# USB OTG + Pass-Through Charging?



## FranzVz

Do they make any USB OTG with a side-charger?

What I mean by that is something like this:










This was a TV-Out cable I bought for my HTC Inredible, and it supported charging the device while also using the cable. Are there any USB OTG's that support charging _and_ mounting a drive?

The idea is that I'm going to build a custom dash mount for my Nexus 7 in my car (for music, gps, etc...) and I would like to know if I can charge it when it gets low in emergencies at the same time that I plug USB Thumb drives into it.


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## altimax98

From what I know there isnt a pass through for OTG. I believe once OTG is enabled the port switches from power to data.

I could be wrong though


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## Kpa2727

i found this awesome article that shows how otg works i'm going to be starting solder work very soon in my Sd card adapter add on i'm going to put inside the nexus 7.

take a read http://forum.xda-developers.com/showthread.php?t=1092493


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## Kpa2727

It dawned on me i didn't fully answer the question, So to make it clear, there should be no reason that you can't get a pass through. The reason why being. Usb charging should work as that once current flow increases it should sense this and enable charging. so a otg reader should use minamal voltage maybe 100 milliamps tops.So if you piggybacked onto this you could charge and read the devices at the same time. considering the device usually controls power demand I can't see this being a issue with power. In a nutshell a pass through or Y cable should be more then capable.


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## Snow02

Kpa2727 said:


> It dawned on me i didn't fully answer the question, So to make it clear, there should be no reason that you can't get a pass through. The reason why being. Usb charging should work as that once current flow increases it should sense this and enable charging. so a otg reader should use minamal voltage maybe 100 milliamps tops.So if you piggybacked onto this you could charge and read the devices at the same time. considering the device usually controls power demand I can't see this being a issue with power. In a nutshell a pass through or Y cable should be more then capable.


Charging doesn't work through an OTG cable. Just tried it. You'll need to break out the soldering iron and wire power directly into the device if you want to make this work, I believe.


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## Kpa2727

well how did you test it a male to male? cause were talking a port designated for charging , not forcing a otg cable to do it. something purposely built for it. I'm debating waiting on my otg cable or just soldering into mine for a internal add on.


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## Snow02

Kpa2727 said:


> well how did you test it a male to male? cause were talking a port designated for charging , not forcing a otg cable to do it. something purposely built for it. I'm debating waiting on my otg cable or just soldering into mine for a internal add on.


I'm retarded. Haha. It does work. However, it doesn't appear to mount the storage. Unplug the power source, and it mounts fine. Mount the storage first then apply power, and it doesn't charge. So you're still back at having to directly wire in power.

Tested using this cable:









It may be worth seeing if you can charge via pogo pins while using an OTG cable for storage (anyone with a pogo pin dock for the nexus and an OTG cable wanna chime in here?). I'm guessing you can, and this would actually be the best way to go if so. Just build them into the mount.


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## Kpa2727

In theroy this is great, i checked my mailbox and my OTG cable was there, i been messing with it the last few minutes, if i had to guess otg is drawing enough power to not reach the trigger threshold or it's a kernal issue, being that i'm not planning on ever having mine plugged in and using the sd otg it would be fine, so can you test this theory for me since i don't have y cable. plug in sd card but don't mount it, now plug in the charger, does it charge? now leave the usb plugged in still, unplug the charger, will it mount? i'm just making sure if this is what you said happens or not. cause if i solder in a usb drive like i plan to. I need to make sure mounting and unmounting will be my difference between charging, not physically un pluging the storage.


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## Kpa2727

if you test this for me i'll be glad to include you in credits of my full write up/build log/guide


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## Kpa2727

also my next hurdle, installing apps to the otg....yikes


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## Kpa2727

any update to my theory Snow?


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## Snow02

You are not going to be able to utilize external storage and charge through the usb port at the same time.


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## Kpa2727

No i get that but can i go etherway, charge , no mounting, no charge, with mounting. I got my new soldering iron on the way so at this point i'm taking nexus 7 under the knife in a few days ether way, i'm just trying to plan ahead.


