Re: How to use Liftmaster garage door IR safety sensors for other uses?

[G. Morgan <sealteam6@xxxxxxxxxxxxxxxxx>]

Art Todesco wrote:

>On 7/3/2012 7:42 AM, Art Todesco wrote:
>> On 7/2/2012 2:12 PM, Bob F wrote:
>>> Art Todesco wrote:
>>>> On 7/1/2012 10:55 PM, Bob F wrote:
>>>>> Art Todesco wrote:
>>>>>> On 7/1/2012 3:04 PM, Bob F wrote:
>>>>>>> Art Todesco wrote:
>>>>>>>> On 6/29/2012 7:17 PM, Bob F wrote:
>>>>>>>>> Bob F wrote:
>>>>>>>>>> Art Todesco wrote:
>>>>>>>>>>> On 6/25/2012 5:37 PM, Bob F wrote:
>>>>>>>>>>>> I picked up a couple pairs of these Liftmaster 41A5034 garage
>>>>>>>>>>>> door safety sensors, which I thought I might be able to use
>>>>>>>>>>>> for other sensing on my homebrew home control system. Does
>>>>>>>>>>>> anyone know what voltage/current the sender needs, and what
>>>>>>>>>>>> connections the 2 wire detector needs and how it signals. They
>>>>>>>>>>>> both have white 2 conductor wire with a black line on one of
>>>>>>>>>>>> the conductors.
>>>>>>>>>>> I have them on my 2 garage doors.  I installed an addition unit
>>>>>>>>>>> called Garage Door Butler, which automatically closes the door
>>>>>>>>>>> if accidentally left open.  What I'd like to do, is to use the
>>>>>>>>>>> info from the safety sensors to reset the Butler unit so that
>>>>>>>>>>> each
>>>>>>>>>>> time you break  the beam, the Butler would reset back to the 10
>>>>>>>>>>>      minutes I have it programmed for. But, I too, don't know
>>>>>>>>>>> how they work. I would like to have a small relay operate
>>>>>>>>>>> whenever
>>>>>>>>>>> the beam is broken.  The contact on the relay could easily
>>>>>>>>>>> reset the Butler.
>>>>>>>>>>> The one odd thing I've noticed is that both the light source
>>>>>>>>>>> (IR) and receiver box have 2 wires each.  They connect in
>>>>>>>>>>> parallel
>>>>>>>>>>> and then go to the opener unit as just 2 wires. I've want to
>>>>>>>>>>> put a voltmeter/oscilloscope across the wires and see what it
>>>>>>>>>>> looks like, but just haven't had the time.  I've also wanted
>>>>>>>>>>> to call
>>>>>>>>>>> the guy that installed the doors (new house 3 years old) and
>>>>>>>>>>> see if he has a schematic, but I haven't done that yet.  I'll
>>>>>>>>>>> keep an
>>>>>>>>>>> eye here and also will let you know if I find out something.
>>>>>>>>>>
>>>>>>>>>> My best guess so far is that the "receiver" conducts more
>>>>>>>>>> current when the IR is ON (or maybe off) and not the other way,
>>>>>>>>>> so that the voltage at the end of the wire provided through a
>>>>>>>>>> resister will drop as the current increases.
>>>>>>>>>
>>>>>>>>> The above is pretty much the case. With 1k resister on either end
>>>>>>>>> going to the "black/white" wire from the (+) terminal of a 9V
>>>>>>>>> battery, white wire to (-) terminal, it senses properly. Feeding
>>>>>>>>> the receiver end signal (green LED) into the opto-islator LED
>>>>>>>>> input of my home control should work fine.
>>>>>>>> I went out in the 92 degree heat today to put out the flag and I
>>>>>>>> decided to checked my garage door photo sensors.  When the beam is
>>>>>>>> interrupted, the voltage across the 2 wires read 6 volts DC.  When
>>>>>>>> NOT interrupted, is read 5.75 volts DC.  I thought there might be
>>>>>>>> more to it than DC volts, so I got out the scope.  The 6 volts is
>>>>>>>> actually interrupted periodically.  It shuts off for about .3ms
>>>>>>>> every 6.5ms.  When the beam is interrupted, it is a steady 6
>>>>>>>> volts DC. Using an opto to the LED is probably the easiest way to
>>>>>>>> get info.  I didn't look directly across the green LED, but I
>>>>>>>> think it is probably interrupted with the power because, if you
>>>>>>>> turn your
