The whistle switch allows you to turn on, or off, an appliance by whistling at it. I originally built the whistle switch in 1974. Do not attempt to duplicate it from the schematic below, but instead, understand the functions and duplicate these functions with more modern components.
The audio amp, after the microphone, should have enough gain to produce square waves from input noise. The LC tuned circuit can be replaced by an active bandpass filter, at the frequency that you whistle the easiest. The detector has a slow attach, fast d