I recently purchased from Olimex a single board computer. The board type is OLinuXino A20 Lime 2. The board is installed in the black box that was available from the website. It is connected to the EU-standard power supply adapter, also available on the same site. The Ethernet is also connected.
I hesitate to interface with the device through the USB-OTG cable because the USB connection usually supplies some power through the cable and I have read that some development boards, like Teensy 3.2, can suffer an overload when the adapter power and USB power are connected simultaneously. Is it safe, in case of OLinuXino A20 Lime 2, to connect the USB and the power supply adapter at the same time?
There is no problem to connect a cable to the mini USB while having the main power supply connected over the power jack. Furthermore, you can also have a battery attached at the same time. So it is ok to have a battery, USB cable and battery connected simultaneously to the board. There are transistors that take care of which voltage to be the main source of power.
Notice that the board shouldn't be powered via the GPIO headers. The +5VDC and +3.3VDC lines available on the GPIO and LCD connectors are only outputs.
I also want to interface with the board via the USB-OTG Port. The board ist powered with the 5V Standard Power-Adapter (also bought from Olimex). Now I read in the file A64-OLinuXino-quick-start.pdf the following warning:
QuoteThe A64-OLinuXino board CAN NOT and SHOULD NOT be powered via the micro USB connector
"USB-OTG1", nor via type A female USB connector "USB1", nor via any of the "GPIO1" pads, nor via
the "UEXT1" pads, nor via Ethernet connector "LAN1", nor via "HDMI1" connector, nor via "HSIC1"
pads, nor via nor "IPS1" pad, etc.
How can I even prevent power from flowing to the USB OTG connector when I connect the board to a computer's USB port? Doesn't the USB port of the computer always send power as well? Because of the warning in the manual, I'm now worried that I could ruin the board with a connection to USB-OTG port.
No worries. When external power supply is present powering from the USB is disabled. You can have all these applied at the same time without any risk of hardware damage:
1. Power jack
2. USB
3. Li-Po battery
Thank you!