variable resistor. You can also increase the number of LEDs by simply connecting in parallel with the 390 ohms resistor, or you can connect two or three LEDs in each series with a suitable current limiting resistor. If you are using 3 LEDs in one series then it will be essential to operate the circuit with the voltage minimum atleast 9V.
A Here is an interesting project of a dark activated buzzer & flasher using 556 IC. 556 is a dual timer IC contains two 555 timer ICs in one package. The circuit will blink an LED and beep the buzzer when there is no light on the surface of the LDR. The sensitivity of the dark sensor can be adjusted with the 20K
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