We found this circuit in Radio Electronics from the 90s. The components are current. The sensor is a common general-purpose transistor. The connection to the sensor is made by twisted pair.
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...