John I presume your parts kit will be less the actual HC-SR04 detectors, and likely the relays, since there are two options there. Did I get that right? Is everything else on the BOM included?
Also I am not clear on how two of these are interconnected (or if they are) so that the signal goes red on block entry and green on exit? How does that work?
Stan I love that transparent P-51 Mustang model. Sure wish I had known about that back in the day. I am a big fan of warbirds and in particular the Mustang; the perfect marriage of American airframe design and the ubiquitous British RR Merlin V-12 water cooled engine. Always would have loved a flight in one, but alas the remaining airworthy examples are all in the hands of rich warbird collectors I guess. Very neat to see (and hear) them at airshows though. Sigh..... Sorry for digressing. 
Rod
