This circuit is from an old documentation, making use of an operational of the time. The circuit can be adapted to use modern components. The power supply must be symmetrical.
Many reed switches can be wired in series to perform na efficient alarm as shoen in the figure....
Figure bellow shows how many 40293 can be cascaded. The input CI of the first circuit is grounded. The...
The circuit is from 1980s Linear Technology documentation. The components are of the time and...