well my circuit is a dark detecter. it's when it's dark there is a led that turn on, the circuit is with an ldr. and i would like to put 100 ldr for 100 led, its like if i put only one ldr in dark one led turn on but i dont whant to build 100 circuit so if someone could help me. in think the easy way to understand what i want is that i want 100 circuit in 1 circuit plz if you can help me.
plzzzzz help me i realy need that

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Hey, I can help with this one!!! You want a 741 op-amp, and use the LDR (CAD cell) and another resistor as a voltage divider applied to the non inverting input. Place another voltage divider using a pot on the inverting side. output to a 2n2222 bjt to the led. The phototransistor circuit is the one, usung a LDR instead of the phototransistor. The previous circuits use a lm339 op amp which provides a path to ground as an output. Very limited current though.
http://home.cogeco.ca/~rpaisley4/PhotoDetectors.html
http://www.uoguelph.ca/~antoon/circ/sensor2.htm