I am making a circuit which will make an indication when a sudden shadow(Not gradually rate) falling on the LDR.
I start with a circuit named as dark detector which can give indication when bulb is burnt.
Thanks to ericgibbs's suggestion in an old thread,I already make several changes again to my circuit.
Please refer my attachment for any comment.
I add another LED and 680Ω resisitor parrallel with my buzzer since that buzzer minimum voltage consumption is 5V, I wonder it will continue buzz after some time due to 555 timer.
I replace BC108 NPN transistor with 2N3904, because it is cheaper.
For the LDR, is it all the same? I meant operating ways.Because I heard that some LDR operate in different way, resistance will increase when light intensity is increase. Is it exist?
For the 3 pin of variable resistor, I still no idea how to connect it. Cannot get the idea from ericgibbs.Let says the 3 pin named as pin 1,pin 2, and pin 3,where pin 2 is the middle pin.I should connect pin 1 and pin 2 in series, then connect the circuit with 1 end at pin 1 and pin 2 which are connected by a wire,the another end at pin 3, is it correct?