§ LDR+555: Dark Sensor

Component used:

1)        9v Battery with cap

2)        ON/OFF Switch

3)        L.D.R (Light Depending Resistance)   

4)        I.C 555 with Base

5)        L.E.D (Light Emitting Diode) 5 pieces.

6)        Variable Resistance of 50K ohms

7)        P.C.B (Printed Circuit Board)

This circuit uses the inbuilt comparator of 555.LDR is a special type of resistance whose value depends on the brightness of light which is falling on it. When light falls on the LDR then its resistance decreases which results in increases the voltage at pin2 comparator compares between the input voltage from pin2 and 1/3rd of the power supply voltage. When input falls below 1/3rd then output is set high otherwise set low. When light falls on LDR its input voltage rises so we get 0 volt at pin 3, besides in poor light we get positive output at pin3 to drive LEDs.

Circuit Diagram : design the circuit using PCB-WIZARD.

PCB:

normal

real world

artwork

unpopulated

NOTE: We can also use LM358 or LM324. These are comparator ICs.

LM358 pin details

Circuit Using LM358

real world

artwork

                                                                                                                                              ~pg