This simple circuit needs a high gain stage to compensate for losses. It consists of a passive tone control obtained from Electronics Today International of the 90s.
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...