This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This circuit is from a 1976 publication. The circuit formed by L1 and C1 must be designed...
This interesting circuit found in an Elektor from the 90s controls loads in four quadrants of the driving...
This third-order Butterworth filter was found in American documentation from the 1980s. Formulas for...