other USB devices with power consumption up to 500 mA". It is multivoltage 100-240 V AC. I have seen it in a local department store at 16 euros.
Part number is hama 00014056, see techical details: http://www.hama.co.uk/portal/article...67/action*2563.