This circuit, based on a 555, was found in a Popular Electronics from the 90s. The circuit has the frequency determined by R1, R2 and C1.
This counterphase circuit is from a 1973 publication, and can work with mains voltages or 12 V....
This circuit can be used to directly control direct current loads or higher alternating current loads...
The acquisition of data, from a transducer, so that these data can be converted to digital form...