As promised - electronics and code are working well!
Unfortunately the camera module for my Raspberry Pi broke when I tried to put it in an ill-fitting case, so I'm waiting for a new one to come in before I do development on the instant replay. In the meantime, I'm working on putting all of this in a nice looking box to attach to the finish gate.
I'm trying to decide for the start gate if I want to use an RCA plug and speaker wire, or if I want to use phone wire with an RJ11 phone jack. Not sure it matters, if anyone has an opinion.
More to come...