This experimental telegraphic communication system can have wires connecting to the handset of several kilometers in length. The handset is of the piezoelectric type and the frequency of the emitted tone is adjusted in the potentiometer. The circuit operates with a high line voltage. The transformer has a secondary from 6 to 12V x 100 to 500mA. The circuit is from the book Science Fair Projects by Newton C. Braga, published in the United States.