Re: gEDA-user: powermeter board, with less ground planes :-)

[DJ Delorie <dj@xxxxxxxxxxx>]

> Nice job. The only thing left is to decide what to do with the circuit 
> ground. Wherever safety regs permit I always run that straight to all 
> the bolts. Whatever you do never leave that floating about. Same for the 
> enclosure. Of course if the enlosure is plastic this doesn't matter.

On the furnace board, chassis ground and circuit ground were separate,
with a large resistor and small capacitor connecting them.  I didn't
trust all the other wiring in the furnace to be properly grounded
(although, in theory, it's all isolated anyway) so I kept it all
isolated, but the enclosure is all metal so I wanted some connection.

On this one, since the board goes inside a circuit panel box, I'm
thinking of again keeping it all isolated, although ground is
connected back through the USB to the computer doing the monitoring,
so it's not floating.  Non-metallic container, if any (personal use :).
I'm much more worried about accidental shorts than about floating
grounds (the sensors are all isolated too).  Maybe I'll bolt sheets of
clear plastic on the top and bottom of the board to protect it.

> After that it's, as we analog guys always say, "just software". To
> be honest I am afraid you'll have to measure more than just the
> kilowatts.

The goal is to aggregate kWh over time, which would tell me where
opportunities for big savings might be.  After I deal with those, I
can start worrying about smaller savings.  The chip measures the
current many times per 60Hz cycle and integrates the real power used.
I don't yet know how often I'll pull the totals off the chips and log
them though.

> For example you probably want to know pressure curves during the
> time the well pump comes on and how hard it runs as the pressure
> builds.

Ok, that would be cool.


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