[Mr Muntarg]

Hi, will follow with interest.

Just a thought, the Arduino Uno only runs at 5v if powered over USB.  If you use the AC in you can power it using anything from 7-12v.  So if running your lanes at 12v you can power the UNO too using the single supply and needing no step down regulators.

I am rebuilding my track now, but had it setup for Race Coordinator too using a single power supply,  But in my case I powered the Arduino direct over USB from the PC as they sat next to each other anyways.

Ohh I wasn't aware or had forgotten at least that the UNO could run 12v . I've ordered a 15v DC supply so may not suit anyway . I was under the impression from a post on slot forum that usb power wasnt enough. But i guess its must be. I may just run it off that for now then. 

What are you using for lap sensor. I've ordered these https://www.ebay.co.uk/itm/115909533176. Don't really have any experience with photo sensors , but i figured can't be too far out and cheap enough