USBOTG and Charge Simultaneously on Stream 8

Question

To keep this thread as efficient and productive as possible for all those who it will be useful to: Unless you have in front of you1. A schematic of the Stream 8 USB port (USB port and battery power circuit etc)2. Source code of the BIOS firmware and kernel which control the hardware Please DO NOT reply simpy to say "this is not possible".  Given the above being true, you do not have enough info to say "not possible". If no one replys with a solution, let it be called impossible by default. Also please do not reply to say "I don't know how"  or "but I know how to do this other thing" thats also not so helpful. A BIOS update or other software update may be required by HP, Microsoft or both to make this really intuitive, and completely possible, functionality available. And hopefully this thread can be a consolidated effort by all of us who have the Stream 8 to bring any such necessary changes about.  A majority of other tablet PC are capable of this.  It seems that only the Stream 8 and a few others have trouble with it. ~~~~ I desire the ability to use a simple, perhaps standard, inexpensive cable (with minimal active electronics inside) that allows me to host and use one or more USB devices on the Stream 8 via its USB micro B port while this cable can also be connected to a standard charger and charge the Stream 8 simultaneously.  This means the cable has a minimum of three connectors.  One possible configuration is as follows (leaving the normal charge cable aside): 1. USB Micro B Male - to connect to the Stream 82. USB A Male - to connect to the AC charger (ie the one that came with the Stream 8)3. USB A Female - one or more connectors to plug in USB data stick, keyboard, mouse or even a hub. Connector # 2. above will provide power to charge the Stream 8 via conn. #1 and also supply power to the external USB device(s) via conn. #3 while they are in use - all simultaneously. A plus if the same cable can act as a normal OTG without a charger for when no external power is available.  Maybe this will require a switch or some active electrontics inside. The final part of this goal is kind of important for various reasons.  I would like HP, the maker of the Stream 8, to state in writing the correct mode necessary to do this so that other manufacturers or even do-it yourselfers can make maximal use of their HP tablet equipment. ~~~~ The neat thing this will alow a person to do with their tablet, is to work at home using the tablet like a desktop PC by connecting a keyboard, mouse, perhaps external display (with USB to display adapter) and work for a long time without being time limited by battery life because the charger supplies the power to everything involved. If there is only one #3 connector on the cable then an additional hub of coarse would be required to provide support for those multiple USB devices at once.  However it would be better if there were multiple of the #3 connectors built in to the cable itself.  This would be best because a proper USB hub also requires its own power.  Only one power adapter would be needed if the whole thing were integrated into one. ~~~~ I would really like replys from anyone who has already accomplished USB OTG plus simultaneous charging with the Stream 8. (independant of any published "correct" way is also welcome) The date today is 2015-01-16.  If by 2015-02-16 (one month) no one has posted a solution then lets start to bug HP and Microsoft about it shall we? ~~~~ Technical Background: I understand the possibility that the tablet software and or firmware needs to make a decision about which way power is flowing on the power pins of the USB mirco B port. I know that with proper design the electronic circuit carring these power signals inside the tablet could be sensitive to what is plugged in and safely decide for itself what to do without any need for software control.  For example by periodically testing/sensing voltage differentials or current direction to see which sides of the connector can supply power. But that is only one of many "could bes" Furthermore this may be non-standard with respect to the USB standard.  What appears to actually be the case with many OTG+Charge cables is that physical cues built into the cable or charger are used to signal to the tablet what the situation is.  Then the tablet's firmware/software recieves the signal, interprets what the situation is intelligently and responds by flipping the correct hardware control bits to turn on, or off power flow at the port and also control its direction in or out. I am not familiar with the USB standard.  Perhaps I could do more research, if I had faith that HP followed it with the Stream 8 or even that the standard covered this situation explicitly. But to a degree it seems like I am having to invent something that should intuitively just exist as it does with other tablets. No?  Maybe I am overthinking but I can't find any USB OTG + Charge cables that specify compatibility with the HP Stream 8. Anyway, I have been made familiar with two methods other tablets use to send the above mentioned signal to the hardware/firmware/software of the tablet to clue it in that it is time to charge vs. time to OTG or both. The first method is a 0 Ohm to 200 Ohm short between USB A pins 2 and 3.  Those are the bidirectional, differential data lines D- and D+ respectively.  In data mode all data goes back and forth on these lines.  When you charge via a data cable, it is the charger module which places this short, not the cable.  I have measured the short on three different chargers.  It is 0 Ohms on two of them, one of those being the charger which came with the HP Stream 8.  