Here is a traffic light system based on Arduino ... yellow and TF2 is red and yellow The schematic is too easy, all you have to do is connect the leds in series with a 470Ω resistor between the ground ...

Getting an old traffic light and wiring it up to do its thing inside ... Even using one up to show the real-time status of your build or system resource utilization would be pushing it at this ...

But none of them come close to the awesomeness of this traffic light server monitoring system, which has been created using a little Arduino wizardry. The monitor has been created to work ...