This signal injector and tracer (follower) was found in an old American documentation. The transistors can be general use and power is made with one or two common cells.
This circuit was found in RCA documentation from the 1970s. It was suggested to produce tones for...
This simple circuit uses a zener diode and two LEDs to indicate whether the voltage of a power grid...
Found in a 90s documentation, this switch that is also sensitive enough to operate capacitively uses...