The other 0 ohms was generic.  The third was for an apple iPad and it measured about 53KOhms.  That is probably not the 0-200 Ohm resistor but probably it is the termination impedance indicating that there is some communication intelligent serial port in the charger itself.  Let it up to Apple to be different. This method is somewhat moot because this mode of signaling would prevent OTG + Charge because it seems unlikely that you'll be able to OTG when the data lines are shorted to one another and loaded down with such low impedance.  I could be wrong about this. . .  The other method I have seen suggested to work with some tablets and phones other than the Stream 8, is to short the USB Micro B pin 5 to pin 4 with 0 Ohms to 100,000 Ohms. USB B has 5 pins.  USB A only has 4.  The extra pin on B displaces the GND pin from pin 4 to pin 5 and makes pin 4 an ID pin. So this signal applies a pull-down to the ID pin (pin 4) or in some cases I have seen it suggested to short it down with 0 Ohms. Dead shorting things always makes me nervous.  If ID is a simple high impedance normally high input, a resistor could be used to make the voltage well below the low or zero threshold while also preventing the risk of damage when fooling with a device you don't have the schematic for. Still, 100K is a little high for a "pull down" in most situations I am used to.  Even a 10K would be iffy. A 1 K or 2 K seems pretty safe but then things are lower and lower current these days. . .   Anything but a dead short though if possible. So it seems possible to me that the device might be able to "identify" by the specific value of the resistor that is here.  In other words the resistor is not a pull down but actually an analog ID signature, in which case the exact value will be critical. So if this is the case, a guess isn't going to work. Obviously in any such scheme as described above, some chip inside the Stream 8 would need to be responsible for supporting such intelligence. I am hoping that the Stream 8 has such a chip. Likely a register inside that chip would reflect at all times what the state of the ID pin is with a binary number.  All that is needed is for the BIOS to address the chip and the register in it and read that number via the bus to determine what is going on at the port. Finally it would use that info to send hardware control signals to the power electrontics to set the proper direction for power to flow etc.  (and change the state of the icon on the screen of coarse) I am not sure if the ID pin method described is a USB standard or not either. There may possibly be a third way. But I do not suspect it would be possible with a non-active external device. In any case too complicated for the novice DIY for sure. The apparatus would need to act is some kind of bus extender.  Like an active hub.  But it would use the serial USB data lines handshake and in addition to replicating one or more additional USB ports, intelligently inform the tablet to get with the program which is "now we are going to otg and charge at the same time." This requires an intelligent external device with a CPU in it probably. It seems to me that many other tablets have managed accomplish the goal here witho the necessity for an intelligent external device and so the Stream should also be able to do so. There is a device which claims to be able to work with the HP Stream 7 and 8 and even provides ethernet and DVI ports in addition to the USB and of coarse charges the stream as well.  But its expensive because it is active.  Se here: http://amzn.com/B00OVDE0GC It is called a "Docking Station" A reference for a product that does exactly what I want (possibly without active electronics) is here: http://amzn.com/B00LTHBCNM It is by Kirin and it is a squid type device with four USB ports.  It does precisely what my objective is.  But reading in the reviews a Stream 7 user indicated that it would not OTG and charge, not exactly clear if it worked as an OTG USB hub or not.  Another reviewer indicated that it would not even support a single USB device much less charge on the Stream 8.  This device has a switch on it. I forgot to mention that some "hackers" have claimed to succeed with other tablets to trick their devices by using a multi step process to plug things in.  Usually in general they would get the tablet connected and charging first, then they would flip a switch or something removing whatever resistor or signal was presented by the first switch position. For whatever reason the tablet would continue to charge. Then the data lines would be free and they would plug in a usb stick and it would mount up correctly even as the tablet was still charging. Its like the power circuit has a latch that will not allow it to flip to "power flow out" mode so long as it senses power is still flowing inward regardless of what software is telling it.  Complete guess here. Such tricks  seem iffy to me.  Changes in the BIOS could change the way this works.  Also you can't be sure what is really happening if you don't have a schematic.  You could damage your tablet.  A lot of people go by the charging icon indicated in the OS to know if the tablet is charging.  But I am a low risk kind of guy and my policy is generally to not intereperet indicators to have any meaning at all the once a device is operating in a non standard setting.  Especially when its something i didn't build and couldn't fix if I fry it. Hypothetical reasoning: tell me what sensory data actually drives the state of the on screen charging indicator?  Does it reflect the hardware control bit that actually programs the power direction and state on the port?  Or does it measure the direction of power flow, say in the battery supervisory section of the circuitry?  