If you’re on a bicycle approaching 5th and 2nd (Central High School) from the west, the light will trip if you spend that last block in the exact middle of the left-turn lane (the one nearest the yellow line). I don’t know if there is a camera sensor or one in the ground, but this seems to be working for me. I generally stop in the crosswalk so people in cars can pull up to the stop line and trip things if I haven’t managed to.
Oh, and it’s not just Grand Forks that has this problem.