Okay, everything I've tried seems to be overkill for what I want. I need a simple circuit that gives me a logic low pulse about every 20 minutes. The duration needs to be <1 second. It doesn't need to be a perfect pulse though, just something that swings to ground every xx minutes or so (where xx is preferably 10-60 minutes). It should stay high the rest of the time.
Is there something I can "hack apart" in my house that might do this? An alarm clock only goes "off" once per day . . .