Point is - none of us have a schematic because it is proprietary. To really be safe depending on how smart the hardware electronics are, the port needs to be in a deliberate "power flow in" mode. If it is in a "power flow out" mode and power is being delivered externally as well you wind up with the two power supplies driving the same power nets.  In that circumstance, the two opposing regulators which are both attempting to drive 5 V may have slightly different voltage calibrations.  That could cause them to fight each other with over 100% of their current capacitiy.  For example if one attempts to regulate 4.95 V actual and the other and the other attempts to regulate 5.05 V.  Current will then flow to the tune of 100 mV / a couple milliohms in the wires connecting the two.  This could be several amps. (a lot)  In other words, like I said:  You want the tablet to know that power is coming in not going out and to automatically hit the necessary internal switches to make this happen. Probably the tray icon should accurately indicate this but in some goofy situation it might not. There may be a chance the icon could indicate charging and still be burning up or stressing some circuit of the tablet or charger. Another possible thing I could see happening is if you play with those resistor signalled types enough you might find a resistance value that winds up placing the device in an intermittant state.  In other words it keeps flipping back and forth rapidly between OTG and charge.  It may give the illusion that it works.  You may have marginal communication with your USB devices and the battery might even charge.  But still lots of stress will be on the power circuit. It is hard for me to risk a perfectly good tablet if I am not sure exactly what I am doing. If some brave individual performs their own experimentation and verifies that it charges and OTGs and you tell the rest of us, then you'll be a hero. Maybe one of you has good knowledge about the USB standard to be more confident in such an experiment . . . like how is the ID pin 4 REALLY supposed to work for example? That is what I know so far.  If you think you can help further, thanks in advance, or if this has helped you, then your quite welcome.

Answer 1

To everybody who replied, thanks very much for your input. Firstly, beegmouse those two links are a great find.  Lots of good info. Dell™ Micro USB Dongle for Data and ChargingHow To Turn A $99 Tablet Into A Workstation! A few things still worry me. 1. The article is entirely about the Stream 7 not the Stream 8 (minor). 2. In the comments below the article a few people indicate that it charges, but slowly or remains at a steady power state. One of the commenters also provides a link to another similar OTG and Charge Device. Universal usb OTG Charger HUB cable for Tablet PC thinkpad 8,X98, M80ta,WT-8,Miix2,ME-400C,V8P,T100TA,W4-820,V975I,more models One commentor, Martinot states:     "I know others who got this one to work with HP Stream:" Then Martinot reposts the same thing but with a slight correction:       "I know some who got this one to work with HP Stream 7 and other Windows tablets:" So is it only Stream 7? or other Streams too? The charging "slowly" part kinda scares me.  It seems to indicate somethings not right.I don't want to fry my charging circuit and wind up having to RMA it.  Of coarse it could just be these people's perception as well.  Like watching grass grow.  I charged mine and it is normally kindof slow. It takes the whole night to charge when it is shut down and using the supplied cable and charger. Finally from the DIY perspective - Where's the magic?  I notice that the Dell device specs say that the Micro B female port on it is dedicated for charging.  So you connect your supplied cable and charger to that and the USB device to the other port.  (in the absence of a dock or USB hub)  I suspect there's an open on the data lines in the female micro B port of the DELL thinger.  That way the 0 Ohm short on data +/- that is completed by the charger doesn't make it through the DELL thinger to the tablet.  But does the dell thinger replace it with something else?  Can't be anything very low impedence or the data to the USB device would be too loaded down to signal. Maybe it puts something on pin 4 the ID pin.  Really hard to say. Also difficult to get probes on that little Micro B male.  I need to get some push pins or something super tiny to probe those tiny pins. ~~~ Thanks for your post and thread reference leo_kendall.(Parallel Thread on This Forum: OTG, charging and extrenal batery pack works HP stream 7) leo_kendall says that it charges "slowly" using this method as well. Others in that thread report slow charging, but one said no charge at all . . . maybe did it wrong? Interesting that you need to disable the Microsoft ac adapter device driver. Also thank you to eriri-el, I actually saw that entire video even before I posted the first time. Remember that the video demonstrates this with a Toshiba something or other, not a Stream 8. One thing that is clear to me is that tablets all have unique behavior with respect to OTG plus charge. Still to address the idea, I think this may almost be electrically identical to  leo_kendall's method.  However it could be slightly different at the Micro B end because one begins life as an OTG cable.  The other is something different. I researched the Y cable at Startech.   3 ft USB Y Cable for External Hard Drive - Dual USB A to Micro B The purpose of the cable is to provide the ability to connect the USB Micro B end to a single power hungry client USB device - such as external hard drive.  