USB vs External power

Hi Group;

After reading all the discussion I seem to have generated about battery capes, etc.

I have a question / problem.

My project connects to an Alpha WiFi adapter which requires that the ‘Bone be externally powered.

I have an external power supply which works perfectly.

Here is my problem:

As soon as you plug the Bone into a laptop, it starts to boot immediately, because it is running off the USB power.

You get weird errors, or the Alpha is just not detected, until you apply external power.

This is a real pain in the ass, because you cannot just leave the Bone connected to the Laptop and turn external

power on and off. Like you would with say an external hard drive.

I could just cut the power (red) wire to the console, but I am wondering if there is a more ‘elegant’ way ?

Thanks;

Bill

________________________________________
From: beagleboard@googlegroups.com [beagleboard@googlegroups.com] on behalf of William Pretty Security [bill.pretty@xplornet.com]
Sent: Friday, January 25, 2013 7:24 PM
To: beagleboard@googlegroups.com
Subject: [beagleboard] USB vs External power

Hi Group;

After reading all the discussion I seem to have generated about battery capes, etc.
I have a question / problem.

My project connects to an Alpha WiFi adapter which requires that the ‘Bone be externally powered.
I have an external power supply which works perfectly.

Here is my problem:

As soon as you plug the Bone into a laptop, it starts to boot immediately, because it is running off the USB power.
You get weird errors, or the Alpha is just not detected, until you apply external power.

This is a real pain in the ass, because you cannot just leave the Bone connected to the Laptop and turn external
power on and off. Like you would with say an external hard drive.

I could just cut the power (red) wire to the console, but I am wondering if there is a more ‘elegant’ way ?

Thanks;

Bill

What OS are you running on the laptop? Check and see if there are any applications or processes that could be sending serial data to the USB port, as that acts as the console port on the BeagleBone for U-boot interaction. I've had this issue with Ubuntu where an autodialer application (included with the default install for some weird reason) would attempt to send AT commands to the serial port assigned to a USB connection, thinking that it was a modem being attached. The U-boot process will stall if it receives what it perceives to be keyboard input (which is likely an errant process sending junk to the console on the BeagleBone).

Thanks Greg;

I am running Windows Xp with the FTDI virtual serial port driver.

The problem is that many computers will provide power even when off if the device was connected when the computer is shutdown. If you were running Linux you could solve this problem with udev rules. If you stick with windows your easiest course of action is to just plug in the Alfa later after the external power is connected. Btw, you might try turning down the transmit power on the Alfa unless you need it higher, at least initially. They really suck power which can lead to what you’re seeing without external power.

________________________________________
From: beagleboard@googlegroups.com [beagleboard@googlegroups.com] on behalf of William Pretty Security [bill.pretty@xplornet.com]
Sent: Friday, January 25, 2013 8:40 PM
To: beagleboard@googlegroups.com
Subject: RE: [beagleboard] USB vs External power

Thanks Greg;

I am running Windows Xp with the FTDI virtual serial port driver.

I would start by sniffing that USB connection to see what's happening between the host PC and the BeagleBone.

http://www.pcausa.com/Utilities/UsbSnoop/default.htm (Windows XP only)

There is also a USB sniffer floating around out there for the BeagleBone if you have an extra BB laying around to bridge the host PC to BeagleBone connection, although I think that became a commercial product so the source might not be available anymore.

It sounds like something on your host PC is halting the BeagleBone's U-boot process before the kernel gets instantiated.

It sounds like something on your host PC is halting the BeagleBone's U-boot process before the kernel gets instantiated.

Hi Bill,

I don't have a BeagleBone. With that said, I am wondering if you also installed the software driver for the Alfa on your Windows XP host, or if Windows Update automatically downloaded the driver for you? If the Alfa driver is installed, I wonder if it might be trying to send data to the BeagleBone like Greg is suggesting.

Thanks

Bob Cochran

Hi Philip;

I think that this must be my problem. (The computer is providing power)

What I was wondering is if there is a ‘Reset’ line that I could hold low or high until external power is applied ?

That way the Bone would stay in reset until the power is turned on.

Basically what I need here is a black box with a Bone inside and an On/Off switch.

Thanks everyone for the help

Bill

The problem is that the computer will always provide 5V to any connected USB device so that it can enumerate it. I think you can safely cut the 5V wire on the USB wire. I know this is probably not what you want to do, but I don’t know of a way to make the bone not power up through the otg port.

Thanks Philip;

The manual says something about a “Power Button” signal on P9:

“PWR_BUT is a 5V level as pulled up internally by the TPS65217B. It is activated by pulling the signal to GND.”

Also, there appears to be a reset signal of some sort:



Pin A10

|

SYS_RESETn

|

  • | - |

Has anyone used these? The power button sounds promising !

Bill

Well essentially you believe that having power over the 5v barrel connector and over USB is causing your Beaglebone to stop booting. But Gerald says in this post that you can have both power connectors connected and alive:

http://comments.gmane.org/gmane.comp.hardware.beagleboard.general/23301

Perhaps the issue is more like: data is going over USB to the Beagleboneand affecting the boot process.

Bob

You misunderstand.

It isn't that the Beaglebone STOPS booting, rather the problem is that the
bone IS booting
when I don't want it to !

I want it to stay in reset until external 5V power is applied.
That way, when it boots, there will be sufficient power for the board + the
Alpha.

Hi Bill,

Yes, I did misunderstand. Perhaps I am still confused.If the core of the problem is to provide enough power for both the Beaglebone and the wifi adapter, why not connect a powered hub to the Beaglebone, and connect the wifi adapter to the hub? A powered hub can supply enough current to the wifi adapter, right?

But let me be clear that I don't yet have a Beaglebone of my own. I might order one soon. I wish you the best of luck in resolving this issue.

Bob

I’ve been looking at the manual and it doesn’t seem like the PWR_BUT is what you want. I did see that the power management chip can be reprogrammed via I2C from the CPU, but have no idea how you would do that without a lot of work. If it works the way I think you might be able to use a switch that pulls SYS_RESET down to ground until the user flips it “on” (disconnect the short to ground) and the Bone should boot up.
Sounds like you might have to experiment with it a bit.

First of all Bob, thanks for the help.

What I have is a self contained system in a black box. The system is powered
by an external ~12V source.
The source can be anything from an automobile to a gel-cell or a
rechargeable battery pack.
The Alpha is permanently attached to the box containing the bone, so that it
can withstand rough treatment.

There is no way to add a hub. Actually that is one of the reasons I changed
from Gumstix to Beagle Bone.
The Gumstix system required an external hub.

I have a prototype cape on order, so what I will do is fool with the PWR_BUT
signal and see how it works.
If all I need is a SPST switch that grounds that signal, then I'm laughing
:slight_smile:

Bill

Philip/Bob;

Thanks guys.

I’ll do some experimenting and let everybody know how it goes J

Bill

Hi Bill,

Your problem is becoming clearer to me now. Good luck to you. I'll be very interested to know how you solved this one.

Bob

You and me both !

Later ...