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

["Bob F" <bobnospam@xxxxxxxxx>]

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?