This shield circuit is from an American documentation from 1969. The components can be modified according to the relay and power, and the coupler can be of a modern type.
This circuit was found in the magazine of radio amateurs 73 in a 90's edition. The components are...
This circuit was found in a 1974 publication. It converts the applied voltage into pulses of...
This circuit generates approximately 30 Hz signals from a 3.3 kHz clock. The circuit was found at...