We found this code key or coded keyboard in a publication from the 90s. The circuit uses components that are still common today and is powered by a 12 V voltage according to the relay used.
This circuit delivers at its output a voltage that proportional to the amplitude of the input...
This circuit generates signals with opposite phases determined by C1 and adjusted by R2. The...
In the diagram from the November 1999 Electronics Now magazine we have the way to improve both the...