100 Hz Second Order High Pass Filter (CB25815E)

This filter with the 741 op amp was found in the February 1995 Electronics Now magazine. The power supply must be dual.

Notch Filter (CB12169E)
This filter that rejects determines frequency (notch) was found in a Popular Electronics of 1993....
Double door bell (CB7559E)
Found in an Elektor from the 90's, this double door-bell drive circuit switches a relay by...
Sine to square converter (CB7329E)
Using a 555 this circuit was found in old documentation, but it is still valid. | Clique na imagem...