This circuit was found in an American documentation from the 80's. The sensor is a special integrated circuit, uncommon in our times. There are modern equivalents.
With the coded activation of the relays, it is possible to control which of the 16 outputs...
The integrated circuit used in this application is not very common. Transistors and resistors...
This simple circuit makes use of neon lamps to indicate the voltage of a power grid. The lamps are...