On Thu, May 21, 2009 at 6:18 PM, Alan B. Pearce <Alan.B.Pearce@stfc.ac.uk>wrote:

> >Let's say there are 16 such sensors.  Running a bundle of 16 pairs
> >of wires around seems... awkward.  Certainly they could share a common
> >ground, so that's down to 17 wires at the controller, down to two at
> >the last sensor...  16 comparators into a multiplexer, and have the
> >controller scan them every pass through the event loop.  Something
> >like that.  Is that the best we can do?  Maybe an analog multiplexer
> >and one comparator?
>
> Right, for sensors, especially drip sensors, my initial reaction is to make
> a PCB with fine tracks and fine spacing, without solder resist. With the
> RoHS fanaticism that is currently around, one of the finishes you can get
> is
> a gold flash, which would seem to me, to be a suitable method to protect
> the
> copper. Then a small micro can sense moisture bridging the tracks by the
> conductivity of a drop of water, and with salt water this shouldn't be a
> problem.
>
> Could you make a bunch of those by cutting up the edge connector from an
old isa/pci card?
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