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Thread: Reed Switches & PIRs

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  1. #1
    Automated Home Legend chris_j_hunter's Avatar
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    Default Reed Switches & PIRs

    after doing some experimental plaster trials yesterday (hard-work) 'was thinking about how to run the cable for the sensor-switches for our various doors (single & twin-door french-windows) and door-less door-ways (as it were) ... fitting reed-switches for the doors was what I'd intended, linked-back to digital inputs of convenient modules, but got to thinking about putting a PIR sensor immediately above the doorway, perhaps with a short tube over the sensor, to limit its field of view, instead-of or as-well, to better sense comings & goings ... hmmm, would it work (with Cortex) ?

    not sure about reed-switches ... they say nothing about how far open a door is, or what it's doing, whether it's closed-fast & locked, or not ...
    Last edited by chris_j_hunter; 22nd March 2008 at 01:07 AM. Reason: corrections

  2. #2
    Automated Home Legend Karam's Avatar
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    Limited field of view PIRs above doorways sounds like a good idea though these will probably have to be augmented by another/others in the same room to catch movements elsewhere. One common issue is a PIR in one room seeing movement in another which can cause errors in occupancy assessment.

    Door sensors (eg. reed switches) highly recommended for house entry/exit doors in order to allow more accurate assessment of house occupancy and also for alarm arming function. For traditional hinge doors magnets and reeds can be placed at the top of the door frame rather than side so you could potential choose to have a door deemed closed even when slightly ajar (we've seen some cases where people wanted this). Internal door sensing can be useful if you're the type of person who regularly closes doors, or you may choose just to sensorise doors that will be shut as part of your security plan

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    Automated Home Legend Paul_B's Avatar
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    I have a couple of PIR above doors and they work fine. Although as Karam says positioning is important to ensure they can't "see" into another room. In some cases I would say to get hung about the ideal PIR position as it will always be a compromise. Instead just buy a second PIR.

    I also have a reed switches on my doors and the beauty is they are fast acting so when you open a door they light is already one rather having to wait for a PIR to detect you in the room. One thing I didn't know is that Cortex ignores movement from PIRs when a door is shut. This wasn't configurable before v23 and had a delay of 5 seconds (this is still the default). If I had known this before (i.e. RTFM) then it would have changed my PIR placement.

    As for cable runs, I am lucky in that I had a modern house with plasterboard and hollow walls filled with insulation. Therefore, cable runs are relatively easy, I cut a square for the Idratek unit and then use a long drill to make a hole into the ceiling / loft space. Either that or I use existing lighthing cable runs to pull the Cat 5 cabling. If you have got some already then a set of cable rods are a must have.

    Good luck

    Paul

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    Moderator toscal's Avatar
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    For room occupancy you could think about using vibration sensors http://www.sureaction.com/pulsors.htm
    http://www.sureaction.com/MAN-pulsor.pdf
    The pdf gives various ideas for home automation.

    Martin at Automated Outlet sells then Ok he is in the US but with the exchange rate they are quite good value. http://automatedoutlet.com/home.php?cat=123

  5. #5
    Automated Home Legend Karam's Avatar
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    Quote Originally Posted by toscal View Post
    For room occupancy you could think about using vibration sensors http://www.sureaction.com/pulsors.htm
    http://www.sureaction.com/MAN-pulsor.pdf
    The pdf gives various ideas for home automation.

    Martin at Automated Outlet sells then Ok he is in the US but with the exchange rate they are quite good value. http://automatedoutlet.com/home.php?cat=123
    Interesting idea. It looks to me like strain gauge technology (or similar) for measuring beam bending. The way new houses are built I think I'd just need to stick a strain gauge on the ground floor ceilings to get a good indication of upstairs occupancy :-). Come to think of it, the way the house creaks when the heating comes on makes me wonder what sort of joist stresses the sensor would pick up just from heating ..

  6. #6
    Automated Home Legend chris_j_hunter's Avatar
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    >PIR above doors ...

    I was thinking of having them mounted on the lintel, looking down (with a tube to narrow the view) ... is that how yours are ?

    >reed switches ... fast acting ...

    good point !

    >plasterboard and hollow walls ...

    no board in our case, but not plastered yet, or screeded, so not too bad for us at the moment ...

    going to spend the day developing our plastering technique, so should have time to think some more ... having lots of PIRs could get expensive, so need to think carefully about this ... our place will have a minimum of internal doors, so that's another issue !

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    Moderator Gumby's Avatar
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    I have used reed switches typically at the same level as the light switch so that it is very easy to connect to the DRB inputs by drilling straight into the wall box position.

    I also had a brief look at proximity sensors when I was considering how to better detect motion at the bottom of my stairs. The difficulty is that ones that use reflected light have a pretty short detection range - it seems better to either plan on mounting a small corresponding reflector or detector/emitter pairs and use beam breaking (which implies a beam across a doorway rather than down from the lintel).

    However, I then decide to exploit a peculiarity of my stairwell construction to mount a restricted view PIR. You will have to wait for the blog post to see well that turned out :-)

    To mount a PIR - such as the high sensitivity ones used by the Idratek modules - in a tube you would need to carefully calculate length and diameter to ensure that sufficient patches in the beam pattern exist to actually detect motion.
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    Automated Home Legend Paul_B's Avatar
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    Chris,

    I have placed the PIRs above the door header so I guess you could say the lintel. I haven't angled them or anything so they just face into the room.

    One room that doesn't quite work is the ensuite. It is a small room with the presence set to register just 1 second after the door closes it can fail to pickup movement before the light time-out period.

  9. #9
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    Quote Originally Posted by Karam View Post
    For traditional hinge doors magnets and reeds can be placed at the top of the door frame rather than side so you could potential choose to have a door deemed closed even when slightly ajar (we've seen some cases where people wanted this). Internal door sensing can be useful if you're the type of person who regularly closes doors, or you may choose just to sensorise doors that will be shut as part of your security plan
    Hi, just thinking about wiring some (internal) door sensors in and came across this thread. Originally I wasn't going to bother as we don't fully close our downstairs doors - however, mounting them as Karam describes here may be a good option.

    I just wanted to check exactly how this works. For example, if I mount the switch so the contacts meet when the door is still say 30 degrees open (enough to make sure a body can't squeeze around) then I assume the door will register closed. What happens if I continue closing the door - is the door still marked as closed, or is some programming required to get around this?

    Thanks

  10. #10
    Automated Home Legend chris_j_hunter's Avatar
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    not sure I quite understand this approach ... seems to me Cortex would need to understand direction of travel, as well ...

    as an alternative, wonder if a potentiometer or pulse device could work here, ideally within the hinge, but maybe using some string (some sort of loop, or spring-return device, with the string wound around the pot' or strobe-wheel, at some point) ... ?
    Last edited by chris_j_hunter; 7th September 2009 at 11:15 PM.

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