Powering Bela with an external power source
You can power Bela from an external 5V DC power supply either with a micro USB cable or a barrel cable (5.5mm x 2.1mm), with the negative voltage outside and the positive voltage inside ("tip positive").
Note, that the internal power amplifier which drives the speaker outputs (on the Bela cape only) is powered only when the barrel cable is in use.
On the Bela cape, connector J1 (not populated by default) can be used as an alternate means of supplying power to the speaker amplifiers. Pin 1 of J1 is connected to the same pins on the BeagleBone Black as the barrel connector (P9, pins 5 and 6).
J1 provides a way to power the speaker amplifiers on the BeagleBone Green, which does not have a barrel connector. Alternatively, by desoldering ferrite bead FB4 from the Bela cape (located right next to J1), the speaker amplifiers can be powered from a separate supply to the rest of the BeagleBone.
Important: only 5V power supplies of the correct polarity should be used with the barrel connector or J1. Connecting more than 5V to the barrel connector, or connecting the supply backwards, may destroy the BeagleBone Black and the Bela cape.
You can connect an external 5V power supply between one of the GND pins and P1.01. See here for more details.
The PocketBeagle comes with support for LiPo batteries. On P2 header Pin 14 (labelled BAT+ at the back of the PocketBeagle) is the positive input for a single cell lithium (lion/lipo) battery. P2 Pin 15 (labelled GND) is the battery ground.
In order to switch on Bela it is necessary to connect P2 Pin 12 (labelled PB) to GND and then to disconnect it, like a switch. This is acting as the main button on the PocketBeagle and is a good place to attach a master power switch if you are embedding your project.
The data sheet lists a supply voltage for the battery input as between 2.75V and 5.5V. We have tested some common 3.7V LiPo batteries like these and they work great.
If you want the LiPo battery to recharge while the board is powered over USB, you additionally have to connect a 10k resistor between P2.15 and P2.16. To check the battery is charging:
- run
i2cget -y -f 0 0x24 0x03to check the PMIC charging status via I2C - output should be 0b0001000
- see PMIC datasheet for more info: http://www.ti.com/lit/ds/symlink/tps65217.pdf
More details here.
The 4.4 Linux kernel that comes with Bela image ≤ v0.3.6b does not fully power off the board when shutting it down. Wait for the upcoming 4.14 kernel release for this to work properly. In the meantime, you may want to add a physical switch to turn off the battery, or briefly disconnect it upon power down.