Found in an EDN from the 90s, this circuit makes use of integrated circuits of the time, some of which are uncommon today. The output is given by:
Where:
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...