This Texas Instruments circuit is from the 80's. However, it can be implemented with modern operating systems. The power supply must be symmetrical.
This circuit uses a contactor having been found in a 1987 publication. More modern equivalent...
This circuit was found in a 1977 Radio Shack documentation. Its purpose is to generate 1 Hz...
This circuit was found in a 1980s documentation. It decodes by identifying a certain frequency tone...