Mega SDK, no USB power when using external power

Development Tools IDE 1.x
1

Hi All,

I am trying to use the USB on the Mega SDK while powering the board with external power (6x1.2V batteries) (not Vin).
When I do this, the USB is not powered. Is that something I can fix?

Thanks!

2

When you say "not Vin", do you mean directly to the 5v bus? If so, you need to read this thread before trying that again:
http://forum.arduino.cc/index.php?topic=82046.0
...especially this post in that thread:
http://forum.arduino.cc/index.php?topic=82046.msg758170#msg758170

3

No, not to the 5v bus, using the power plug.

4

Then you are ok as far as damage, but Vin or the power plug disables the power to the usb port from the 5v bus. Unless you power the usb through the usb port, it won't have power according to the schematic.

5

Maybe I misunderstood. Do you mean the usb host port? If so, it should get power from the 5v bus if there is enough current to power it.

edit: But I doubt if the batteries will provide enough current for the Mega and the usb host port.

6

Ok, so this is the issue "the power plug disables the power to the usb port from the 5v bus", anyway around it?

7

grund_d:
Ok, so this is the issue "the power plug disables the power to the usb port from the 5v bus", anyway around it?

I don't know if you read my previous post. Are you talking about the usb port that connects to your computer or the usb host port?

If you are talking about the usb host port, it should get power from the 5v bus if there is enough current to power it.

If you are talking about the usb client port that connects to your computer, you need to jumper a FET on the Mega, but I don't recommend that.

8

It is the USB host port, and there should be enough power, got 6 2300mAh AA batteries connected, but the device connecting to it does not turn on (XBOX RECV).

EDIT:It does turn on straight away at the moment I connect the USB port to my computer., when I disconnect my computer the device turns off again.

9

Here is the data on the Mega ADK. You should read the "Power" section carefully. I don't know what the XBOX RECV requires as far as current.

10

Looked into this further seems that with 8,2 V input the LM2736Y only gives +/- 3.2V, verified that R2 and R3 are the correct resistors. Anything else to check?

11

ok ,found it, my board is equipped with an LM2734YMK ( marking shows SFEB), but the resistors placed are for the LM2736 :astonished: (330 and 1K)..... which results in broken board =(

wonder how this could have happened.