This circuit is from an American 80's documentation. The circuit indicates when the voltage of a 9 V battery drops below 7 V. The transistors can be BC548.
June 2017 - New Honeywell MT MICROSWITCH Series can be ordered from Mouser Electronics for...
This circuit for the very low frequency range was found in the Radio Electronics magazine of...
This circuit is from a 1992 publication, but can be mounted very easily today. The circuit is...