Found in a 1980s American documentation, this circuit operates with 5 V signals requiring 55 cycles of 500 Hz for tone recognition. The circuit can be adapted to operate with other frequencies.
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...