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

["Bob F" <bobnospam@xxxxxxxxx>]

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?