This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is 1000 M ohm.
I found this circuit on a December 1976 Radio Elettronica. The Italian magazine no longer exists, but...
CHANDLER, Ariz., June 14, 2017 — New PIC32MM “GPM” microcontrollers (MCUs) are now available from...
This circuit for professional telegraph handlers automatically produces points and dashes. The...