I'm working on a project where the Arduino UNO MUST be powered through the 5V pin. Is it still possible to print to the Serial Monitor (or another serial console) by connecting the Arduino to the computer with a USB cable?. If not, would an FTDI USB-to-TTL (or another) adapter cable that connects to the Rx and Tx pins work?
A regular USB cable carries power from the PC so if you can use that sort of cable I don't understand why you MUST power through the 5v pin.
If you don't want to use a regular USB connection then you can easily communicate with the PC using a USB-TTL cable.
...R
With my limited knowledge, I think that you will basically connect two power supplies in parallel when you power through both USB and 5V pin and that is not a good idea.
FTDI cable would be the better bet; it can also prevent the automatic reset of the Arduino when you connect it to the PC (if that's a requirement).
Robin2:
A regular USB cable carries power from the PC so if you can use that sort of cable I don't understand why you MUST power through the 5v pin.
I'm actually not connecting power directly to the +5V pin of the Arduino, but to an application specific shield board that fits into the headers of the Uno.
The board has a voltage regulator whose output is routed to the Arduino +5V header. This board is essential for the project and substituting it would make things a lot more complicated.
sterretje:
FTDI cable would be the better bet; it can also prevent the automatic reset of the Arduino when you connect it to the PC (if that's a requirement).
Sounds like I should stick to the FTDI cable. As a follow up question. I'm a little concerned about grounding issues. I want to be able to use a laptop safely to send/receive serial data both when it is connected to mains via the AC adapter and when it is consuming power from its battery.
Power to the +5V pin of the Uno originates from a separate battery that connects to Vin and ground of the shield board I described above.
Is the USB ground on the laptop port connected to the battery's negative terminal?. And is the battery's negative terminal connected to earth ground when laptop is connected to mains?
Scenario 1: Laptop connected to mains via AC adapter and Arduino powered via the +5V pin.
Lets say the Arduino Uno ground pin is connected to the ground wire in the FTDI cable and the +5V wire is left disconnected.
Would I create a ground loop to earth ground? And is it dangerous or would it cause any problems with the signals?
Scenario 2: Laptop consuming power from its battery and Arduino powered via the +5V pin.
Lets say the Arduino Uno ground pin is connected to the ground wire in the FTDI cable and the +5V wire is left disconnected.
Would I create a ground loop to battery negative terminal? And is it dangerous or would it cause any problems with the signals?