Using the 555 and 4020, this timer was found in the July 1994 Radio Electronics magazine. The relay is voltage-dependent, and the transistor is general purpose.
This circuit is from Motorola's Linear Interface ICs of 1993. The circuit can be powered by...
This circuit activates a relay when the supply voltage drops below the value set in the trimpot. The...
Based on National semiconductor power operational amplifiers, uncommon today, this circuit...