Submitted by: Robert M. Carter (robertmawsoncarter@gmail.com).

Not only is it that time of year again but Elektor have a great tradition of Christmas light novelties! Here's my own contribution…

I don't know about you but in my house we seem to get more and more of those LED battery light strings every year and changing batteries/turning them on and off can become a chore. Battery replacement can be made far less frequent by using D cells instead of AAs (D's were a bit big for the photo though) but while we're at it why not make them completely autonomous with a simple timer circuit?

I thought I'd do this with some old-school technology that was lying around in the bits box. Remember the PIC16F84? You could call it “the Arduino of the 90's”, but actually they're still available, cheap and easy to program! The circuit is kept as basic and easy as possible and a simple arrangement of 2 push buttons and two LEDs is used to set the current time. Lights are then switched on at 16:00 and off at 23:00. Simple.

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