I have some ideas and problems to bring into this thread.
Maybe someone can shed some light on my thoughts.
I have a rooted Razr XT910 and a car dock.
Also, i have a (in fact, more, but that is not part of the problem) 4-port USB Power supply for car and mains (Ansmann 5211013).
I'd like to use this power supply at home and in my car to charge my phone and have the ability to play movies and music from external USB storage. (I know it does not with the car dock cable because in there data lines are used for the audio.)
The reason for this power supply is simple: my wife and also the kids have devices with USB charge, and our car only has one outlet. So this handy thing allows me to use my Razr as Nav, while wifes phone can recharge and kids have power to play all the way to wherever we drive.
(Side note: it has 2 sockets noted "for iphone", 1 for "Samsung, Philips, Creative", 1 for "Navigation". Razr originally showed "AC" in iphone sockets, "USB-charge" in Samsung socket and did not charge in "Nav" socket. Sockets have different resistors on data lines: iphone has divider, Samsung has pull downs, Nav has open data lines. I removed resistors on my experiments. I used a battery monitor app to see the charge info.)
Also, i am able to solder, i earn my money in a electronics factory building all kinds of stuff, so electrically spoken i know what i am doing.
But, i am new to Android and Razr.
Experiment 1: I have bought a no-name USB-OTG cable ("micro B male" to "A female") and noticed the razr won't do anything, nor does the stick.
Trying a externally powered HDD did nothing also.
Conclusion: Power missing.
Experiment 2: I then modified a hub (D-Link DHub7) to "backpower" the host on his USB-B-Female, and upon plugging the Razr with its OTG-Adapter into the upstream cable of the hub, the Razr shows it's charging, also the hub powers the downstream plugs (usually upon recognition of the host). Plugging my stick into the hub makes it blink and appear on my Razr.
Conclusion: Works, but has too much of plugs, cables and additional hardware.
Experiment 3: I soldered 2 of the 4 sockets of the Ansmann power supply in parallel. I then plugged the hub in one of these ports (power on, ports off) and connected my phone to the other via the standard cable (micro B male to A male, the supplied data/charge cable). Phone showed "AC charge", but did not recognize Hub/stick (all lights were off).
Conclusion: There is some magic in the OTG adapter, so it's needed.
Experiment 4: connected hub with stick to bridged power supply ports, soldered A-male-to-A-male USB cable, plugged it into the other power port and the other end to my OTG-Adapter, then into the phone. Razr charged and recognized hub and stick.
Conclusion: works, but needs "special" cable and also too much of it.
I want to get rid of the Hub, so i started
Experiment 5: Stick to bridged port. A-A-cable to other bridged port, other end to OTG adapter, adapter to Razr. Razr charged, no USB recognition.
Conclusion: Hub is needed.
I do not want to carry all those
- power supply (with mains and car cable)
- hub with host cable
- OTG adapter
- standard data cable (to charge with minimum plugging)
My goal is to have the power supply and a data cable ready, plug it in (into iphone sockets = AC charge) and simply charge.
Or use the other sockets, plug stick/hdd in the other bridged port and use it.
I can live with having a second data cable (with pin 4 set to GND = OTG-Mode). I can also solder this data cable myself, i have the plugs at hand.
I don't want that OTG adapter (only 10cm and god knows why it's angled), because it's too short and dangly, and it does nothing because i need the hub to initiate data transfer and have the ability to supply power to the phone and peripheral. Using the hub on an PC would "divide by zero" because it powers the PC back, leading to at least unwanted results, if not burning something.
I want a nice solution, throwing the supply under my chair, connect 2m cable from there to my phone so i can handle it easy, connecting the stick or HDD also to the supply (out of my feets/hands range and on the ground, so it won't fall off the sofa or kill the USB plug on my phone) and maybe 5m HDMI to my TV, but that's another story.
Anybody out there who knows how to make OTG work without the hub?
Functionality is ok, cables are no problem, but the phone recognizes the Stick only behind the hub, i don't want that.
Sorry for the post being a novel, but i wanted to give you all my info.
I am sure i missed something, so please ask if you need to know something.