I was thinking about the requirements for the other half interface, and my bet is that USB would indeed be the best candidate. USB gives the possibility of using the broadest spectrum of devices, it's well specified, and works like charm on Linux devices.
I see the need to have both USB client mode (for computer connection) and USB host mode (for gadget connection)

However, if it is required that the interface would both source current to devices, and be able to sink current (for a contactless charging other half, for example) I think more than just pins for one USB interface is preferred.

If you just have exposed VCC, GNC, D+ and D-, it's possible to use the VC pins to both source and sink, but this requires complex (and error-prone) logic to determine what mode the pins are operating. Same way having just D+ and D+ requires backend to configure the device to work either as USB host or USB guest.

Hence I propose, that there should be 2 separete USB interfaces:

• one interface for USB host mode that can source current, maybe up to 150mA (there's battery life to consider, we don't want to drain it too fast)
• one interface for USB client mode, that can sink current from a charging solution

Alltogether that makes 8 pins, or let's say 7 if the interfaces use common GND.

Solar would be ok, but what is so special about it? Nokia had this option (Nokia battery BBT-1L) 15 years ago for Nokia 1610 / 1630...

y'all are behind the curve. im already working on the fleshlight attachment

I'm looking at how RFID technology is now using sensors to transfer/stream data.
NFC, if i'm correct is essentially an evolution of RFID. It transmits data to trigger a configured set of events (in the case of Mobile, usually as a catalyst for and ID establisher for bluetooth/wireless comms)
Amazing potential to use current RFID - sensor input embedded in theother half to pick up heartrate, temp, humidity, or replace sensors with embedded data or information. include a usb connection to load that info and you have a fully replaceable data store and management solution that you could swap between handsets.
One back with all your work stuff on it and at the end of the day, swap it over for all your movies and music on the trip home.

Yes. Like I said in post #42 , it must support USB 3.

This opens up many possibilities and the vendors does not have to do a lot to come up with solutions. Vendor can design docking station OH with a USB hub and a bunch of ports to support what ever devices.

The interface must be clean and unique. I am not sure if they should go with standard USB interface. Apple always wins with a non-standard interface. I hate that but this is a special situation and the cover has to hold on to the body without making it too bulky. So there maybe a reason for a custom interface that makes it clean, unique and cool.

it should have -
a slide out keyboard
infrared
fmtx
pressure sensitive screen (for painting)
flashlight
then only we n900 users could replace new sailfish phone with our n900

Well, there's already a USB slave interface up top, so why add a third USB PHY?

I think that in addition to 5 pins on the side of the device (see here), a dumb V+ and V- a la Nokia barrel connector power supply would do.

Assuming the connector on the external housing is keyed with a small notch, I doubt people would stick the USB portion into the charging portion.

Various things come to mind...

DVB-T
fmrx/tx
Camera optics/microscope/macro
Dockingstation Pins (four tiny little gold dots)
Magnetic Car Holder
DiaryCover(TM)
Inductive Charger
Cardreader SIM/SD/magnetic
Laserpointer
DMXcontrol
192kHz/24bit Stereo-port
PDMS/Samsung'sMI
5GHz HIDserver (wireless mouse/kbd for your desktop)
Guitarhero-like buttons
Braille interface (Klaus Knopper's wife comes to mind)
Sensors humidity/temp/wind/light/distance
Scales
Money clip
CD/DVD/BD-Player

knock yourself out!

That's brilliant! Finally Dave999 can have his Disc-phone.

Well, I was thinking of an use case where you have more than one functionality in the same OH unit, like when there is both wireless charging device or spare battery and something that acts as an USB client.

My idea here was that the charging interface should propably be USB, as that is already implemented in the device and has the proper current sourcing negotiation.
If, at the same time you want to have something there that is controlled by the USB it would need to have the other USB port also.

BTW, about the picture in your post, where you cansee the pins on the backside, is that a real device or an illustration?
If that's a real picture then I belive you are correct, and the OH interface has just one USB.
However, this then begs the question how do you safely determine whether the VC pins are sink or source? And what about the use case where you need both at the same time?

(well, of course you can argue that the VC pins are ALWAYS sink and since the OH in question is able to source current it should be able to power itself... but what about when it's not connected to charger, or if it contains a spare battery, the battery's flat?)

PS: Now as I looked at the picture again I feel there could be another solution to this problem. As it's 5pin connector, ther could be the following pin assignments:

• GND
• D+
• D-
• Vcc_IN
• Vcc_OUT