I home-brewed a whole system years ago when they were still bulbs instead of LED's.
I'm assuming you have the newer and smaller LED units. One of the things you have to be aware of is that LED's are not created equal for flasher systems - you can end up with either a common anode or common cathode system. The NJI's only work with selected units. I found that out the hard way - I toasted my previous flasher unit. I 'think' the flasher unit I have now is a Dalee 367.
https://www.dallee.com/PDFs/Appl;ication%20Notes/367_Flasher_applications.pdf Frankly I liked the old Walthers better as it had a slower flash rate, but the new one is OK if you slow it down as much as possible.
I powered the gates with two Tortoise switch machines mounted sideways on homemade brackets. Because they can stand being left powered-on, I just control them with a simple DPDT reversing switch. I bent the steel wire to an 'L' and put a small brass alligator clip on it so that it was easy to adjust the position on the .010 brass wire I use as a pushrod to the gates themselves.
The way a Tortoise is built you can adjust the throw distance and throw range very easily just with the plastic slider on top. Like I said, other than the use of a micro alligator clip on the end of the throw wire so that you could easily adjust the up and down stop point on the gates I don't think I invented anything particularly different here. More photos if you really want them, but it's very location specific. I had to drop down through two levels of benchwork before I had enough room to mount everything.
I put a Radio Shack rocker switch so that as soon as the gate mechanism starts to move down, the lights flash; a second one triggers the sound track which is a Radio Shack digital recorder. I put the motor controls for the tortoise on a terminal block so I could experiment with various resistors to slow the gate speed down, not sure what I ended up with but it worked rather well.
The whole system has worked very reliably for about 15 years. "before" I changed it over to LED gates, it looked like this:
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As far as for detection, I have bidirectional main lines with a crossover in the middle, a passing siding and an industrial spur (4 tracks) at this crossing. Designing that was more of a headache than it's worth - a DPDT switch works just fine, thank you.
