Audio Controlled Switch (CB21262E)

This sonic relay or vox was found in a Popular Electronics from the 90's. The power MOSFET can be of any type determining the controlled load.

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Audio Frequency Counter (CB21054E)
This circuit was published in Popular Electronics from the 90's. The components are common, as...
Electronic Target Shooting (CB18173E)
This circuit is from a 1982 documentation. It can be modernized using LEDs in series with 470 ohms...
PLL CMOS siren 4046 (CB19085E)
The CMOS 4046 integrated circuit is not very common today, consisting of a very efficient PLL for...