this circuit will make a alarm when the light falls on the ldr
Step 1: Things Needed
1] resistors 100k ohm , 56k ohm , 10k ohm
2] transistors 1 pnp and 1 npn
3] capacitor 0.04 uf
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!!