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



On 7/4/2012 11:53 PM, G. Morgan wrote:
> Bob F wrote:
>
>> G. Morgan wrote:
>>> Art Todesco wrote:
>>>
>>>> On 7/4/2012 9:48 AM, G. Morgan wrote:
>>>>> Art Todesco wrote:
>>>>>
>>>>>> On 7/3/2012 7:42 AM, Art Todesco wrote:
>>>>>>> On 7/2/2012 2:12 PM, Bob F wrote:
>>>>>>>> Art Todesco wrote:
>>>>>>>>> On 7/1/2012 10:55 PM, Bob F wrote:
>>>>>>>>>> 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?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> I'm not sure where the pulses are coming from.  In my case, the
>>>>>>>>> source and receiver both have 2 wires and are actually
>>>>>>>>> connected together in parallel and then go to the main opener
>>>>>>>>> unit on the ceiling.  I'm sure the 6 volts come from the opener
>>>>>>>>> unit, however, I really don't know where the pulses come from.
>>>>>>>>> I just monitored, using an oscilloscope, between the 2 wires.
>>>>>>>>> I'm guessing that maybe the pulses are put on the 6 volt power
>>>>>>>>> in the opener unit and when the photo receiver is blocked from
>>>>>>>>> the LED light, it somehow shorts out the pulses.  And when the
>>>>>>>>> opener see that the pulses disappear, it reverses the door.
>>>>>>>>> But, the
>>>>>>>>> pulses could be coming from the receiver box.  Without a
>>>>>>>>> schematic, I'm running blind.  I think I will try calling the
>>>>>>>>> door installer to see if he has some info.
>>>>>>>>
>>>>>>>> Wow! I never would have thought they would be in parallel. Gotta
>>>>>>>> think about
>>>>>>>> that.
>>>>>>>>
>>>>>>>>
>>>>>>> Yeah, me neither.  I called the garage door installer that put in
>>>>>>> the openers and doors, and he was totally clueless.  Didn't know
>>>>>>> anything of a schematic.  My guess is that the pulses come from
>>>>>>> the logic board in the opener unit and the photo receive filters
>>>>>>> them out to power up the receiver.  Then when the beam is
>>>>>>> interrupted, the receiver puts clean 6 volts on the wire pair,
>>>>>>> thus 'shorting' out the pulses.  The logic board then detects
>>>>>>>     this and reverses the door.  But, as I said, just guesses. Of
>>>>>>> course, if you are operating the units on a fixed 6 volt supply,
>>>>>>> not from a LM opener, I don't think you'd see the pulses ...
>>>>>>> again, just guessing.  Do you see the green LED flickering on
>>>>>>> your units?  If you hold the 2 units together so that the
>>>>>>> receiver always sees the light source, then move the 2 back and
>>>>>>> forth rapidly, you should be able to see the green LED blinking
>>>>>>> (strobe effect).  My guess is you won't unless it is connected to
>>>>>>> a LM opener.
>>>>>>>
>>>>>> I called Chamberlain/LiftMaster today and asked about a schematic.
>>>>>> I'm not sure the person even knew what a schematic was.  It wasn't
>>>>>> on her script ... and she was in the US!   She finally gave me
>>>>>> another phone number, which I called and the person said they
>>>>>> didn't have them.  I sarcastically asked if they get built by
>>>>>> magic.  She then said the schematic was proprietary.  Most
>>>>>> companies are usually good about giving out schematics.  I thanked
>>>>>> her and said that if I reverse engineered a schematic from the
>>>>>> unit,  I would be sure to post it on the internet!  I have a
>>>>>> Garage Butler to auto close the door if left open, and I found a
>>>>>> schematic on the internet, but couldn't find anything on the LM
>>>>>> photo sensors.   I really don't want to take apart my working
>>>>>> units.  I know the LM opener will not work if the photo sensors
>>>>>> are not connected and working properly.  So, if I find some cheap
>>>>>> ones, I will work on it.
>>>>>>
>>>>>
>>>>> I'm not exactly sure, but I think they operate on current.  A
>>>>> resistor in both sensors in parallel, one drops out and the
>>>>> current changes, but not the voltage.
>>>>>
>>>> It may be current change, but if you look way earlier in the thread,
>>>> I put a scope across the pair.  There are pulses there, but when the
>>>> beam is broken, they disappear.
>>>
>>> Did you try measuring current in both states?
>>
>> Or, does the LED driving voltage from the opener change, and how, if you
>> disconnect the send from the circuit?
>
>
> When the beam breaks, only one LED goes out on the receiver - correct?
> Maybe the absence of the load changes the "safe state".  I think the
> transmitter has the circuit set at a semi-precise current flow. If it
> always has 6 volts and internal resistance/load that also stays constant
> in a "safe state" - the logic board at the operator can always be
> looking for a current range.  6V/50 ohms = 120ma, I'm proposing the
> logic board is expecting to see 120ma +/- 10% (in this example) and a
> break in a wire or beam will do the trick.
>
I didn't actually measure current.  I wanted to disconnect the 2 wires
from the opener to see what the opener is putting out.  From what I've
read, if you don't have the photo sensors connected, the opener won't
work properly.  Maybe that means it won't close, but I've not tested it.
  But I think the detection of a broken beam really has something to do
with the pulses.  As I said previously, the pulses are on the pair when
the beam is uninterrupted.  Once the beam is broken, the pulses
disappear.  The pulses repeat every 6.5ms and basically shut off the 6
volts for a very short 0.3ms.  These can easily be filtered out in the
receiver with a simple RC circuit to power the receiver.  My thought is
that the pulses come from the opener, but I haven't check that either as
of yet.



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