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Microscan AN214 + pager, car alarm ,diy fitting

I wanted advanced warning *before* anything is damaged via the pager
and the AN214 + pager can be setup to do this via the "door warning"
(evidently you loose the original door switch trigger: but by then,
it's too late!).

I wired the piezo output into the TX door-warning negative trigger and
it worked OK but I also had to add a 1K resistor pullup because the
additional load of the TX input pulled the microwave output down a
little, about 0.6V, and this was enough to start the piezo whining (I
measure a current draw of 360uA equating roughly to 33k pull down
against a 2k2 pull up).

I had one problem: The controller provides an active-low output to
turn on accessories i.e. the microwave sensor and the TX (so that when
the alarm is turned off, everything else is shut down too). I was
forced to disconnect this from the TX and use the switch (optionally
provided as piezo disable) as a manual TX on which is a mild
inconvenience because you have to remember to switch it on about five
minutes before enabling the alarm (or leave it on all the time).

I had to do this because, after the TX is enabled, it sends a
"phone-home test" every fifteen seconds for about five minutes and
this occasionally triggers the microwave module setting off the main
alarm even when it is fully turned down. After the TX has settled, the
output it sends whenever the door-trigger is asserted does not affect
the microwave module.

The TX and microwave device are fairly close: driver's side windscreen
bottom corner to right side of cigar lighter (driver's left knee). I
tried a half hearted attempt with a ferrite on TX and then microwave
module (the interaction was intermittent so the slightest change in
the right direction should show some difference) with no effect so my
guess is that the interaction is radiated, not lineborne.

When the TX does the fifteen second thing, it is extremely energetic
i.e. you can hear it audibly vibrate (and my hearing is 17dBs down at
2kHz). This does not happen during the "door warning" transmission.

This setup is very stable, insects, wind have no effect on the
microwave module. The pager has a handy clip on its sturdy aerial (and
a belt clip for the pager itself).

A 1Km TX to pager range is claimed.


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