This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has several adjustments and uses an operational amplifier. Note the supply voltage.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
This circuit was obtained in an old Elektor. It is a reference, since the integrated products of the...
This circuit was found in a European technical documentation from 1991. It is a circuit that must...