This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
This circuit from the 70's used germanium transistors and operated in the range of medium and...
The figure shows how to convert a rectangular signal into a triangular signal using an integrator. The...
This circuit was found in a National Semiconductor manual from the 1970s, appearing in articles and on...