I'm using an XBee serie 2 module for sampling the values of three sensors, a photoresistor (LDR) a moisture sensor and a temperature sensor (LM35). When there is no brightness the photoresistor has the maximum value (1023), but if the environment is very very dark the value is the same 1023, but the other sensors begin to be instable giving values greater than normal. Maybe an XBee ADC sampling problem? or could be a circuit problem?
The XBee module I'm using for sampling, use a cyclic sleep mode: it wakes for 100ms and stay sleep for 3 minutes.. I tried to use a greater wake time like 1s but the problem is always there.
This is the scheme:
This is a picture: https://dl.dropboxusercontent.com/u/9029111/IMG_4712.JPG
I think it's a power problem, because if I put a 1Kohm resistence near R2 the moisture sensor is ok, and the temperature varies very little to vary the brightness