Yes, the garage door safety beams are powered from the same source and the power going to them is modulated at a given frequency. Interrupt the beam and you interrupt the circuit looking for that frequency. Many people have tried to use safety beams only to learn that a lot more is going on than just a beam.

I'm down with the beam breaker sensor setup. An IR LED and an IR photo transistor mounted in tubes with nail hole (not pin hole) openings and properly aligned can sense when someone has tripped the beam. With the 555 acting as a one-shot, once triggered by a hand, foot or torso - the 555 can hold the signal for 2 seconds and the count will advance one step.

Using a binary counter chip coupled with a 7 segment decoder driver (been a long time since I messed with these things) and you have your counter. As long as the runner doesn't complete a lap in under 2 seconds (absurd of course) you get an accurate count.

I, too, am wondering about the number of runners. Are there multiple runners on the track at the same time? Or are we counting a single runner?

 

Multiple runners would require multiple gates, OR each team would have a flag to slap as the runner went by. That would be cheaper to implement. And using a laptop to do the counting would be cheaper than building a counter and display. It might be a challenge to keep an older laptop running for a few hours, I think that the event was to run quite a while.
A ten bit binary counter could display up to 512, and that might be an entertaining display to have. Certainy simpler than 3 large digits.

 

Hello there .A belated welcome to AAC!
Just disregard the technology not needed for your specific application, if nothing more it will just give you more ideas options.
I hope this helps.
Electronic track baton device.
https://patents.google.com/patent/US9126094B1/en

 

Those garage door systems are quite interesting and not at all like a simple photoelectric sensor system.

Yeah but all you need is the sensors. The basics cost about $30 on Amazon.

Ron