This longwave signal booster circuit was found in the 1995 Encyclopedia of Electronic Circuits Volume 5. Note the dimensions of the board. The transistor is a general-purpose transistor.
This circuit activates an output, which can be a lock, only when a card containing the programmed code...
Found in an October 1992 Radio Electronics magazine article, this circuit generates a low-power tone in...
Found in a manufacturer documentation from the 90s, this circuit makes use of period components. The...