Mic connected to the pin no 2 of the ic 741 through capacitor .04 micro farad. Here capacitor block the dc voltage and pass only signal to the amplifier circuit. Pin no 6 is the output pin no of the ic 741. Pin no 3 is connected to zero voltage through voltage divider circuit. Here we use two 10 k ohm resistor as a voltage divider components. Two 10 k ohm resistor provide a zero reference voltage to the pin no 3 of the ic 741. Output of the ic 741 is further amplify by the two transistor circuit. Here we use one is npn and second is pnp transistor . Collector of the npn transistor is connected to the positive voltage and collector of the pnp transistor is connected to the negative voltage. Output of the transistor is available on the emitter point and this output voltage is connected to the speaker through one capcitor
Analogue signal from condenser mike is also feeded to the input of the op-amplifier using selector switch. Condenser mike convert the sound signal into electrical singal and this signal is coupled to the pin no 2 of the ic 741 through .04 microfarad capacitor. Resistor 10 k ohm provide a dc voltage to the condenser mike.
Gain of the amplifier or ap-amp is depend on the feedback connec mmmmted to the circuit. In this project we use one 10 k ohm resistor in series with the 100 k ohm variable resistor. With the help of this variable resistor we control the gain of the op-amplifier.
Now whatever we speak or press the switch this data is superimposed on the light of the laser.