I have the following circuit which was running for a long time but at one point something broke and it started producing high values such as 4133 or 30412.
I used the recommended 10K pulldown resistor, although some other guides recommend 100k this setup was working for me for a long time.
What I use LDR is an unknown brand, something cheap chinese what you can pickup for arduino kits so I checked a generic data sheet:
Cell resistance 1000 LUX 400 Ω 10 LUX 9 kΩ Dark 1 MΩ
My measurements show something similar. If I put my finger on the LDR the dark resistance is around 0.3 Mohm and when I point a strong flashlight to the LDR the resistance goes down to about 800 ohm which seems to be normal for me.
While the circuit was working properly it always produced values from 0-1023 and dark usually meant under 200.
What can cause this?