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

["Bob F" <bobnospam@xxxxxxxxx>]

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.