Serial switch with PIN diode (CB21257E)

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

Micro Power LED (CB15111E)
This circuit causes an LED to flash at a frequency determined by the capacitor. The circuit has an...
Analog frequency meter (CB7918E)
Found in American documentation from the 90s, this circuit can measure frequencies on a linear...
FM Optical Transmitter (CB5269E)
This frequency modulated light transmitter is from a 1990s documentation. The circuit may use...