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

[G. Morgan <G_Morgan@xxxxxxxx>]

Art Todesco wrote:

>On 7/4/2012 9:48 AM, G. Morgan wrote:
>> 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.
>>
>It may be current change, but if you look way earlier in the thread, I
>put a scope across the pair.  There are pulses there, but when the beam
>is broken, they disappear.

Did you try measuring current in both states?