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.
The frequency of this oscillator is given by the coil and by C1/C2. The circuit supports any...
This 9-pixel circuit has been implemented with 9 LDRs and can be coupled to a processing system for...
This control circuit was found in a Radio Electronics from May 1965. The circuit switches a...