In the power circuit there is a comparator that detects the presence of Vin and controls a FET switch in the USBVCC circuit.
I was hoping to connect this comparator to an I/O pin to allow the Arduino S/W to detect Vin. However experiments showed the output of the comparator (on two Elegoo PCBs) wasnt changing when Vin was inserted/removed. It was always 3.3V so the FET is always off.
It appears the potential divider resistor RN1B isnt correctly grounded on the PCB layout. The GND plane stops short of Pin 7 on the resistor pack RN1.
I include PCB layout and photo of the PCB marked up with arrows showing the the area I am talking about.
Is this a known bug?
When powered by USB only the Arduino still gets power but its via the body diode rather than the FET itself. The PCB fault means that (with Vin unconnected) pin 3 of the comparator is floating so sometimes the FET is ON and sometimes OFF and the Arduino power supply voltage varies by +/- the forward voltage drop of the body diode.
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