I am trying to make a clap on switch and have the following schematic.

The dotted box is the electret condenser microphone. I set this up as the first stage for the amplifier design. I would like to fully understand this before moving on to the next stage. The circuit works but I am more eager to understand it, not just set it up and watch it work.

First question: What does the FET impedance converter do?

I have researched and understand that the diaphragm or the back plate is polarized to eliminate an internal voltage source. I understand that the change in capacitance results in a change in voltage. But I do not understand the schematic for this microphone. Specifically what the FET impedance converter does.

Second question: What is the other component inside the microphone?

I read that the other component inside the microphone is a dc current blocking capacitor.


enter image description here

  • \$\begingroup\$ The "measurement circuit" from the datasheet does not represent the internal cicuitry of the microphone. Or rather, not just the internal circuitry of the microphone. The microphone is just the section inside the dotted lines. The rest is external. The whole thing together is how the microphone was connected in order to measure the sensitivity and freqiency response. \$\endgroup\$ – JRE Apr 3 '18 at 4:52
  • \$\begingroup\$ Your "clap detector" circuit likely will not work well. R1 doesn't do anything useful (it just wastes current.) Q1 would short current to ground (if it reacts at all) which isn't a good way to turn off the LED. I'm using my phone, else I'd use the schematic editor to sketch something a little more reasonable. \$\endgroup\$ – JRE Apr 3 '18 at 4:58
  • \$\begingroup\$ Ok thank you. I understand the dotted lines is the microphone. I got this schematic off a youtube video and just want to understand the best way to do this. But first I need to understand how the microphone works. \$\endgroup\$ – Eric33 Apr 3 '18 at 5:01
  • \$\begingroup\$ The circuit you are using is not a good example of how electret microphones are typically used. The way it is connected to the transistor is also not the typical way transistors are used. \$\endgroup\$ – JRE Apr 3 '18 at 5:12
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    \$\begingroup\$ See Electret microphone Wiki for some info about the microphone and a vague idea of what is inside. (Usually, the only active device is just a JFET -- not an opamp.) Then do a search here on EESE for "electret" and you will find good info. I think there are a few links on EESE about clapping, too. So enter "electret" and also "clap" and see what you get. \$\endgroup\$ – jonk Apr 3 '18 at 5:29

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