Hi all,

My neighbor and I are trying to find the source of a noise that's=20
bugging us, which is from one of 6 A/C units on the roof above us. It's=20
a periodic hum, plus a noticeable rattle when the thermostat switches=20
off that unit.  I've asked the A/C service guy to check and he says it=20
would take quite some time to monitor for that.

I know it's not my A/C unit as the hum/rattle does not coincide with the=20
operation of my A/C.  Same for my neighbor.  One of the other possible=20
residents is gone for 11+ months each year, and I doubt he'd leave that=20
unit on all year.  So that leaves 3 units. Coordinating with the other=20
residents has been difficult, so I'm thinking I can come up with some=20
sensing device that can remotely alert me as to which unit is switching=20
on/off at any time.  The other complication is that I am not allowed to=20
be on the roof (insured A/C repair persons only), but I can just=20
probably just deploy the sensor with a drone perhaps.

So... what's an easy way to sense this?  Getting a current sensor around=20
the A/C lines will be difficult, but a vibration sensor magnetically=20
attached to the side of the unit should be simple.  I'd think I can=20
create a small circuit with an accelerometer and a processor (perhaps an=20
Arduino), then add some type of wireless transmitter, and a power=20
source.  BTW, power really only needs to last a few days.  And then=20
there's enclosing/waterproofing.

Alternately, I'm wondering if I can mount a wireless camera up there=20
facing all 6 units and vertically attach a stick to the side of each=20
unit and see which one rattles when the A/C goes off.  Assuming the=20
rattle is enough to visually move the stick.  I'm fine with low-tech. =20
Any other ideas.

I really don't have a lot of time for custom circuitry right now. There=20
has to be a simpler way.  Is there some pre-made device I can use to do=20
this, or most of this?

Cheers,
-Neil.

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