Found in an Electronics Now from the 90s, this circuit appears elsewhere in this section and website. The diodes are for general use and the basic frequency is given by C.
In the figure we have the way to implement a voltage doubler in a simple source. The component values...
This circuit, which has a power of a few tens of microwatts, is suggested by Maxim. The circuit has a...
With the name of detectaphone, we find this circuit in a documentation from 1966. It will be...