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

["Bob F" <bobnospam@xxxxxxxxx>]

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.