This circuit was found in the July 1995 issue of Electronics Now magazine. The integrated circuit is an RCA-era type. The triac must be equipped with a heat sink.
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...