@jmarcelino It's without ADC (maybe I need to do it with an ADC). It's just a pin defined as input like : pin = Pin('P19', mode = Pin.IN, pull = Pin.PULL_DOWN) pin.value() which gives me a simple 0 or 1 (I guess 1 when the voltage is at least half of the 3v3?). I will check what the ADC version gives me next week (I have no module with me unfortunately this week-end). It might give me the reading I want. Also thanks Robert for your answer, I will have a look into the pin sheets of the module.

@bnjroos I'm definitely not an EE, but you may want to have a circuit where you use both VDD or 3V3 and a GPIO pin as inputs. When VDD/3V3 are off, just ignore completely the GPIO pin (open circuit) and set the output to whatever state you need. When they're on, they you can use the GPIO pin (directly or indirectly) to control the output.