>>>>>>>> head
>>>>>>>> very quickly, it is definitely blinking.
>>>>>>>
>>>>>>> I wonder if they cycle it to detect other IR sources that could be
>>>>>>> jamming the sensor?
>>>>>>>
>>>>>>>
>>>>>> Actually, I think they just use it to know if the beam is
>>>>>> interrupted or not, plus you can send power to both the light
>>>>>> source and the
>>>>>>    receiver. As I didn't take anything apart, I don't know how the
>>>>>> receiver can stop the pulses across the power pair when the beam is
>>>>>> broken. It
>>>>>> would be nice to have a schematic.
>>>>>
>>>>> Clarify for me - Is the power to the receiver pulsed also?
>>>>>
>>>>>
>>>> I'm not sure where the pulses are coming from.  In my case, the source
>>>> and receiver both have 2 wires and are actually connected together in
>>>> parallel and then go to the main opener unit on the ceiling.  I'm sure
>>>> the 6 volts come from the opener unit, however, I really don't know
>>>> where the pulses come from.  I just monitored, using an oscilloscope,
>>>> between the 2 wires.  I'm guessing that maybe the pulses are put on
>>>> the 6 volt power in the opener unit and when the photo receiver is
>>>> blocked from the LED light, it somehow shorts out the pulses.  And
>>>> when the opener see that the pulses disappear, it reverses the door.
>>>> But, the
>>>> pulses could be coming from the receiver box.  Without a
>>>> schematic, I'm running blind.  I think I will try calling the door
>>>> installer to see if he has some info.
>>>
>>> Wow! I never would have thought they would be in parallel. Gotta think
>>> about
>>> that.
>>>
>>>
>> Yeah, me neither.  I called the garage door installer that put in the
>> openers and doors, and he was totally clueless.  Didn't know anything of
>> a schematic.  My guess is that the pulses come from the logic board in
>> the opener unit and the photo receive filters them out to power up the
>> receiver.  Then when the beam is interrupted, the receiver puts clean 6
>> volts on the wire pair, thus 'shorting' out the pulses.  The logic board
>> then detects this and reverses the door.  But, as I said, just guesses.
>>   Of course, if you are operating the units on a fixed 6 volt supply,
>> not from a LM opener, I don't think you'd see the pulses ... again, just
>> guessing.  Do you see the green LED flickering on your units?  If you
>> hold the 2 units together so that the receiver always sees the light
>> source, then move the 2 back and forth rapidly, you should be able to
>> see the green LED blinking (strobe effect).  My guess is you won't
>> unless it is connected to a LM opener.
>>
>I called Chamberlain/LiftMaster today and asked about a schematic.  I'm
>not sure the person even knew what a schematic was.  It wasn't on her
>script ... and she was in the US!   She finally gave me another phone
>number, which I called and the person said they didn't have them.  I
>sarcastically asked if they get built by magic.  She then said the
>schematic was proprietary.  Most companies are usually good about giving
>out schematics.  I thanked her and said that if I reverse engineered a
>schematic from the unit,  I would be sure to post it on the internet!  I
>have a Garage Butler to auto close the door if left open, and I found a
>schematic on the internet, but couldn't find anything on the LM photo
>sensors.   I really don't want to take apart my working units.  I know
>the LM opener will not work if the photo sensors are not connected and
>working properly.  So, if I find some cheap ones, I will work on it.
>

I'm not exactly sure, but I think they operate on current.  A
resistor in both sensors in parallel, one drops out and the
current changes, but not the voltage.