Greetings,

When in use, a few of our home theater components heat up the interior
spaces of our entertainment center to a temperature that I feel is too
hot (yes, that's a very subjective statement). The entertainment
center uses tall, mostly glass doors, and they are one-piece,
therefore when they are open they protrude pretty far into the room.
When they are closed, there is little-to-no ventilation inside the
cabinets. One evening, I mustered up some courage and tried simply
leaving the doors open but sure enough, one of my kids came close to
ripping the entire door off of its hinges when she bumped into it.

Now I have a bunch of very quiet 12V computer fans in a box and, being
a long time victim of chronic tinkering disease, I was considering
installing one or two in the cabinet backs to draw hot air out. But I
know that when I am not around, no one in my family is going to take
the extra step to turn on the fans.

So I was thinking of some sort of current sensing switch to energize
the fans when the system was in use, sensing AC current draw over some
adjustable threshold value. I tried a web search and found current
sensing units, but these seemed to be industrial-quality, overkill for
my application, and well, yes, I'll admit it, it'll be more fun to
build it.

I was wondering if anyone had a pointer to a simple circuit I could
build to accomplish this.

Thanks for any help, best wishes.

Apologies if this post doesn't fall under "repair" in folks' opinions
- I suppose it could be considered "repairing" my entertainment
center...