This sound meter or sonometer was found in a Popular Electronics from the 80's. The circuit can be easily implemented today, and the microphone is made of electret or ceramic.
This circuit generates approximately sinusoidal signals from the rectangular signals generated by a 4093...
This circuit was found in Motorola's 1968 documentation. The SCRs are then replaceable with...
This circuit mimics the sound of a siren when we turn the axis of the small DC motor. The...