The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
We found this circuit in the April 1975 Radio Electronics magazine. The circuit has a latch and...
We found this sophisticated home alarm in a 1994 documentation. The circuit supports sensors of...
This circuit was found in the 1991 Electronics Experimenter's Handbook. It activates a relay when...