This circuit from a Popular Electronics from the 90s uses a common optocoupler and a general-purpose transistor to control a sensitive relay that can be from 6 to 12 V.
Ordinary batteries cannot be recharged, but they can go through a process of "rejuvenation" that...
We found this basic circuit of a relaxation oscillator with unijunction transistor in a 1976...
This circuit, from a 2006 documentation, automatically controls the activation of a water pump, and...