This circuit activates a relay when the supply voltage drops below the value set in the trimpot. The transistors can be the BC548 and BC558 and the 6 V relay. The circuit was found in a 1999 Poptronics.
This circuit was published in an English magazine from 1977, but it can be easily assembled since...
The maximum current of this circuit is 1 A. The circuit is from Motorola Linear Interface ICs from...
This circuit is a handset receiver that picks up the signal emitted by a coil under the rug or...