Light Decting Circuit

About: None of your buisness

this circuit will make a alarm when the light falls on the ldr

Step 1: Things Needed

you need-
1] resistors 100k ohm , 56k ohm , 10k ohm
2] transistors 1 pnp and 1 npn 
3] capacitor 0.04 uf
4] ldr
5] 8 ohm speaker
6] 2 cells
7] battery holder
8] pref board

Step 2: Ldr

A photoresistor, light dependent resistor (LDR) or cadmium sulfide (CdS) cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor.
A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.

Step 3: Circuit Digram

solder according to the digram.

Step 4: All Done

you can put the circuit in a box when you open the box in a well lit room the alarm goes off!!



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    3 Discussions


    7 years ago on Step 3

    Please!! We need the values of Components Added to your Diagram..Many Thanks!!


    8 years ago on Introduction

    I'd love to see this in it's finished form -- perhaps a video is in order. Thanks for sharing!

    1 reply

    Reply 8 years ago on Introduction

    the box was just an idea and i am not able to attach the the video as it says it is more than 10 mb