This circuit is intended for underwater communications. Of course, the critical point is the shielding to avoid water. The circuit is from an Electronic Hobbysts Handbook from the 90s.
This 3V-only circuit was found in old American documentation, but can be implemented with...
The output voltage of this circuit, which can regulate the current in a load between 0 and 1 A,...
This circuit was found in a Popular Electronics from the 90s. The circuit has temperature...