This would be a good application for Dallas one-wire devices.  I believe there
is one device which has a temperature sensor, and a one bit input.  All of these
devices have unique addresses (2^64 or something like that), and get both power
and data on one line, with multiple devices connected to one line.

It would also give you the temp at each smoke detector, augmenting your system.
You can tell where the smoke is, and you can also tell where the heat is.

-Adam

Rod Phillips wrote:
>
> Hello to all,
>
> I  want to design a small fire alarm panel for my home, to augment my
> existing alarms, using some sort of addressing scheme for the smoke
> detectors.  I plan to use two wire detectors that short the line when in
> alarm.  I had debated using a voltage divider system with a current limiting
> line resistor as the top half, and different values of resistance between
> each detector and the line as the bottom half.  I would then use the 16c72's
> A/D capability to read the divider and determine which head(s) were in
> alarm.  Does anyone have an idea how to do this differently - possibly using
> some sort of addressing scheme?  I know addressable detectors are available,
> but I assume the algorithm used to read these is proprietory.
>
> I will also need to keep a 12 volt, 10ah, lead/acid battery charged and
> would appreciate any ideas here.
>
> Thanks in advance for your ideas.
>
> Rod
>
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