This circuit has a 2 V full scale using a 4-and-a-half-digit A / D converter. The circuit is powered by a voltage of 9 V. We found this configuration in the 1983 Intersil Databook.
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...
We found this circuit in a 1990 documentation. It works with the power of the digital circuit...
The filter shown in the figure can operate with frequencies up to several tens of megahertz thanks...