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

[Art Todesco <actodesco@xxxxxxxxx>]

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.