robgraham wrote:
On Nov 26, 3:43 pm, robgraham wrote:
My garage is separate from the house by about 20m. There is currently
a bit of a worry about security and I have rigged up a burglar alarm.

It then struck me that it would be a bonus if I could link a smoke
alarm into that too. Electronics is my training so I don't have any
problems in that area, but I've dismantled the smoke alarm (ie got it
out of the plastic !) and am puzzled to see that the piezo sounder
has 3 leads - why ?.

The IC is under the sensor cover - would anyone know if that is
likely to have a dc output rather than the switching one for the
sounder ?

Thanks
Rob

Just to keep this thread going ('bumping' I believe), the smoke alarm
in question is a cheapy from BnQ (~£6) called a Fire Angel. It
dismantles quite easily though the labelling on the back needs to be
ripped off, and the pc board comes out OK - I then desoldered the
ionising device cover and found an IC in there which conveniently
comes up on the web (RE46C122). Pin 2 of this is designed for
triggering other alarms and goes high when the alarm goes off - isn't
that convenient ! There is a track from this pin to the test/hush
switch which will make a good output point.

I haven't tried it yet, but this gives me the 'in' that I wanted -
assuming that there aren't variations on this IC that don't comply
with the data sheet of course !!

Rob

Did you work out why there are 3 cables to the sounder?
--
Adam