This circuit was found in an American magazine 73 for radio amateurs of the 80s. It is an automatic transmission circuit for telegraphy. The circuit is TTL.
This oscillator circuit is from a Radio Electronics magazine from September 1960. The frequency depends...
This circuit uses a piezoelectric tweeter to emit a powerful continuous sound above the audible...
Found in an English documentation from the 90's, this circuit makes slow logical pulses audible,...