This circuit uses a quadruple operational amplifier of the time. The circuit is from the 70s but can be implemented with modern operators that require the use of a symmetrical source.
This polarity test or indicator indicates the polarity of a power line by LEDs. The circuit is...
This is the circuit of a digital clock published in the January 1975 issue of Radio Electronics magazine....
Found in an Elektor from the 90s, this circuit can be powered directly by the power grid. The...