how to construct a simple circuit using LDR and transistor?

materials: LED, LDR, BC337 transistor, 10k trimmer, 500ohms resistor.. 

Not sure what you want, but the attached picture shows what I might build out of that junk.
In a slightly different version, the LDR and the 10K trimmer switch places. That way the gain is negative. So the LED turns on brighter when the LDR is dark, and the LED turns off (less bright) when the LDR is illuminated.
cc675 years ago
you can use phototransistor instead of LDR. It is more simpler and more fast acting.You don't need any transistor for the circuit. Connect positive polarity of the battery to the collector of the phototrans then connect a resistor and then the load. If it dosn't work... connect the negative portion of the load to the resistor which is connected to the emmiter.
visuallabs5 years ago
Hey We Will Make A Kit On The Some Thing
Here Is The Schematic:

Here Is The Board Layout: