Suggested by Maxim in documentation from the 90s, this circuit has its response curve given next to the diagram as well as the formulas for the component calculations.
This circuit was originally used in a 1989 documentation presence simulator. The circuit activates...
This old circuit uses an operational one from the 70s, but it is still useful in current projects. The...
We found this circuit in a Popular Electronics from the 80s. The circuit is based on the LM3909, a low...