On Sun, Nov 14, 2010 at 09:42:36PM -0500, Jim Lynch wrote:
> Ben Okopnik wrote:
> >
> > Can't see where you'd need a microprocessor; a timer chip, an op-amp
> > comparator, and a driver transistor should do it - maybe $10 worth of
> > components all together. Feed one side of the comparator from a shunt,
> > and drive the other input from a voltage divider driven by the timer on
> > one end and positive feedback from the output of the comparator on the
> > other. Set the divider so that when the pump is dry, there's not enough
> > drive to kick the comparator on - but when the pump is loaded, the
> > voltage from the shunt is enough to keep the comparator on.
> >
> > As they say, this is untested but should work. :)
>
> The processor I'm using is an $18 part (including a RTC) driving a $2
> mosfet. The added flexibility of sensing when water might be coming in
> faster than usual might be worth the difference. Besides I might find
> other things for the processor to do like monitor battery condition,
> connect via a wireless connection to send me an email that things aren't
> right on the boat when I'm not around, etc.
You could probably even program it to untie the dock lines, raise the
sails, do a little racing, come back, tie up, and put the boat to sleep,
and send you the resulting fun quotient via the G4 network. I'm sure the
iPhone has an app for it. :)
Seriously, though, that sounds pretty cool. 'If the change in water
level in one minute exceeds X, send me an email; if it exceeds Y, send
me a text message; if id exceeds Z, set off a recorded-voice alarm with
the message "this boat is sinking; please alert the marina staff."' You
could make some good money selling those.
--
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