Thanks for the help 
My layout is Scoreboard XXX XXX XXXXXAA
YYY YYY YYYYYAA
where each lane has "light gates" setup in 3 locations on the track. In this "schematic" the Ys would be the photodiode, and the X's are IR-Leds lensed to the photodiode accross the 3' track. Groups of 3 allow me to calculate things like velocity and acceleration at various points. The group of 5 is the startline (it' dog racing; they start, do the run and "boxturn" and get a ball, and return, passing nose-to-nose with dog 2/3/4. If any start or pass is early, it's a fault and the run doesn't count. The course is 55' (so a run is 110')
As I don't know how tall any given dog is, each X/Y consists of pairs at 6 different heights (every 4" from 4"-24"). I can get away with running a flat cat-5 from the X-Y under the mat. I don't want to leave the IRLEDS on all the time, just for safety reasons as well as battery power. So yes, I'll be sampling 18/ms most of the time, and when I'm around the startline it'll be 30/ms + some analog sampling for the rangefinders (which I'll sample as often as possible, even though they only update at 20hz, to deal with analog noise/averaging).
The AA's are sharp rangefinders, going from 3'-15'. I'm analyzing how close the "pass" is between Dog A and B, as the dogs move fast enough that one will often still be covering the startline when the other approaches (nose-to-nose passes are sought and often obtained).
I haven't interfaced the two lanes yet. If anything, I'm thinking wired serial/softserial is fine, as I can setup a lot of the equipment between the 2 lanes, so a wired connection's fine. Generally, they don't need to have much if any connection with each other. Right now I have the lanes wired to the light-tree. I'll likely have the lanes not even have any communication with each other, but have each communicate with the light-tree, so I can get start/fault type information that way.
The light-tree (picture drag-racing red/yellow/green/GO lights), hasn't been made to scale yet, but is just a YELLOW/YELLOW/YELLOW/GREEN tower, with red toppers on each side for displaying a fault indicator.
At the end of each lane is a scoreboard. I've found 7" single digit 7 segments, and will use those (it needs visible at ~100'). I'm thinking a simple RF will be fine. Very little data sent to that unit (so it'll be an uno or less). A board for each lane, 5 digits and a fault indicator. A slightly smaller board with 3 digits for showing pass-times.
At one side of the lanes is the "controller". It's got an SD shield and handles all the data crunching. Knows from a database which dogs are running, in which position, and keeps track of all the relevant data from their run, for later analysis. That one will have the real UI on it. It'll be the last part of my project to hit fruition.
The multiconnector wires are new to me and look promising. Additionally, I kept thinking, and came up with DB25 (parallel, basically old printer cables) which seem like they might work very well, and there's breakout boards already on ebay for like $3.00 each. I'll likely run DB25 to each "set", and then a cat5 to each singleton (I want to keep components hot-swappable as much as possible, so if for example an led burns out during a tournament, it can be easily remedied).
I need millisecond timing, and consistent, so I'm using a Chronodot temperature-compensated RTC.
As each lane has a minimum of 4A and 66digital inputs to be read, plus outputs for all of the 66 leds (although I can power them in series in some fashion), plus the RTC and communication with the other units etc, I decided I needed a centipede, or mess around with port expanders omore directly.
It's a fairly involved project
