Voice activated intercom (CB7828E)

This one-channel circuit was found in a 90s Popular Electronics, functioning as a vox. Components are common today.

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Milliammeter Scale Expander (CB4773E)
This circuit was found in a Popular Electronics of the 1990s. Its purpose is to expand the scale of...
Touch Bistable 4011 (CB16943E)
This circuit can be used as an input shield by removing the signal directly from the second port,...
Precision current drains (CB15421E)
In figures 1 and 2 we have two current drains that can be made with operational amplifiers and...