Adding Another Optical Sensor to Garage Door Opener


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Old 02-07-11, 03:29 PM
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Adding Another Optical Sensor to Garage Door Opener

We have a Craftsman Electric garage door opener with an optical sensor set mounted about 6" above the garage floor. We just got a new vehicle that has a rear lift gate. When it is open, it touches the open position garage door. I put some rubber bumpers on the door to protect the open liftgate. If someone would try to close the overhead door while the liftgate is in the open position...disaster! I have an extra set of optical sensors, receiver and transmitter. I want to position them such that if the vehicle liftgate is open, the door will be inhibited from closing. Does someone know how I can wire them into the opener? Is it as simple as wiring them in parallel with the existing sensors?
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Last edited by n1ml; 02-07-11 at 04:41 PM.
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Old 02-08-11, 03:23 AM
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Ive tried it in series and parallel, and could not get it to work
 
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Old 02-08-11, 09:41 AM
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The opener is designed to reverse when it senses an obstruction but it does exert a little pressure before this happens. You can stop the door closing by hand and feel the pressure. It will reverse to the open position. If you don't feel comfortable with this you can raise the existing door sensors. Not recommended if you have small children or pets.
 
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Old 10-28-12, 11:27 AM
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I have the exact same issue as the OP figpickle, except that the disaster actually happened to us, causing a whole ton of scratches right down our minivan's rear lift gate. The pressure settings on the door were already set as low as possible but it didn't help (any lower and the garage door sometimes does not close properly), it just pushed the lift gate shut scratching it, so I started to google how to wire in 2 extra sensors in parallel/series and it led me here, so I'm sad to see that Doorman2722 already tried this and was unable to get it to work.

I'm only resurrecting this thread to see if anyone else has tried it and also failed, since there is a chance that perhaps Doorman2722's attempt wasn't done properly (there's a chance! right?). I really hope there is a way of getting it to work because it would be perfect if it did so that it would sense the liftgate when it was up and not allow the door to close...

I'll keep researching this, and also know someone with some sensors from a garage door opened (same brand, craftsman) that they haven't yet installed in their garage so I'm thinking I may just borrow theirs and give it a try myself...
 
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Old 10-28-12, 12:18 PM
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I've never added a second set of sensors to the door system but I'll give you a hand if you'd like. We'll have to do a little bit of checking with a volt/ohmmeter. Do you have one ? Are you up for a challenge ?

If you have a meter and want to get started.....connect red meter lead to terminal 2 and black meter lead with terminal 3. What voltage do you measure ? Now block the sensor....what do you measure now.
 
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Old 10-28-12, 12:37 PM
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Well...no offense to anyone...but if Doorman tried it and couldn't get it to work...I doubt it will be as simple as wiring changes.

If you open them up and modify the circuitry somehow, I guess it could probably be done. IIRC the boards in them are pretty simple.

A couple of suggestions that may help....

Back in to the garage....there are sensors that can tell you when you are clear of the door and not too far back.

Buy a garage door open/closed sensor like this Shop Chamberlain Garage Door Monitor at Lowes.com but instead of attaching the transmitter to the door, attach it to the liftgate and put the receiver near the garage door opener button. If the red light is blinking DON'T close the door til you close the hatch. It's a simple switch in the transmitter that changes state between vertical and horizontal. Would work easily on a van hatch.

I have one that I made an angled mounting bracket for and attached it to the garage door. Not so I could tell if it was open or closed so much, but so I know if it's open enough for ventilation, but not so much someone can slide under it. If it's open more than 6" or so...it flashes red. I like to leave it open for ventilation on the hot summer nights.
 
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Old 10-28-12, 02:00 PM
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Liftmaster has an interface to make residential photocells work with older commercial operators. I don't know the part #, but it would need a 24v transformer to power it, and has a normally open output that in parallel would short out the photocells when the second photocell is interrupted. This would do the job, or any photocell with a relay output could be used in parallel, or in series with a normally closed output. Normally closed in series would be best, the resistors that feed power to photocells often run hot. Shorting the photocells for extended periods of time in hot weather could damage some operators.
 
