Word Compressor with Gain Control (CB19997E)

We found this circuit in a documentation from the 70s. The circuit uses amplifiers from the time, but it can be implemented with modern equivalents.

| Clique na imagem para ampliar |

Dual indicator (CB22136E)
Obtained from an English publication, this circuit actually needs a current limiting resistor,...
Sound Strength Meter (CB18106E)
This 2003 circuit serves to digitally show the intensity of a sound captured by a microphone....
Audible voltage indicator (CB21332E)
Suggested by a Popular Electronics from the 90s, this circuit uses a buzzer to indicate the...