i have a signal from a sensor between (4ma and 20ma) and i make a resistor (250hom) to get a voltage between (0v and 5v) When i use the analogRead, the result is not stable ??? i have many values swiching between 0 and 1023 despite the sensor conditions are the same.
Zero should never occur, it indicates a broken cable. Did you connect Gnd as well?
Sounds like a floating input.