Hey guys I’ve been working on a how-to for making an electronic finish line for a while. I finally finished it. There is an extensive post with pictures and links you can find here: www.racehotwheels.com/2020/01/diy-hot-wheels-finish-gate-build-your.html
It is based on the finish line that I use on my shelf track. I wrote it so that if you have zero electronics background you should still be able to build it. I also wrote it so that if you have limited resources and building skills, you should still be able to build it. If your skills or resources are more advanced, take the basic idea and get creative. I also made a video. The post is way more detailed, but here is the main idea.
Hopefully this will be helpful for some of you. Let me know if anything is unclear in the article so I can fix it and make it more understandable.