Found in a 1980s German publication, this circuit tests batteries by type. The circuit is based on a range of LEDs of different colors and is given a table with indications for various voltage ranges.
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...