This circuit was found in an American publication from 1965. The circuit uses components from that time. No information was given about the excitation transformer. Observe the high input power.
This filter that rejects determines frequency (notch) was found in a Popular Electronics of 1993....
Found in an Elektor from the 90's, this double door-bell drive circuit switches a relay by...
Using a 555 this circuit was found in old documentation, but it is still valid. | Clique na imagem...