Found in an American 1980s documentation, this circuit compares signals from two TTL sources, providing an output that depends on the frequency difference. The circuit can be used as a shield.
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...