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.
In the figure we have the way to connect 6 solar cells in order to obtain higher voltage and...
This circuit has a maximum frequency of 10 kHz and a linearity better than 0.01%. The circuit is...
This circuit was obtained in a 1961 magazine, but it can be easily assembled today, as the...