St. J Wireless Codegraph

This item was produced as an aid to learning Morse code. It was patented on August 13, 1912  (US patent 1,035,257) to Thomas M. St. John of New York. It consists of a nickel-plated brass plate mounted on a wood backing, with a binding post on the upper left-hand corner. Areas of bare metal were exposed to form the code characters, with painted areas providing electrical insulation. The device was used with a battery and buzzer, and transmitted characters were formed by dragging a metal stylus across its surface to make and break electrical contact. Note that the first line (A-G) has a separate metal strip applied over the original line. This was to correct an error for the letter "C", which was originally specified as    dash dash dot dot (_ _ . .), then corrected to   dash dot dash dot (_ . _ .).

In questo link sono elencati 5 modelli, di cui 5 con immagini e 0 con schemi.
Elenco delle radio e altri apparecchi della St. John, Thomas M.; East Windham, NY