This circuit for very low frequencies was found in an American documentation from the 90's. Transistors are for general use and the frequency depends on C1 and C2.
This circuit with variable capacitance diode (varicap) is from a publication from the 90s. The...
With this circuit it is possible to divide the frequency of a rectangular signal by values between 2...
The presented circuit uses an optocoupler to trigger a triac. We found it in a Popular Electronics from...