I have an old traffic light that I want to power with LEDs and an AC/DC 9-12volt plug-in converter. I know how to do that easy enough, but I want a device that will (when powered on) light the green lite for 8sec, switch to yellow lite for 8sec, switch to red lite for 8sec, then start over at the green lite. I want it to continue to loop until the unit is powered off. I would like to either purchase or build this, or a combination, which ever will be cheaper. I think it can be done with a 555 timer but I'm not sure how. Any ideas? thanks.