Garage Door Opener - Electric Eye

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Have a neighbor w/ garage door troubles.
Can someone explain (from a voltmeter's perspective) how these things
work?

I can get it to work right if I aim the electric eye sensors directly
into each other and tape them up, but if I try to actually aim them
across the opening, the door will not close.  (It may not open either,
but I never tested that..)

With both eyes disconnected, the terminals on the back of the main
unit read about 12 volts.  With one eye connected, that drops to about
7.8 volts, and with both sensors, it drops to about 7.3 volts or so.
However, I can't really see much meter deflection whether the eyes are
aimed or not, even when they are taped together.

However, when taped directly together (so that one sees directly into
the other and there is no possible chance for misalignment!!), the
door does indeed work correctly.

I'm assuming these electric eyes are current mode??
That might at least explain the lack of a discernable voltage when
aligned, not-aligned...?

There are no polarity markings on the electric eyes, and opening up
both showed a full-wave bridge (4 diodes anyway that look suspiciously
like a bridge!), so I'm assuming polarity does not matter. (?)
Either way, the voltage magnitudes did not change much when trying the
wires reversed.

Any ideas what could be going on here?
Can this really be just an alignment problem, or to you think the eyes
are defective?
They are newly replaced (before I got involved).  I have no idea where
the orignal ones went off to.

Thanks in advance!!
-mpm

It's a Sears unit, "Genie", I think?
Pretty hefty size door.  2-car with hurricane braces.   Probably a 3/4
horse.

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Oh, I should also have added...
Each electric eye has an LED.

I suspect one is a transmitter and the other is a receiver. (?)

Anyway, the one with the GREEN LED is on all the time.
The other one (receiver?) has a RED LED which toggles on or off
depending on whether the beam is obstructed.
RED 3D% Clear,  RED off 3D% obstructed.

Please note that the LED's behave this way when (I'm pretty damn
certain) they are aimed correctly, yet the door will not close.
(It also might not open, but I didn't test that).  And as I mentioned
previously, the DC voltage doesn't seem to change much, if at all
regardless of what the LED's are doing.

-mpm

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Start here:
http://www.geniecompany.com/GenieCompany.aspx?cid32%2

--Winston

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The signal could be pulsed (modulated), and you won't see them with a
DC meter.

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Good point.  I honestly didn't think of that.
I just assumed something as "industrial" as a garage door opening
would be "simple".

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mpm wrote:
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   No, they are usually modulated to prevent problems from other light
sources.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

Re: Garage Door Opener - Electric Eye



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In today's world, nothing is simple!

A common scheme is to pulse the led, and measure the drop on the
receiver's power suppply. This is done by wiring both to the same
(current limited) power source, sending a pulse and looking at the
current drawn. Too little current, and the system knows the sensor eye
is blocked, enough current and it knows the sensor is seeing the pulse
from the LED. Pulsing is used to both allow comphensation for ambient
light, and to provide a basic reference point for the blocked sensor
mode (OK, these are basically the same thing...)

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That's exactly how this one's wired.
So, I guess it really is an alignment issue....  Sure didn't look like
it though.
Maybe I can tie a string (tight) across the door opening and aim them
that way???

This sounds like a pain in the ass...

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(...)

Did operation improve after you cleaned the lenses?

--Winston

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Try a laser pointer or one of those levels with a laser.

The opener I have the receiver LED turns on when they are aligned.

--
Joe Chisolm
Marble Falls, Tx.

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