The circuit is from 1994 National Semiconductor documentation. The component is not easy to obtain, but there are equivalents that can be searched.
The circuit shown by the figure below can produce signals in the range between 20 kHz and 30 kHz....
We found this circuit in an article in Electronics Now magazine from November 1997. The circuit uses...
The figure shows how to implement an OR function with two inputs, using a relay. The relay...