We found this circuit in a documentation from the 90's. Information on the A/D converter was not given but types can be used according to the application.
This linear oscillator was found in a 1968 publication. The operational amplifier is from that...
This circuit was found in Radio Electronics from May 1965. The SCRs and transistors are from that...
This Wien bridge circuit, using a 741 operational amplifier, was suggested by Texas Instruments in its 1996...