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

["Bob F" <bobnospam@xxxxxxxxx>]

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.