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

[Art Todesco <actodesco@xxxxxxxxx>]

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.