I want a beam detector across the inside of my garage door that is blocked when a vehicle is too close to the garage door. An audible alarm will sound when the beam is interrupted; thus, as long as the rear of the vehicle is too close to the garage door, the warning indicator will sound. I would like to keep all the electronics co-located in order to simplify power and other connections.

I think I can handle the control functions, but I am not sure about the beam. Would a laser be a better choice than a IR beam, since I will probably use a mirror? And how hard would a laser and mirror be to align? Someone with some real world experience...please give me advice.

Thanks.

 

I think a ultrasonic range finder thing mounded on the garage door itself is the best option, rather having to align lasers/ir transmitters and receivers.

 

How about a simple tyre operated microswitch positioned at the rear of the garage that tells you when you're far enough in?

 

I have three different vehicles that may be parked in the garage; they are all different lengths. I need a beam to accommodate the overall length differences and the differences from the rear wheels to the back of the car.

 

Put three marks on the garage floor and make the switch mechanism portable?

 

I have one of those ultrasonic stop lights. It works great to show you are nearing the front of the garage (opposite the door), or at least the sensor.

To indicate when you are at the minimum distance in from the door using a laser, I think you'd need to sweep a plane, a rectangle from ~1' to ~3' off the floor and as wide as the door, to be sure every part of the bumper had cleared the plane where the door might touch it as it closes.

 

I use a high-tech tennis ball on a string hung from the ceiling. The height is set to just touch the windshield when I've pulled in far enough.

As a side benefit, my 6 y.o. likes to bat the ball when the car is not there.

I suppose electronics could work as well...

 

Buy a tennis ball and get some string. Also a nail. Required tools: hammer and something to cut string. A ladder may also be helpful.

Park car *correctly* in the garage. Punch hole in ball and insert one end of the string.

Tie the string to the ceiling so it just touches the center of the windshield. Then toss out any ideas about complicated electronics that needs alignment.

Now you can safely just drive your car into the garage till you once again make contact with the tennis ball and know all is well.

 

Read post #4. A front mounted solution won't work for different length vehicles.

Perhaps you could use an IR beam break system such as this. Note that it uses a corner reflector type reflector (similar to an automobile reflector) so the alignment is not so critical.

 

Thanks for the suggestions, but I want to use a beam. I can place the beam at bumper height, which is approximately the same on all three vehicles, and avoid the need for scanning. I have heard that IR beams used with reflectors can be fooled by the reflection from a vehicle. What I would like is someone who has done a similar project to advise me of the relative advantages and disadvantages of lasers versus IR beams.

Thanks.

 

You are right that a reflective device might not be a good idea, because the side of the car might also reflect the light, but if you can deal with electronics on both sides of the garage, I think either IR or a laser would work. Maybe the laser could be out of one of those cheap pointer units, if you could replace the battery with wires coming from a power supply.

If you go with the laser though, you'll have to install it so it points at the receiver exactly, and you can't let either unit shift. With an IR system, the alignment isn't critical. An LED and TV remote receiver component ought to do the job.

 

Do you have the IR pair that's installed with new doors to reverse it if beam is broken? If so, I would simply relocate the transmitter/receiver pair to bumper height. They are typically mounted about 6" off the floor, which I think is a little low, but they didn't ask for my opinion....

 

Do you have the IR pair that's installed with new doors to reverse it if beam is broken? If so, I would simply relocate the transmitter/receiver pair to bumper height. They are typically mounted about 6" off the floor, which I think is a little low, but they didn't ask for my opinion....

That's an idea, but I wonder about my cat getting squashed. I wonder if it's possible to put another set of sensors in parallel with the ones that are there.

 

I think that should definitely be possible. In fact I think I've seen garage doors with both a cat-height sensor as well as a child-height one.

Trouble is, not all numbers are the same height? Maybe there's an overlap.

One stupid question: Why don't you just pull in as far as you can, or to a set stop line, like everyone else?

Oh, and about the cat. I watched the other day, with my hand on the button, as my door came down to where my cat was sitting directly under it. The stupid thing didn't move until it was pushed out of the way (and when I panicked and pushed the button). I'm sure it had no idea how close to death it was. The sensor is a good idea.

 

That's an idea, but I wonder about my cat getting squashed. I wonder if it's possible to put another set of sensors in parallel with the ones that are there.

I think that is possible...Not a cat person, we have dogs, but I would think a cat would run when the door moves..

 

According to some internet postings, it is not possible to simply put another pair of sensors in parallel with the first. Apparently, the transmitter sends a square wave signal to the receiver, which tells the controller that there is no blockage. My assumption is that if I had two sets in parallel, it would essentially be an OR gate, and unless both sensors were blocked, the garage door would close. I need to think about this some more.

The reason I want this is that three different length vehicles may be parked in the garage, and whichever vehicle is there, I want to pull in only as far as necessary to let the door close, thereby leaving as much clear space as possible in front of the vehicle.

 

...thereby leaving as much clear space as possible in front of the vehicle.

That's what I figured.
One thing to contemplate is having something mounted on the car that interacts with something mounted in the garage. A small reflective sticker in the right spot might work, for instance, without marring the appearance. Or a laser beam pointing down that is only on when the brakes are pressed. Just thinking out loud.

 

You could use a photo sensor with dry contacts wired in series with the down button

 

Oh, and about the cat. I watched the other day, with my hand on the button, as my door came down to where my cat was sitting directly under it. The stupid thing didn't move until it was pushed out of the way (and when I panicked and pushed the button). I'm sure it had no idea how close to death it was. The sensor is a good idea.

My cat likes to jump up on the vehicle, then jump up to the garage door (while it's in the open position), and take a nap. Once, I got in the truck, backed out, closed the garage door, and dumped him out the front of the garage. Apparently, there was just enough room between the panels and the header for a cat to pass. You would think he would have learned his lesson, but not so.

 

You could use a photo sensor with dry contacts wired in series with the down button

Maybe I'll try moving the receiver to bumper height, leave the transmitter at six inches, and add a couple of mirrors. That will convert the challenge from electrical to mechanical.