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.
Found in a 1970 documentation this circuit makes use of components still common in the market. The...
Found in old documentation, this circuit makes use of amplifiers of the time, uncommon today. Next...
This circuit was found in ancient American documentation. Equivalent operational amplifiers can be...