I want to use Grbl to control a diy CNC machine. I need to communicate with the CNC using Grbl and this is done via the PC's USB port.
So the PC's USB port is connected to the Arduino Uno which is connected to the shield and the shield and Arduino are powered from an external 5 V power source.
Can someone advise me if this is a power conflict (all grounds are common)?
1 Answer 1
Powering from the 5V pin and USB at the same time should be avoided. This is because the circuit that controls the power from the USB is triggered from the VIN / barrel jack and needs to be above about 6.5V to cause the USB power to be isolated.
It won't damage your Arduino, but there is a chance that your computer may be unhappy and shut the USB port down. 5V shouldn't cause any damage though, but it may detect that something isn't quite as it should be and take steps to protect itself.
One possible "fix" is to take any suitable disposable USB cable and strip some of the plastic outer casing from it (a couple of inches should do the job) and spread out the wire and foil shielding (assuming it exists). Locate the red wire and cut it. Join the red wires together again through a diode (ideally Schottky to reduce voltage drop) with the anode towards the computer and the cathode (stripe) towards the Arduino. This will isolate any reverse power while still providing the USB 5V to the USB interface chip's VBUS pin.