Testing LDR

LDR (light dependent resistance) can be very easily tested by using a digital multimeter. We are aware that the resistance of an LDR varies according to the light falling on it .In bright light LDR resistance will be around 500 Ohms and in darkness the resistance will be around                 200 K.Ohm. For a proper testng we need to measure the resistance of the LDR in bright light and in darkness.

Testing in bright light
Keep the multimeter at Resistance checking mode. The LDR must be subjected to a bright light source (day light is enough).Now the multimeter will show a low resistance reading around   500 Ohms.

Testing in darkness
Keep the multimeter at Resistance checking mode. The LDR must be subjected to darkness by covering it with an opaque paper. Now the multimeter will show a high resistance reading around 200K.Ohm

IF both the tests are OK we can conclude that the LDR is working fine

3rd Program

This is a simple program of adding two numbers which are entered by the user

#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int a,b,c;
cout<<"Enter the first number ";
cin>>a;
cout<<"Enter the second number ";
cin>>b;
c=a+b;
cout<<"Sum = "<<c;
getch();
}


Click here to download

2nd Program

This is a Simple program to add two fixed numbers


#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int a,b,c;
a=5;
b=44;
c=a+b;
cout<<"Sum = "<<c;
getch();
}


Click here to download

1st program (Display Hello World)

This program helps to display a line in C++



#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
cout<<"Hello World this is my first C++ Program";
getch();
}

Link to download the Compiled program

Simple Siren using op-amp

Intoduction :-

Device such as burglar alarms and sirens, whose basic purpose is to monitor certain conditions. The above figure shows a simple siren/alarm circuit using a dual-amp MC1458, audio amplifier LM380, and a 1-W speaker. The dual op-amp is used  as a signal generator that produces square, pulse and triangular or sawtooth wave froms.

Operation :-

The A1 and A2 op-amps make up a waveform generator in which the output of A1 is a square wave or pulse waveform and that of A2 is either a triangular or sawtooth waveform. The potentiometer R2 controls the frequency as well as the type of output waveform of op-amps A1 and A2. The switch SW1 connect the output of A1 or A2 to the audio power amplifier LM380, this in turn drives the speaker. Although not used in the circuit of figure 1, a potentiometer may be connected between (+) and (-) inputs of the power amplifier to control its voltage gain, which in turn controls the sound volume. The sound level produced depends on the position of switch SW1, the wiper setting of potentiometer R2, and the value of capacitor C4. Therefore, sound of varying intensities can be obtained by adjusting SW1, R2, and C4.

For higher output power (sound intensities), audio power amplifier may be used in the bridge from. This configuration will also require a higher wattage speaker.

PARTS LISTS :-

R1, R­4 = 10 KΩ
R2 = 20 KΩ potentiometer
R3 = 39 KΩ
C1, C3 =0.1 µF
C2 = 100 µF
C­4 = 0.05 µF
IC1 = MC1458 (dual op-amp)
IC2 = LM380    (audio power amplifier)
8Ω 1-W speaker
SW1 = Three-position switch