Hopefully this may be of some help, I have also been trying to make one of these for the last few weeks.
So far, from purchasing this MHL - hdmi adapter
, I have managed to map most of the pins, but am having difficulties getting USB OTG to work.
Charge, HDMI, and PC data connection work, but i still need to find the USB OTG pins for "smart dock" mode.
I assumed that this would work for USB OTG
but it doesn't seem to work for me, it acts as USB Slave not Host (I.e. Connection to PC not HDD/Keyboard)
so far the pins i have identified:
(normal usb part)
Pin 1 - Vcc
Pin 2 - USB - (Slave)
Pin 3 - USB + (Slave)
Pin 4 - Sense (40.2K Ohm)
Pin 5 - Gnd
(extended USB Part)
Pin 6 - ? (Audio/USB host?)
Pin 7 - ? (Audio/USB host?)
Pin 8 - DP (MHL +)
Pin 9 - DN (MHL -)
Pin 10 - MHL ID (connected to ID Pin of MHL Adapter)
Pin 11 - Gnd
I will try and upload some images tomorrow, and a diagram of the plug.