This circuit from a Popular Electronics from the 90's can generate signals from 0.03 Hz to 3 kHz depending on the value of the capacitor and resistor.
We found this circuit in an English publication from the 1980s. The circuit uses current...
The circuit shown in the figure can be useful in cases where a common telephone extension is used....
We found this circuit in an American documentation from 1977. The circuit must not be powered by a...