We made two RCX robots talk to each other, like old friends.
All traffic lights use the same idea.
Real traffic lights, tell people when they should stop their car. The car waits patiently at amber, waiting for red, then green. The one on the left shows a close up of the three lights. The one on the right shows a shot of just the lights. We also fitted a siren to the the red light, so when it went red, the siren went off, telling people to cross the road.