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Thread: LED door lock problem

  1. #1
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    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: http://www.automatedhome.co.uk/revie...ator-hack.html

    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
    Ian
    Last edited by Autobat; 25th June 2013 at 04:35 PM.

  2. #2
    Automated Home Guru Vangelis's Avatar
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    Hey Ian,

    Can you post a little circuit drawing as the description is difficult to follow as you say for instance - "the black comes to the common connection of the switch" and then " the black runs to the central leg of the led" assumption is your meaning 'white'. Also not sure what colour wires you are using to make the cable run back to the front door?

    As for induced voltage I don;t think you have an issue unless your alarm cable runs next to some kind of mains cable run. Also are you reducing the voltage at the LED end or at the PSU?

    Vangelis

    EDIT - Just followed link - Is your 'Door Mimic' as per the diagram in the original example?
    Last edited by Vangelis; 25th June 2013 at 03:51 PM.

  3. #3
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    Thanks for your reply.

    Quote Originally Posted by Vangelis View Post
    EDIT - Just followed link - Is your 'Door Mimic' as per the diagram in the original example?
    Yes it is, the diagram is just the same except for using a bi-LED instead of two LEDs.

    There is no mains run near the alarm cable. The voltage is reduced at the PSU end with 150 ohm resistor (but could be either in really, just simpler to do it at PSU I thought)

    Yes, my error on the original, post, I will edit it. The common is fed by the white cable (+ve) and the LED central leg is fed by the black cable (gnd).

  4. #4
    Automated Home Guru Vangelis's Avatar
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    I would have a bash at putting the resistor at the LED end, trying that, and if the same, then ramp up the voltage to 12v (normal alarm sensors work on this voltage) and alter the resistor accordingly, just in case there is any voltage drop on the return (however that shouldn't cause the led to glow Orange, as that indicated a +ve voltage is being seen on both feed legs of the LED.

    Looking at the original cct the design caters for a mimic LED but runs off 12v

    Vangelis

  5. #5
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    I will not get a chance to have a go at this for a little while so looking for a bit more info in the meantime if possible.

    @Vangelis - are you confident your ideas are likely to work or is this a stab in the dark? You sound a little unsure ;o)

    I think the original design is on 12v simply because that was what the guy had on hand. I don't think it matters what voltage is runs on as long as it is pulled down to something suitable for the LED.

    I am trying to get my head around why having the 'mimic wires' connected would make the LED glow both colours simultaneously when only one is actually powered up. I can only surmise it is induction but am not sure. Anyone?

    Ian

  6. #6
    Automated Home Guru Vangelis's Avatar
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    Suggestions were based on minimal disruption (i.e anything but the cable). Without actually being infront of the system it's difficult to surmise what could be the cause as there maybe other factors.

    Using a multimeter should be able to isolate any voltage issues be it drops or induction.

    Suggestion of 12v over 5v was made due to cct design and what is standard in alarm installations (for long cable runs).

  7. #7
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    Thanks Vangelis, good points. I have a reel of the alarm cable so I think what I will do is run a similar length and do some tests with PSU, LED and multimeter to see if I can get to the bottom of what is happening. Once I have some results I'll come back here and update. I am about to go on holiday for a couple of weeks so I'll update after that.
    thanks!

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