This low power circuit was obtained from an American 80's documentation. The circuit indicates the voltage of a battery being trimmed by the trigger point. The transistors can be the BC549.
This oscillator, from an old Argentine publication from 1973, uses the inductance of the 500 ohms...
This circuit consists of an adapter that allows the reading of low currents at various scales. A...
This circuit was suggested by Philips in an old publication. The coils, made with wire 14 to 16...