iPhone Charging Can't Get 2V Over USB Data +

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pittsburgh

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Joined
Nov 8, 2009
Messages
240
Location
Nashville, TN
I'm modding radios with apple AV cables, see link below, so that you can play your iphone/ipod through an old radio. I've done this by purchasing apple AV cables, cutting them apart, and hooking them up on the inside of the radio.

  I'm having a problem with charging/syncing. I cannot get 2V DC to flow over the data + pin of my USB connection. This is for use with charging an iphone. The 2V data + USB pin allows data to be transferred to and from the ipod allowing for charging and syncing when connected to my computer. The other voltages check out, 5V, 0V, and 2.7V over the data - connection.

  As a test I bypassed my computer's USB port and went straight to an apple outboard charger. This works every time. I've checked audible continuity between the final connection the end of the AV cable and the USB A connection that goes to the computer.

  The other thing that's kind of wired is that the original USB tail does not work when reconnected. That is to say that, out of the box this cable worked, but sans all other mods, this cable when re-soldered to it's original connections will not go.

I'm just baffled at why I can't get 2V to flow. I feel like the computer allows 2V to flow over that connection when it thinks that it is connected to an apple device, or a legit device, I need a way to trick it.

Thanks for the help,

-P


http://scokes.files.wordpress.com/2008/10/ipod-composite-av-cable.jpeg
http://blog.makezine.com/archive/2008/07/diy-iphone-charger.html

 
 
pittsburgh said:
I'm modding radios with apple AV cables, see link below, so that you can play your iphone/ipod through an old radio. I've done this by purchasing apple AV cables, cutting them apart, and hooking them up on the inside of the radio.

  I'm having a problem with charging/syncing. I cannot get 2V DC to flow over the data + pin of my USB connection. This is for use with charging an iphone. The 2V data + USB pin allows data to be transferred to and from the ipod allowing for charging and syncing when connected to my computer. The other voltages check out, 5V, 0V, and 2.7V over the data - connection.

  As a test I bypassed my computer's USB port and went straight to an apple outboard charger. This works every time. I've checked audible continuity between the final connection the end of the AV cable and the USB A connection that goes to the computer.

  The other thing that's kind of wired is that the original USB tail does not work when reconnected. That is to say that, out of the box this cable worked, but sans all other mods, this cable when re-soldered to it's original connections will not go.

I'm just baffled at why I can't get 2V to flow. I feel like the computer allows 2V to flow over that connection when it thinks that it is connected to an apple device, or a legit device, I need a way to trick it.

You might wish to actually read the USB spec.

When using a USB host port (type A) as a charging port, current to charge something is not sourced by the data lines (D+ and D-). Ask yourself why this would be the case.

The VBUS line is the voltage source from which the device being charged pulls current. The resistors shown in the Makezine blog set the voltage on the D+ and D- pins to voltage levels that make the device (the phone) think that it's connected to a battery charger and not a proper host.

Anyways, the schematic shown in the Makezine blog post is pretty clear.

-a
 
  If those are the voltages to make the iphone think that it's connected to a charger, do you have any idea what the voltages are for the sync function?
 

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