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 circuit was obtained in Radio Electronics from the 90s. The integrated circuit is uncommon...
This 4-digit digital clock for hours and minutes with CMOS integrated circuits was found in a 1995...
This circuit is indicated to operation with low intensity sources such as electret microphones and...