This simple neon lamp oscillator produces a 140 Hz, 40 V peak-to-peak signal. The frequency is given by the capacitor that can have its value changed. Note the high supply voltage.
This simple intercom for home use was found in a 1979 publication. It can be easily mounted with...
This circuit was obtained from American documentation from the 1990s. The transformer can be a car...
This wired intercom circuit was found in an English publication from the 80's. The integrated...