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 crystal-controlled oscillator generates a 1 MHz rectangular signal and can be used as a time...
This' 90s circuit emits a signal in the FM band with a few tens of meters in range. The coil is...
This configuration, found many times on this website, is from a 1977 documentation. The frequency...