Could anyone tell me how I can design a mains light-on indicator to fit into the back of a standard light switch plate. I would like an L.E.D to flash every second and a beeping sound every 5 minutes while the mains light is on.
You can use anything you like to generate delay and tone signal.
It doesn't have to be 555. Actually I don't really like 555 because
of pin arrangement. You can use TTL or CMOS chips...
Maybe you prefer bipolar transistors? Maybe UJT or PUT?
Or microcontroller?