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Old 10-28-12, 08:23 PM
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The sensors don't work the way that one would expect. They're an uneven square wave, higher voltage, with weird pattern of low voltages. A change in the pattern causes the opener to reverse.

I had considered adding my own extras but it's certainly something that will require electronics experience to make work, as a controller would be necessary.
 
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Old 10-28-12, 08:38 PM
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Thanks T-W-X....now I'm going to have to go out and buy a set to play with.


I had figured that maybe the units sat on the same line and when beam was interrupted the receiver performed a momentary short.

One approach to this problem would be to mount the transmitter at the 6" point and on the same side of the door mount the receiver at the height needed to protect the hatch. Use two mirrors on the opposite side of the door. Would require some extreme patience to aim correctly.
 
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Old 10-29-12, 02:19 PM
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Well I just had this happen to my vehicle. Not only did it happen once but twice now. The first time I accidently pressed the tailgate open button on my key fob and the tailgate opened and then without knowing it was open my son pressed the garage door open button scrapping the garage along the bottom edge of the door on its way up. The second time my wife had the tailgate open and pressed the wrong button for the door and instead of opening the other door she closed the one with the tailgate in its way. What a mess of the tailgate on my new Benz.

Now the first problem I can rectify by mounting the sensors on an angle so that instead of the lower sensors being 6" of the floor the one sensor is mounted 48" of the floor and the whole thing on an angle. That way the bumper and the tailgate will be in the path of the sensors.

The last problem is not so easy. The sensors when aligned feed a square wave pulse every 6.5 ms into the opener. The voltage is also not standard so there is no way really to mess with it. But you can break this signal source and the door will reverse. So my thought is to add a bar to the inside of the garage door that normally would hang lower than the door when it is open (gravity) so if the bar comes in contact with an object the bar would lift up breaking a sensor which in turn would break the signal back to the opener causing it to reverse. Now of course what to do when the bar hits the garage floor. Now you need another sensor and a means to detect the last 4" that would not allow the sensor on the bar to break the signal back. So now I will need to purchase some sensors and a couple of the relays and rig the whole thing up.
 
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Old 10-29-12, 09:57 PM
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The last problem is not so easy. The sensors when aligned feed a square wave pulse every 6.5 ms into the opener.
I'm curious.....how did you find this out ? Did you actually see it on a scope ? I'm working on a dual sensor solution. Actually based on what you've said it might be easier to install a generic photo eye system and set it up to open the line coming from the factory sensor system thus removing the 6.5ms signal from the opener.
 
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Old 10-30-12, 08:22 AM
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There was actually a you tube video posted on this, where someone took a scope and showed the results. I replaced a garage door opener a few years ago and all I did was to replace the main unit with the one (different brand) and hooked the old sensors in and everything worked, so I figured they cannot be brand dependent.
Bypass garage door safety sensor.wmv - YouTube
 
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Old 11-01-12, 04:08 AM
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I replaced a garage door opener a few years ago and all I did was to replace the main unit with the one (different brand) and hooked the old sensors in and everything worked, so I figured they cannot be brand dependent.
Chamberlain makes operators under about 20 different names, Genie has a few also. You probably bought the same thing with a different name.
 
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Old 11-03-12, 03:41 PM
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@ PJMax

I was actually planning on doing that. It'll be at least a few more weeks till I can get my hands on an extra set of sensors... but eventually I'll get the 'ol voltmeter out and start messing around with the extra 2 sensors in parallel/series with the existing 2 sensors... I'm sure it won't work but it might make for a fun few hours of screwing around...
 
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Old 11-04-12, 10:31 PM
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Try to get your hands on a genric photo beam system. Many around at surplus sites. That would definitely work for a second sensor system. Most of the genrics have a form C relay which is ideal for this application.
 
 

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