Asus Vivotab Note 8 - Charging and USB OTG at the same time

Hey guys, as stated in the other thread, I found a potential solution to charging and using data at the same time.

While experimenting with the charging hardware, I built a custom USB Y Cable, basically a USB extension with a power cable spliced in. The male side I then attached to a standard otg adapter (USB A to micro-B). This did not let the AVN8 charge, though data connection worked, and the host port did charge (i.e. an external HDD would spool up from the adapter's power).

Then I tried the Dell Venue 8 Pro's fix, of shorting the D+ and D- leads together. This doesn't change anything, it doesn't charge. Besides, this doesn't conform to USB standards.

I googled and read up on the USB Charging specification 1.2 (a dry 74 page pdf :S ), and found that there is an additional 5th, ID/Sense pin on micro USB. This can be either shorted to GND, or connected at 124k, 68k, or 36.5k Ohms for different features. Basically 124k is what we want, that signals the device to take power but also connect data.

So I put it all on a breadboard with a wired up micro-B plug, and the side of my USB Y-splitter where the male Data end used to be (where the otg adapter would previously connect).

Initiating contact with the 5th pin either floating (disconnected from everything else), having 124k/68k/36.5k to GND, or even on 100k to GND (makes it easier with 1 resistor), all gives the same result: it charges, but doesn't do data.
Initiating with 5th shorted to GND, it does data but doesn't charge (just like with the otg adapter).

Here's my preliminary solution: Initiate with the 100k from Sense to Ground to start charging, then flip a switch (or connect a jumper) between Sense and Ground to allow data to pass. This allows charging and simultaneous data transfer (only tested with USB stick for now).
Apparently, the charging circuit only tests the Sense pin once (at initiation), while the data circuits poll it constantly.



This all happened yesterday, and in testing some more, I saw that on the desktop taskbar the battery charge animation stops, even though it still shows the plug by the battery (it might do that anyway though, I'm not 100% sure). If you tap the icon it stops charging, the screen changes brightness to the "on battery" preset, and the icon switches to battery only (no plug). Seems like when you tap the icon the charge circuitry gets polled again, and that checks the Sense pin and sees it's in the wrong state.

So though this is more than we had up to now, it's not great...

I assume we would have to modify the USB driver to not poll the Sense pin, and just allow everything on USB since it is technically capable, but neutered by software. Would be a much easier task on Linux than Windows...

TL;DR
Simultaneous charging and OTG seem to work with special circuitry until you tap the battery icon, then charging disconnects.

 

Thanks for the help

You may know, but if you are not aware, there is a lengthy (46 pages) ongoing discussion in the Dell forum concerning this with the Venue Pro, which has the same hardware (or approximately )

Perhaps you should move this there, as they have been doing this for a while. They have solutions, but require either a Hub mod, or a couple OTG/Y cables.

The fact that there is not some kind of adapter for this is perhaps amusing, as there is money to be made, me thinks

 

Yup...uh-huh...sure. I understand some of these words!

All kidding aside it sounds like unless you're going to be starting a Kickstarter project and market this setup that simultaneous charging/data is not going to be very likely for most AVN8 users.

Disappointing how the Miix 2 does this right out of the box with a simple $5 OTG cable but neither the Dell nor the Asus can without a soldering iron and an electrical engineering degree.

 

Here I go again getting on the soapbox - HOW DIFFICULT CAN IT BE TO USE SEPARATE POWER AND USB PORTS? Good grief, it can't cost all that much. And if that's not possible (especially if you want to stay with the micro USB standard connection for power - truly a good thing) then just do the Miix 2 routine of a powering OTG cable...

 

Seems like a problem with Intel's reference design, but I'm still of the opinion it was intentional on their part. If they're doing all the design work for manufacturers to get these 8" BayTrail tablets for ~$300, Intel almost definitely doesn't want to see people using them as their main PC (and then cannibalizing more profitable products). Leaving off a dedicated USB and video out is a good way to prevent that. And from the looks of the Thinkpad 8 or whatever it's called, going with your own design seems to be much more expensive.

 

Exactly - 8" Bay Trails for Intel (actually any Bay Trail Device) are positioned as a companion device not a primary. In their reference design documents uses WiDi (Miracast) is their preferred method of video out.

 

All our tech devices suffer the same shortcomings. We hardly ever see any manufacturer get everything right. The Dell the best grippy rubber back of all of these. The Miix can charge and get data with a $5 adapter, the Toshiba has HDMI out, the Asus has Wacom, the Thinkpad 8 has a faster processor, more storage and a 1080 display.

Give me the Dell exterior/build, the Miix data/charge port, HDMI out, 1080 resolution, and a Wacom pen. Clearly all of these can be done, some probably relatively inexpensively, but nobody ever seems to get them all right.

Oh well. Gives us something to look forward to while while struggle along with the current crop of amazing little PC's.

 

NO NO NO NO NO - I don't want to elevate it to a quasi-desktop status. I just want to charge and attach a USB peripheral at the same time. WiDi always sucked to me, but I'll live with that for presentations.

 

You forgot that the Thinkpad 8 can be docked. Any digitizer would have made it very desireable for me...

 

As much as I like this little Asus, it is beginning to look like ThinkPad Tablet 3 or bust! That may be a plan - hold the 32GB Asus until Lenovo deigns to grace us with the TPT3 - what's the over/under on August 1?