Posted in Arduino Hacks, Microcontrollers Tagged adc, analog voltage reference, aref, voltage divider ← Using A Chicken As A Steadicam RC Plane Built Using Pieces Of An RC Car → ...

That reference is by default the supply voltage line for the chip. This should be 5V but will only be as accurate as the regulator supplying it.

“If you wish to use the module as stand alone, you can connect the OLED and a geiger on the + and OUT pins, 5V supply from a battery (voltage regulator NOT included) and you can see the voltage ...