Anyone know effective ways to find studs/joists on popcorn ceilings?

Covering popcorn ceiling with drywall. Saw a youtube video and some guy used his studfinder over piece of cardboard, put it up to popcorn ceiling and he claimed it worked. I tried to no avail. On the 2nd floor it was easy to find the studs in the ceiling because we just went up to the attic and could tell where... show more Covering popcorn ceiling with drywall. Saw a youtube video and some guy used his studfinder over piece of cardboard, put it up to popcorn ceiling and he claimed it worked. I tried to no avail. On the 2nd floor it was easy to find the studs in the ceiling because we just went up to the attic and could tell where they lied 16 inches apart. But on the main floor/living room, where we plan on doing the next project, I am having a difficult time trying to find the studs in the ceiling. Anyone have any tips?

Thanks
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