On 2/6/2016 1:41 PM, Ralph Mowery wrote:
"Don Y" wrote in message
...
IME, the photocells aren't worth their cost. They really only detect
things
that are ON the garage floor IN the path of the beam.

E.g., a kids wagon or bicycle typically won't trip the detector (the light
shines under or through). The same is true of vehicles (unless their
front
or rear axles are in the path.

I mounted my photocells about 2 feet off the floor. That way if I don't get
the truck all the way in it may see it.

That's an idea! (D'oh!) Of course, it opens up a "vulnerability" *below*.
But, I suspect there is some "better height" than the 6" that I opted for
initially.

The garage is only about 2 feet
longer than the truck and I have to pull almost top the wall if I want to
get the door shut and maybe walk around the truck with the garage door
closed.

In our case, we have something like 10"!

There are stiffener ribs on the inside of the garage door that eat up ~3 inches
inside the plane of the garage door.

We back in (SWMBO doesn't like backing OUT, into "traffic") so need to
allow space behind the car for the liftgate (otherwise, we'd have to
load/unload the vehicle in the driveway!). This requires 13" for the
liftgate (which swings BACK as it lifts UP).

We try to allow a couple (literally "2 or 3") of extra inches behind the car
so we can STAND there (liftgate open) to load/unload (then, step aside
as the liftgate opens/closes).

I usually have a push broom hanging on a peg board and drive the truck so I
just bump it to let me know when I am far enough in.

I mounted a tennis ball on a string hanging so that it hits the
driver's side mirror as you back in. There's also a dotted line
on the backup camera display that we can use to gauge how close
we are to the objects behind the vehicle while backing in. The
two "indicators" (camera and ball) have to be in agreement before
I'll let the door close! (i.e., what happens if the camera is
ever knocked out of alignment?? : )

A neighbor has a "mat" of sorts that he drives over as he enters
his garage. The mat has a "lip" (like a parking curb) on it that
impedes the motion of the car past the "sweet spot". A nice idea
but I don't know what keeps it from MOVING (or BEING moved!)
when the vehicle's weight isn't holding it in place!