This driver for audio signals using the TAA435 integrated circuit was found in Philips 1968 documentation. The integrated circuit is difficult to obtain today.
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...