[SOLVED] My Clap Switch is not working

[vmukul]

I am designing a clap on clap off switch and made the connections as shown in the below schematic but that is not working.

I have found this circuit here and as shown in the video it is working correctly. How do find the problem in my circuit?

 

[schmitt trigger]

Do you have access to an osciloscope?

With no noise, the transistor is always saturated, meaning a low logic level on pin 2 of the 555. This is the opposite way to trigger a monostable.

Additionally, since the mic is DC coupled, the clap must be strong enough for the mic output to go below 0.7 volt. Depending on the mic's sensitivity, this could mean an EXTREMELY LOUD NOISE to trigger.

 

[Audioguru]

There might be a language problem. The microphone is not a "condenser type" and is not a "electric condenser type". Instead it must be an electret type that is a condenser mic with 48V embedded permanently in its electret material. Its power supply through the 47k resistor powers the Jfet in it.

But the base-emitter voltage of the transistor limits its power supply voltage to only 0.7V which is much too low to power an electret mic. But they say the transistor is turned off so its base voltage which is the mic voltage must be 0.5V or less which is really bad.
The horrible circuit should have a 10k resistor powering the Jfet in the electret mic and have its audio capacitor-coupled to the base of a properly biased transistor.

Did you notice in the video NOBODY was clapping? Instead they were smashing the mic with a hammer!

 

[schmitt trigger]

I had not seen the video, AG.
But after watching it you are correct, they are hitting the microphone!!!

Since this is built on a protoboard, most likely it isn't the sound that is triggering the circuit, but an intermittent contact creates a noise spike which does it.

What an awful circuit! The sad thing is that the web is filled with similar situations.

And the OP has disappeared

 

[E-design]

I see this more and more, new users with one or two postings looking for answers. Once they are helped, they do the vanishing act.

 

[betwixt]

Apart from the obvious microphone issue, there should also be a resistor in series with the LED. I assume ground and supply are also connected to the flip-flop, they are shown for the 555.

Brian.

 

[Audioguru]

Texas instruments say that their SN7474 is obsolete and is no longer available. Its recommended output high current was only 0.4mA (a very very dim LED) and it typically does not go to a high enough voltage to light many LED colors.

 

[vmukul]

Thanks everyone for your replies. As I marked this as "Solved", it was the microphone issue. I tried a few until it worked. Though I need to clap very hard to start the circuit.