OTG Y Cable with Power to Samsung 8 Tab

[jllaudio]

I'm trying to find  OTG Cable with a Y connector that can be used to provide power to a tablet and a USB Connected DAC (Dragonfly Red).  I have tried one that provides power to the DAC but not the Tablet.  The connection I would like to have is OTG to tablet.  A Y connector (with a Regular USB and female Micro USB) on the other end with the DAC in the USB port and the regular Tablet power connector connected to the other Y connector (Female Micro USB) to provide power to both the DAC and Tablet (in this case a Samsung Galaxy 8 Tablet).

Thanks for any help

[ripblade]

I'm trying to find  OTG Cable with a Y connector that can be used to provide power to a tablet and a USB Connected DAC (Dragonfly Red).  I have tried one that provides power to the DAC but not the Tablet.  The connection I would like to have is OTG to tablet.  A Y connector (with a Regular USB and female Micro USB) on the other end with the DAC in the USB port and the regular Tablet power connector connected to the other Y connector (Female Micro USB) to provide power to both the DAC and Tablet (in this case a Samsung Galaxy 8 Tablet).

Thanks for any help

I'm interested in an answer to this as well, though I'd also like to know if some kind of handshake is done for the app to sense the presence of a DAC, or is the grounded Sense pin of the OTG cable all that's required?

[ZeeWolf]

I've studied the same topic for almost two years, so here we go ;).
It's not about the cable, it's about what part of USB OTG specification your tablet does support - namely USB Battery Charging 1.2, and it seems that your tablet doesn't support it. Before USB BC 1.2 OTG specification said that OTG host MUST provide VBUS at all times, period. From device's I've tested only phones Samsung J5 (2015) and LG G4 (H815) support OTG host while charging out of the box (and I've tested a few). Some OLDER Samsungs allowed charging while in OTG host mode with ID pin connected to ground with either 124 kΩ, 100 kΩ, 68 kΩ or 36,5 kΩ resistor - but we're talking about 2013's devices, so rather don't expect it to work.
So now you have two options - buy ACA-compatible charger (ACA stands for Accesory Charging Adapter - rather pricey, ant there is still a chance that your tablet doesn't support ACA), or get modified kernel for your device.

I'd also like to know if some kind of handshake is done for the app to sense the presence of a DAC, or is the grounded Sense pin of the OTG cable all that's required?

Grounded ID pin only informs OTG host that some OTG device is attached, of course there is data exchange (at very least device descriptors reading) to determine what kind of device it is.

[ripblade]

I've studied the same topic for almost two years, so here we go ;).
It's not about the cable, it's about what part of USB OTG specification your tablet does support - namely USB Battery Charging 1.2, and it seems that your tablet doesn't support it. Before USB BC 1.2 OTG specification said that OTG host MUST provide VBUS at all times, period. From device's I've tested only phones Samsung J5 (2015) and LG G4 (H815) support OTG host while charging out of the box (and I've tested a few). Some OLDER Samsungs allowed charging while in OTG host mode with ID pin connected to ground with either 124 kΩ, 100 kΩ, 68 kΩ or 36,5 kΩ resistor - but we're talking about 2013's devices, so rather don't expect it to work.
So now you have two options - buy ACA-compatible charger (ACA stands for Accesory Charging Adapter - rather pricey, ant there is still a chance that your tablet doesn't support ACA), or get modified kernel for your device.

I'd also like to know if some kind of handshake is done for the app to sense the presence of a DAC, or is the grounded Sense pin of the OTG cable all that's required?

Grounded ID pin only informs OTG host that some OTG device is attached, of course there is data exchange (at very least device descriptors reading) to determine what kind of device it is.

Thank you so much for your input, ZeeWolf.  This is a complex subject to me but every little bit helps.  I recently acquired an OTG-Y cable to power a Dragonfly with a remote battery, but I've learned already that in order for it and the USB Audio Player to work correctly, that the battery has to be connected last.  With nothing attached to the cable the phone ignores the cable, so at least I know that more than GND+ID is needed to trigger OTG mode.

On the web I found a schematic for an OTG host charging circuit that uses a switch to lift the GND on the ID pin.  Now I can see why this is necessary as in OTG mode the phone will not charge even without the DAC connected. 

Thanks again!

[ZeeWolf]

No prob.
If you're interested I suggest reading "Universal Serial Bus Specification revision 2.0", especially chapter 9 - "USB Device Framework".