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## Snow02

Kpa2727 said:


> No i get that but can i go etherway, charge , no mounting, no charge, with mounting. I got my new soldering iron on the way so at this point i'm taking nexus 7 under the knife in a few days ether way, i'm just trying to plan ahead.


Correct. It's one or the other. The only issue is you have to disconnect the sd card or the power to switch. Toggling stickmount isn't sufficient. So if the reader will be externally accessible (slot in the case to get to the sd card) there shouldn't be a problem. But if you're planning on it being internal, you may have an issue.


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## Kpa2727

Snow02 said:


> Correct. It's one or the other. The only issue is you have to disconnect the sd card or the power to switch. Toggling stickmount isn't sufficient. So if the reader will be externally accessible (slot in the case to get to the sd card) there shouldn't be a problem. But if you're planning on it being internal, you may have an issue.


 ouch, i was afraid you might say that, ok I may have a soloution for this but won't know till i test. Thanks for the input once again.


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## FranzVz

This is pretty interesting, I might buy a secondary N7 (or used) down the months and play with the hardware to see what kind of Frankenstein-ish things I can do with it


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## js3kgt

Kpa2727... I am wondering if this would be doable and have a pnp transistor and a diode to watch the voltage on the second female micro usb port and cut the ground from the sense wire to allow for the charge to take over and stop the OTG connection. That way you could wire directly inside the device and not have to disconnect or switch the wires. It has been a long time since my EE courses though so I might be wrong.


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## papatel

So I got tired of waiting for a kernel hack for USB OTG+charging.

For those of you who are integrating this onto a car or somewhere with permanent power, I have a solution for USB OTG + powering the nexus 7. Ironically this solution can make you some $$  Here are the steps:

1. Take off the back panel of the n7. It is Very easy to do and you will not damage anything unless you are an ape.
2. Take a look where the battery connects to the tablet. There are 6 wires. We care about the 2 red and the 2 black ones. Take note of the pins that the two red/black wires connect to on the n7 side.
3. Remove the battery.
4. Solder a wire to either pin of where the red wires connected, mark this +. Solder another wire to either pin where the black wires connected, make this -.
5. Find a place to run the two wires out while being able to close the case. I don't use the headphone out (I use a USB DAC) so I just ran them through there.
6. After putting the cover back on, Apply +5V (current capable up to 2A) to the two wires and boom, the tablet will boot up and run as solid as a rock.
7. Sell your N7 battery

USB OTG will work like a champ in this configuration. I have a usb keyboard and a 500GB hard drive connected through a hub. I like solution in a car since you no longer have to worry about battery temperature issues which can be an issue in a car... The only disadvantage so far is that the battery charging icon is red since it can't find the battery... doesn't bother me though. It's a constant reminder of my victory over USB OTG + charging at the same time


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## Snazzy

papatel, thank you so much for posting this. I'm mounting my Nexus 7 in my dash and was debating using an OTG solution. For your 500GB HD, is it powered by another source (i.e. powered hub) or straight through the OTG cable?

Thanks!


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## Sengir

Try this








http://rootzwiki.com/index.php?/topic/30615-Can-you-charge-&-USB-Host-mode-simultaneously?#entry957309


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## mbc0

Hi Guys,

I am a complete noob when it comes to roms & Kernals.... I have read EVERY page of this post along with many other threads on XDA Developers and more & am still unsure of the best way forward.... Can someone please help me in a spoonfed kind of way with what I need to do?

My sole purpose for this tablet is to have it installed in the car, I dock the tablet using a Brodit Car Mount and I have successfully rooted my Nexus 7 3G and installed Stickmount and am able to use my 1TB Samsung S3 Portable drive and have the audio connected through the headphone jack (not interested in DAC) but obviously suffering very fast battery drain (about 4 hours) All I want to do is have the same configuration but with the ability to charge from my 2A USB Charger in the car 

I really cannot understand what I need to do with the roms & kernals and what I need to do with making a cable (impossible to buy one of these "Y" Cables in the UK anywhere!

I know I must be a pain in the A** to you experienced guys but if one of you could find the time to help me understand, I will in turn pass this information onto my friends that are in the same boat

Many Thanks to everyone who has supplied so much information on this subject I just need the few pieces of the "understanding" puzzle put together for me...


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