We have described a sound operated switch circuit which will switch ON the light by just listening your clap sound. Another advantage of this circuit is that you cannot get any electrical shock as we did not have to use any mechanical switch.
The circuit is based on two IC: operational amplifier LM741 and JK flip-flop based CD 4027. An op-amp produces an output voltage that is hundreds of thousand times larger than the voltage difference between its input terminals .CD4027 is the master slave JK flip flop IC which work in toggle mode. Here, this IC can be used to change the state by signal applied to one or more control inputs and will have one or two outputs. CD4027 has four inputs namely J, K, Set and Reset and it contain two output namely Q and Q bar(Q not).
The sound operated switch circuit comprises of Operational amplifier A741 used as a sensitive voltage comparator, Mic , Preset VR1 which provides reference voltage to the non-inverting terminal pin 3 and Mic and R2 is connected to inverting pin 2 of IC1 and few more components.
In absence of sound, device remains off as a result pin 2 of IC1 goes high. Consequently output pin 6 of IC1 remains low.
As soon as anyone claps, pin 2 of IC1 goes low in comparison to pin 3 of IC1 and pin 6 become high which provide a clock pulse to pin 13 of IC2 which is a flip flop and stage of flip flop is control by the logic level present at J and K input with some internal control. Change in state occurs at positive going transition of clock pulse. In this set and reset pin are independent of clock and they are initiated when a high signal is present on any of the input pin.
The circuit is triggered on the leading edge of the switch pulse means that output changes when you again clap. From the circuit you can see that both J and K are connected to high input means at every negative or positive transition the clock pulse pin 13 toggle between high to low. This can be verified with the help of truth table of JK flip flop. Therefore, when it receive the clock pulse from IC1 due to clap sound transistor connected to pin15 stats conducting and we will receive the output with the help of relay hear we have connected a LED also so that when there is no AC supply available in that case also you will get some light to see the nearby object. One can adjust the sensitivity of sound with the help of VR1.