[ale] sometimes you just need to reboot NOW!

[Michael H. Warfield]

On Wed, 2014-07-30 at 22:23 -0700, Alex Carver wrote:
> On 2014-07-30 11:02, Jim Kinney wrote:
> 
> > The good part is I can justify getting a BeagleBone Black box as an upgrade
> > to the RasPi :-)
> > 
> > Now if I can do a remote power detection and determine when the room power
> > is running on battery without actually wiring anything to the units...
> > 

> What kind of UPS are they using?  If it's modified sine wave you could
> make a filter that can hunt down the harmonics.  Relatively clean AC
> will have low harmonics.  The modified sine will have very dirty
> harmonics, enough to pick up and distinguish between the two modes.

You might be surprised.  It's been over 20 years since I looked at it
but a simple inverter generating a triangular(ish) waveform into a 3
break point diode shapper gets close enough to a sine wave that the end
result is less than 1% THD without a heavy resonant circuit.  Most
modern UPS with high efficiency switching supplies are significantly
better than that.

> A true sine inverter would be harder to spot.

You're going to be really hard pressed.  Modern units might even
generate cleaner sine waves out of those switching supplies than what
you'll get from the primary power.

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
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