Serial switch with PIN diode (CB21257E)

This circuit was found in a Popular Electronics from the 90's. The circuit is connected in series.

Flame Detector (CB17581E)
This circuit detects the presence of a pilot flame in heating systems by the presence of infrared...
SUS Frequency Divider (CB19903E)
In the figure we have a circuit that uses unusual components, being indicated for low frequency...
Triangular and square generator (CB21449E)
Found in older Signetics documentation, this circuit generates signals from 30 Hz to 25 kHz....