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.
Figure bellow shows a ring oscillator using five inverters of a 4049. [The circuit operates only...
This circuit, which can also be used with flashing LEDs as long as they have in parallel a charge...
June 2017 - The new TE Connectivity FSJMI series of illuminated tactiles switches is now available in Mouser...