Yesterday I replace my 30 year old Sears Craftsman garage door opener with a new Craftsman one. Id maintained the old one over the years, but it had become annoyingly intermittent with the door stopping or reversing at various spots during its opening and closing and I couldn't easily locate the source of the problem.
Thirty years ago photoelectric safety beams for garage door openers either didn't exist or weren't very common. Now they are standard equipment for home garage door openers.
I installed and connected the photoelectric source and receiver modules six inches off the floor on both sides of the door opening yesterday. I was sort of surprised the see that each module had a two pair conductor lead and there were just two connection points on the opener mechanism to attach those leads in parallel. I would have expected at least three connection points, a common and one for each of the two modules.
So, my curious mind is trying to figure out why there are only two connection points, without having to drag a bunch of test equipment into the garage or trying to obtain a schematic of the opener's circuit board.
My best guess is that when the photocell sees the light from the source it switches in a load which significantly increases the total current drawn from the two modules, sensed by a level detector in the opener's electronics. When the beam gets blocked the current drops below the level detector's threshold which tells the opener there is something in the door's path.
Am I maybe correct?
Jeff