Gil,

Are you assuming that a Relay is also driven by the same port as the LED/Switch? Otherwise, i don't understand why the relay is "coupled" to the led/switch port activity.

I assumed a "flip-flop" was not allowed if external logic is ok then the problem get easier to solve.

As to the timer, i think you'll find the LED is somewhat forgiving due to the exponential nature of human perception of illumination so, depending on what else is going on, a "round robin" program loop could work as well.

regards,
p