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  1. #1
    Automated Home Lurker
    Join Date
    Jun 2013

    Question LED door lock problem

    Hi all

    First post so be gentle!

    I have begun to set up a system similar to as described here:

    We had some building work done so I laid some cables, both CAT5 and alarm cable. For reasons I can't quite remember I laid 6 core unshielded alarm cable to the kitchen door and the patio door. I also laid CAT5 to various places around the house. These all run back to 'node zero' AKA a patch panel in the utility room in the centre of the house. The alarm cable is not terminated but the CAT5 is.

    So I set up the microswitch in the kitchen door and used a two colour 3mm LED (red/green) in the door frame. The alarm cable is running +ve on white, ground on black. The power source is a phone charger giving +5v with the +ve connected to a 150 ohm resistor. At the door the white comes to the common connection of the switch. The black runs to the central leg on the LED. The a short red wire runs from the NO connection on the red leg of the LED and a short green wire runs from the NC connection on the red leg of the LED.

    This all works great in that the LED lights one colour (red) when the door is locked and the other (green) when it is unlocked. I aim to do the same for the patio door and I have got as far as running the alarm cable.

    I want to 'mimic' the LEDs to a location at the front door as per the link (so I can easily see if both back doors are locked before leaving the house). The problem is that when I connect the red and green wires from the alarm cable feeding the kitchen microswitch (to the NO and NC connections on the microswitch) then the LED no longer glows a clear red or green. It glows a kind of orange all the time but changes shade slightly when the door is locked/unlocked. At this stage the long red and green wires are not terminated at node zero but only on the microswitch.

    So I figure out that there must be some voltage being induced in the cables. The run from the power supply in node zero to the kitchen door is about 8 metres. So I cut the long green cable off the microswitch and the LED goes back to working properly.

    So I google and scratch my head but can't come up with an answer. Lots of other similar problems suggest running twisted pair on the long runs. I wish I had done this in the first place but I didn't and it is completely impractical to replace the cable runs (fresh Karndean stuck to the floor!)

    So I wonder if I can introduce some small circuitry either at node zero or at the door that switches the power to the LEDs. At this point I am a bit lost. My O Level in electronics is a long time ago ...

    There is a bit of space within the door frame for a small PCB. I would be happy to replace the bi-LED with two different LEDs if it helps. I could replace the power supply easily enough as well. The only thing that can't be changed is the cable run.

    Incidentally the cable run from node zero to the front door is CAT5 so I shouldn't have an issue with those LEDs as long as I pick the right colour pairs!

    Would be great to here any suggestions!
    Many thanks
    Last edited by Autobat; 25th June 2013 at 05:35 PM.

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