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.
The integrated circuit used in this 1987 project is not very common these days. However, if found...
This 1-transistor reflex receiver was found in a 1963 publication. The coil is for the mid wave...
This circuit uses a complementary unijunction transistor that is not the common type. The...