This circuit was found in a 80s American documentation. The zener diodes determine the points of action of each stage and the transistors can be general purpose types.
This contact or reed switch actuation was found in a 1964 Electronic Design. The circuit can be...
This is the previous version, but with a simplification given by the use of the 7404 and 7408...
In the figure we present a circuit of a microphone signal conditioner using the SSM2167 integrated...