This circuit was found in the November 1974 Radio Electronics magazine. The voltage depends on the supply and the timings of R1 and R2 as well as C1 and C2.
To obtain variable frequency signals, the circuit in the figure is recommended. In this circuit, the...
This circuit was found in old English documentation. It can be improved by using resistors of...
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...