Is it possible to use a pair of LDRs wired in series as if it were a potentiometer and read the value from the common terminal as the wiper?
If I vary the illumination from one LDR to the other, the reading from the wiper would be seen by the board as if coming from a potentiometer. But as far as I know, when fully illuminated, LDR don't show zero resistance. Maybe I will not get the full 0..1023 range at the analog input?
I know the answer would be a question: "why not to use a potentiometer?" Please believe me, I must use LDRs in tis project.
With two LDRs you will not get the full range. You may also have problems with linearity and balance in sensitivity.
What LDR are you talking about.
You could just use a LDR and an appropriate valued resistor.
If you are not sure, make it a Wheatstone bridge and use an available module with a differential amplifier, to trim the readings to the desired range.
Linearity will not be a problem as it is not required in my project. Anyway some kind of linearity can be achieved by properly shaping the plastic strip that will slide in between the LDR and the LED. I'm not saying that it will be a piece of a cake.
I think your idea would work providing that as the light source over one LDR gets dimmer, the light source over the other gets brighter and they do this to a fine tolerance of differential. Only this way would the LDR arrangement mimic a physical potentiometer, the type that you turn by hand.