This circuit is from NASA documentation from the 1980s. The circuit shows how to obtain a stable optical coupler system. The circuit can be used as a shield.
This filter for the 300 Hz to 3 kHz range was found in an American documentation from the 90's....
The battery is charged by the photocell that keeps the low consumption beacon in the dark. The...
This is the typical circuit of an FET amplifier stage in the common source configuration. The circuit is...