Home Security System - Part 3

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Home Security System - Part 3


Unable to find locally the little 'recessed security window magnetic reed switch' so I went to Radio Shack and bought some magnets, with the idea being that I will place the magnet on each of the sensors on the windows downstairs and then see if I get any continuity at the system box.

Update
I was able to buy 10 magnets at Radio Shack for about $6.00 for testing.

A brief note: Windows and doors typically use a simple sensor - it's typically a reed switch that can be closed (electrically like turning a light switch to 'on') by the presence of a magnet; removing the magnet causes the reed switch to 'open' (electrically like turning a light switch to 'off').

What I had observed on the windows was a little circular tab (the reed switch and wires) on the casement of the window sill, under the window pane itself.  There should have been a magnet installed on the wooden frame of the window pane, but the builder had not installed these.  Normally, opening the window by sliding the window pane up, with the magnet attached, would pull the magnet away from the reed switch and the circuit would be electrically open, which typically is the alarm function.

An installer has a choice when installing the sensors; they can 'daisy chain' the sensors together, so in the case (like ours) where we have 5 windows side-by-side (in the sun-room; the rest of house windows are also wired), the wire would go window-sensor to window-sensor, and after all 5 had been been joined, a single wire would be taken down the security box.  This would have meant that, if any one window, or any combination of windows including all windows, had been opened, then the circuit would be open.  This would mean there's no way to determine which window was opened, just that one or more of the windows on that daisy chain had been opened.  The benefit to this approach is (from your view) is that this constitutes a zone, and it will only take up one sensor slot on your security motherboard.   So, in this case where I have 5 windows, it would have taken up just one sensor slot on the security mother board.  And since they are all side-by-side windows, I don't care about which window might be in alarm, just interested in knowing that one of these windows - any one, is in alarm. So this would be a good area for a daisy chain, and a 'zone'.

Another way to wire this is to have each window have it's own individual wire go down to the security box.  This way, you know which individual window was opened.  But this means you would have to use 1 sensor slot per window sensor.  So you get more detailed information (which individual window is alarming), but at the cost of more slots used on your security motherboard.  As it turns out, my windows were individually wired this way; I was expecting daisy chain, but instead it was wired for each window to be sensed.  So all 5 wires were pulled to my security motherboard.

Since most security motherboards have a limited number of sensor-slots, it is usually the case that you won't want to sense the individual window.  For example, my DSC 1500/1550 motherboard only has 6 sensor slots total.  So, if I were to wire up each of my 5 windows to an individual slot on the security motherboard, then that would just leave me 1 more slot for the entire rest of the house!  Not what I want.

Note: For the following to be clear, we need to make a distinction between a wire.  In this case, when I'm referring to a wire, it's referring to the 2-conductor wire that goes from the window sensor to the security box.  Inside of this wire are 2 conductor wires, which I'll refer to as conductor 1 and conductor 2.  So a wire, in this case is what goes from the sensor to the security box, and this wire has 2 conductors.


So down at the security box, where all of my wires come in, I'm going to have to join each of the 5 wires from the window sensors into a daisy chain.  This means I will take, starting with the first window sensor wire (each of these wires are a 2-conductor wire), I will take one of the conductors and join it with one conductor from the second window sensor wire.  So I'm joining a conductor from wire 1 to a conduct from wire 2.  Then from this 2nd sensor wire, I will take the second conductor and join it with a conductor from wire 3.  So at this point, I've got 3 sensors daisy chained together: wire 1 conductor 1 is joined to wire 2 conductor 1, and wire 2 conductor 2 is joined to wire 3 conductor 1.  I will join wire 4 to wire 3 in this manner, and wire 5 to wire 4 in this manner.  When I am finished, I will have 1 conductor from wire 1, and 1 conductor from wire 5, left over; these are the beginning and the end of the daisy chain.  These 2 wires are the ones that will be connected to the sensor slot on the security motherboard, and will allow the security mother board to detect any window opening in the daisy chain on that slot.

This will occupy 1 slot on my security motherboard.

Since my system only has 6 slots total available, I've used up 1 slot, or 1/6, or 16.6% of my available slots just on the windows in the sun room.  So, I may decide to add some other windows that are close by to this zone.  For instance, the sun room has a door to the outside porch.  Since it's in the same area as the windows, I may decide that I don't care about being able to differentiate between this door and those windows being open, in which case I'll add the door to the daisy chain at the security box.  However, if I want the door separate, than I won't want to add this door to the daisy chain, and would add it to it's own individual slot.

So the determination I'm faced with: a) I have 6 sensor slots total, and I have a lot of windows, and a lot of doors in this house, which means some windows are going to have to be daisy chained, and maybe some doors.  b) I want to, at least, know that a certain area of the house has gone into alarm, rather than the whole house just being a jumbled up mess - I would like to know the area that is in alarm.  So I will probably daisy chain the sensors in a common area together.  This means I will probably join the sun room windows sensors with the sun room exterior door, along with two other close by windows in the den; this would mean I have 7 windows and 1 door joined together.  This is the approach I'm going to have to take throughout the house in able to be able to detect with just 6 slots.


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