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 simple metronome, from 1985 documentation uses only transistors and has two settings. For...
This circuit is suitable for modulating AM transmitters. The circuit is from a 1977 radio amateur...
This flasher was found in an old Hands On, but uses common components. The optocoupler can be...