On Wed, Mar 24, 2004 at 01:20:07PM +0200, Lucian wrote:
> The idea is that the system has to work with a variety of sensors
> (powered at around 12V) and I don't use a particular sensor. It it about
> PIRs, but can also be smoke detectors and all sort.

It would be helpful to know if they require a regulated 12V. But I'm almost
certain that alarm sensors can be run from a 13.8V battery voltage as they
all have regulators internal to the sensor itself.

> I realised that the
> voltage for the comparators is not an issue anymore, as I'm using a
> voltage divider, so the 12V can be around 10V-14V without any problem.

I'm still trying to resolve why it is that the comparators need anything
other than 5V to do their jobs.

> Am I mistaking ?

Still not enough information because you haven't yet told us why you are
using the comparators.

Let me give you an example. I have a wire loop for the doors. Because of the
length of the loop I power it with 12V. Instead of a comparator at panel,
I connect the loop across the LED in a optoisolator (using an appropriate
current limiting resistor), then drive the output transistor of the opto
from 5V.

Now the loop is powered from the unregulated line/battery voltage and the
optoisolator converts that voltage to 5V. Poof! only one regulator is needed.

You could do something like that if you can give more information on the
purpose of the comparators. If they are just there for level conversion, then
there are other ways to solve the problem.

The key point here is that you want 2 voltages: 13.8V unregulated, 5V
regulated. In our continuing discussion I still get the feeling that you want
to regulate the line/battery voltage, when it's probably unnecessary.

BAJ

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