This document describes a circuit using an LDR, LED, and 555 timer IC that functions as a dark detector. When light falls on the LDR, its resistance is low and the LED does not turn on. However, when it is dark, the LDR's resistance increases, triggering the 555 timer IC to glow the attached LED, indicating that it has detected darkness. The key components, circuit diagram, working procedure, and conclusion are discussed to explain how this simple circuit allows detection of dark conditions.

1. Dark DetectingDark Detecting
LED usingLED using
LDR andLDR and
555 Timer IC555 Timer IC

2. Introduction
Components
Discussion about key components
Circuit diagram
Working procedure
Discussion
Conclusion
Contents

3. 1.LDR
2.LED
3.555 TIMER IC
4.RESISTORS (1k,4.7k,47 k ohm)
5.CAPACITORS(1 nf,1uf)
6.BATTERY(9V)
6. AND SOME CONNECTING WIRE

4. 1.555 Timer IC

5. LED

6. LDR

7. Circuit

9. Discussion
1.The circuit diagram of dark detecting LED. This
circuit shows how we can convert a simple astable
mode circuit to a “dark sensor”. We just need to add
an LDR and a resistor in the circuit, then it simply
works as dark detector.
2.A general purpose LDR is used for sensing the
light.
3.When proper light is falling on the LDR its
resistance is very low.

10. 4.When there is no light the LDR resistance
increases.
5. At this time the IC is triggered and glows the
LED attached with the circuit.

11. conclusion
555 Timer is a highly stable device for generating
accurate time delays or oscillation. Additional
terminals are provided for triggering or resetting if
desired.