I want to use an old car radio for music on our toilet
It shall turn on/off with the light switch.
Now the problem is, that the car radio requires some power permanently to remember where it left of (or its radio stations).
According to this this thread from 2013 in boot-forum (German), someone has posted a circuit layout that he says he's been using for 5 years successfully now:
Jumping out of an airplane is not a basic instinct. Neither is breathing underwater. But put the two together and you're traveling through space!
I've wired up a prototype setting and: It works! Hooray!
Although: I've substituted the diodes with a diode-rectifier.
I didn't have the proper diodes at hand, and couldn't wait to try it out. Had an old rectifier laying around. Connecting it this way to achieve the same as the above circuit:
Pin-wiring for rectifier instead of 2 diodes.
Jumping out of an airplane is not a basic instinct. Neither is breathing underwater. But put the two together and you're traveling through space!
Hooray!