You can't actually do this the way you describe. You can't pulse the motor outputs as required to drive the FOS with the standard firmware. The FOS has only one LED, and the VLL signal is a bit more complicated than on/off. You can use the scout VLL (...) (24 years ago, 2-Feb-01, to lugnet.technic, lugnet.robotics.scout, lugnet.robotics.microscout)