On Mon, May 23, 2011 at 7:29 PM, Olin Lathrop w= rote: > Yigit Turgut wrote: >> Ok, forget about the pot, I connected a LDR (2 pins) connected in >> series with 1.5v battery to analog input and conducting the same >> configuration again, but as light hits the LDR, there seems to be no >> change in the input voltage which it should have been. > > The PIC A/D has very high input impedance. =A0You can consider it infinit= e for > your purposes. =A0That means there is no current thru the resistor, and > therefore the voltage at both ends is the same. =A0You might be able to s= ee > this if you draw a schematic. > > Connect one end of the LDR to Vdd and the other end to the PIC A/D input. > Then connect a separate resistor between the PIC A/D and ground. =A0The v= alue > of this resistor should be about what the LDR is in medium light. =A0The = PIC > will read a high voltage in bright light and low one in dark. Works very fine, thank you. I guess sensitivity of LDR will be optimum at the exact middle point (a resistor at exact middle impedance of LDR connected). Is it any different than driving a NTC thermistor ? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .