Powering the BeagleBoard through the Expansion Header

Anyone that had tried to produce a kindof closed thingy based on a Beagle has finished up with a bigger-than-expected box or with quite some connectors sticking out the box. The power jack is a difficult one because you always need power.

It is not that much of a problem as you need to connect your board to some kind of power source anyhow, however, for a "better finished" product you will expect things like a power switch and some LED indicator in your project's box (the POWER_ON led on the BeagleBoard is not very useful when you put the whole thing inside a box). Even worst, if your system will run on batteries it is not very aesthetic to see a big barrel connector going out your box into the Beagle power plug.

So, a simple workaround is powering your Beagle through the expansion header (http://elinux.org/BeagleBoard_Hardware_Interfacing#Powering_the_Beagle). Using this solution it is very easy to add a switch and a LED to your box and keep everything neat inside the case.

But before you try this just a word of caution.

First of all, carefully pay attention when connecting your wires. Feeding 5V in the wrong pin can damage your board. 5V go to pin 2 and GND just opposite to 28 or 27.

Second. The barrel connector on the board does something more than feeding the 5V to the electronics. It switches pin 5 on the TPS2141 effectively cutting off the power from the USB OTG port. Please read carefully section 8.2 from the BeagleBoard System Reference Manual (http://beagleboard.org/static/BBSRM_latest.pdf).

To be honest, I had not go that far to know what could happen when plugging something in the USB OTG port while powering the BeagleBoard through the expansion header so, if you are in doubt do not use the OTG port or be sure to properly deal with pin 5 on the TPS2141. Here is a reproduction of the circuit in the Beagle System Manual, with the relevant sections highlighted:

BeagleBoard Input Power Selection CircuitBeagleBoard Input Power Selection Circuit

For the time being I had just added a switch and a LED in a breadboard... The idea is to use this approach for the picoFlamingo (http://papermint-designs.com/picoflamingo) hardware that we are reworking.

BeagleBoard Expansion Header Power. Switch and LEDBeagleBoard Expansion Header Power. Switch and LED

Finally, note that I had just put together the parts and turn on the board, let it boot, then login and switch it off (5 minutes total more or less). I had not been using this approach in a regular basis, so follow this at your own risk.

The LED and switch mod isn't the most impressive thing in the world, but turning the Beagle ON without pushing cables in any socket was quite nice ;)