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.
Found on an 80's Elektor, this circuit uses common components, being the diode a general purpose...
This 1.6 GHz oscillator with 40 mW of output power was found in a Popular Electronics from...
Found in a 90’s Popular Electronics, this circuit uses two CMOS inverters to generate a signal of...