The operational 714 (not the 741) is an old Raytheon type that is no longer common today. The circuit can be implemented with modern operational. The power supply must be symmetrical.
Obtained from an English publication, this circuit actually needs a current limiting resistor,...
This 2003 circuit serves to digitally show the intensity of a sound captured by a microphone....
Suggested by a Popular Electronics from the 90s, this circuit uses a buzzer to indicate the...