This circuit was found in the January 1995 Electronics Now magazine. The source must be dual, and a noise pickup guard ring must be used.
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...