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.
This timer circuit uses a unijunction programmable transistor. The time is given by the capacitor and...
This circuit identifies the holes in a card with 8 bits of definition and was found in a 1995...
This simple circuit with LDR was found in the Radio Electronics magazine of July 1992. Any...