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

[Art Todesco <actodesco@xxxxxxxxx>]

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.