The other two branches go to the PC in normal use. One provides the actual USB data connection with the standard 500 mA of power. The other (red one) provides an additional 500 mA of power from a second USB port.  The point is to provide double the power to an ext HDD.  There are no data wires in the red one. In the linked video, the cable is being completely repurposed.  Not that it's an invalid idea, you just have to be careful when trying to be smarter than the designers. Basically both methods place all three ends (Tablet, Charger, and USB Device) on the same common power bus.  That is, sharing the same +5V and Ground nets. How these two methods may differ has to do with that fishy ID pin (pin 4).  leo_kendall started with an OTG cable.  Whatever the OTG cable had on pin 4 before, I think it probably retained in his mod.  Be that a resistor to gnd pin 5, a short to ground pin 5 or whatever.  Its probably embedded in the molded plastic of the Mirco B connector which was not cut open or modified right?  Who knows what is on pin 4 until you get a DMM connected to some tiny push pins and measure pin 4 on that particular OTG cable.  Whatever is on there, It makes sense that it signals to the tablet "Hey, I'm an OTG cable, do OTG stuff."  In the tablet's sense of the world, I think "OTG stuff" doesn't  include charging.  Hence why leo_kendall had to disable the ac adapter device driver.  Intuitively, to me "OTG stuff" would mean put out power to the connected device not take in power.  But they say it works so . . . What this means is connect the Tablet's battery to a +5V voltage regulator with a 500 mA current limiter heading OUTwards on the port.  Voltage regulators and current limiters are usually one way things.  And trying to put power through them the wrong way should not work at all.  If it does its because additional circuitry was implemented to allow it. But can you count out the designer to have gone that extra mile? Unless there is no signal at all on pin 4 or whatever. . .  Maybe the power nets of the tablet are smart enough to sense the power level inside and outside and judge from that to determine if it needs to supply power out or drink power in. I mentioned in my first post that "could be" So the difference is .. .   eriri-el's Startech Y cable is made for a completely different purpose. It might have the same thing on pin 4 or something different.  I can't tell from here.  Its not an OTG cable I know that.  Does an OTG have some special thing on pin 4?  I just don't know.  But the guy in the video from eriri-el didn't mention needing to disable his ac adapter device driver. ~~~ So some of you have working OTG plus charge.  I am still not 100% convinced of the safety.  I know I'm a chicken.  But that's just me. Needing to disable microsoft drivers, not unusual. Using Y cables for things they are not intended for, I dig that too. Cutting open OTG cables and twisting wires together.  Sure!  May I suggest that anyone trying this uses either some heat shrink tubing or electrical tape to completely insulate each wire once its connected. Charging more slowly than normal bothers me. Then again maybe it just charges slow because its booted up and the USB stick uses power as well. ~~~   What progress have I made?  Well not much in the way of OTG plus charge.  This cable has positively worked for a USB mouse and USB keyboard on my Stream 8: Kirin Micro USB Host Cable Male to 2x Type a Dual USB Female OTG Adapter I know I said not to do that, but it's relevant. I used a DMM (Ohmeter Setting) with alligator clips and some safety pins with a piece of kleenex to insulate them from one another. I measured between the Micro B pin 4 and 5 (ID and GND) on the above Kirin (OTG) cable and got close to zero Ohms in both polaritys. (Red probe on pin 4 while black on 5 AND red probe on 5 while black on 4) I measured 26 MOhms between the D+ and D-  (3 and 2)on the Mirco B.  (Hi Impedance) The power pins were straight through to both USB A connectors. Because its a dual port, I know it has to be a port replicator (hub) so there are some active electronics between the data lines, and those chips being powered by the +5V bus that shared three ways. So the Micro B end looks just like this electrically: ID Pin Schematic In the Kirin there are of coarse two USB A ports, and the D + and - are not straight through but have a replicator device in the middle. The most relevant thing is pin 4 I think.  I have seen it suggested to use a resistor as the ID pin short.  This is the first real OTG cable I have had my hands on to put a probe on it and it uses a wire not a resistor. . .  go fig.  Wire cheaper than cheapest resistor ?    yes indeed. I could probably do with this cable what leo_kendall showed without cutting it open by simply connecting the necessary gender changer cable from the charger to one of the Kirin's USB As.  But if that cable puts through both D +/- lines  the D+ to D- short seen at the charger might (digitally) do strange things to that port on the replicator.  A homemade USB A male - male power only cable then.  Now I just have to tell myself its safe to try. Another thing I noticed about the Kirin's Micro B male is that the pins are recessed at three different levels so as to create contact in a sequence vs all at once.  Level 1 being the first to contact, then 2 and 3 last.1. +5V2. D+ D- GND3. ID One final link USB Micro B Pinout for Hosts The last sentence on the page above is my favorite part "Additionally, most devices can receive power in host mode, even though this is not part of the standard." Well I have had enough of this for today.  I will be sure to update if I get this working.  For now be safe with your tablets all. 
Thanks again for your ideas and input.