Low battery indicator circuit 9v portable#

Now instead of waiting for the battery to deplete itself I am using a lab dc power supply which can output from 0-30V.

Low battery indicator circuit 9v portable#

I am using an Arduino Nano and want to make the project portable using a 9V PP3 battery. Apart from using the 9V battery I use DC power supply. I have attached the circuit I have followed as well. No matter the limit the LED does not blink. I thought it would be pretty easy to detect a 0-5V change from the A0 pin but the 10-bit value it is measuring after removing USB seems mysterious even though I wrote in the code if the voltage drops below a certain level it should start blinking an LED indicating low battery.

The Nano brownout voltage is at 3.8V for me as at that voltage it stops working. Well, everything works fine until I disconnect the USB then the Nano seems like ignoring the voltage I am applying whether it is 10V or 5V or 3V. While the Nano is getting power from both the USB and the power supply I know it favors the USB but I can get the voltage drop form A0 using a voltage divider to read the voltage drop from 0-5V which would results a reading of 0-1023 on the Nano. I am taking the necessary precautions such as not using too much voltage or current which could damage the board however the problem here is everything seems to be working fine if the Nano is connected to the computer via USB plus getting 9V power through Vin. Hello, I am having trouble in a mysterious way.