🚀 go-pugleaf

In article <1992Dec29.175243.10083@cbnews.cb.att.com>, wrb@cbnews.cb.att.com 
(wallace.r.blackburn) writes:
> In article <1hq0ilINNbji@fnnews.fnal.gov> behnke@FNALF.FNAL.GOV writes:
>>In article <00965764.D96DDB80@Msu.oscs.montana.edu>, uchrgrh@Msu.oscs.montana.edu writes:
>>>I would like to build a solid state device that would turn off a water
>>>pump in my aquarium if the water level drops  below a certain level.
>>>I am willing to look at prefabricated stuff but would prefer to build it
>>>my self.
>>
>>Seems that a simple micro-switch attached to a float would work fine.  [...]
> 
> HEY!!!!  That would be simple, functional, and reliable!  What the heck are
> you trying to do here?!
> 
> I was going to answer this in a few weeks.  I wanted to get the results of
> the modeling and reliability studies first.  Since I'm on the spot though,
> I'll give the preliminaries.
> 
> First, for reliability, you definitely need multiple sensors.  Three
> should be sufficient.  These will each be monitored by separate
> microcontrollers and the results sent to a master contoller via a duplexed
> serial link.  Some more work will have to be done to determine the optimal
> protocol for the link and so on.  Most probably have to develop an entirely
> new one.

I thought this was sci.electronics.  This last bit sounds like comp.mail.uucp .
:-)

However, the best microcontroller-based design cannot make up for poor sensors.
And as long as we're going to all this trouble, we should ensure that the
design is robust enough to stand up to marine environments (e.g. for salt-water
aquariums, aquatic parks, etc.).  I doubt that the float-and-microswitch
arrangement qualifies on this point.  

Obviously, the best solution is to use Polaroid ultrasonic ranging modules to
determine the height of the liquid in the tank.  These will have no problems
with corroding pivot-points nor with corroding sensor probes, etc., and in fact
will be completely noninvasive (unless the tank occupants are sensitive to
ultrasonics; hmm, better check out the freq. range of dolphin hearing, among
others). 

Best of all, since you now will have not just a simple on-off sensor but rather
a continuous range of values, your microcontrollers can keep a record of the
water height over time.  You can use this to figure out the optimal times to
add water to the tank.  Who knows, the movements of various fish may produce
recognizable "signatures" in the ripple patterns on the top of the water, and
you could collect this information and analyze fish activity levels over time.

Probably two or three research grants' worth of work right there.  

:-)

	--- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA
Internet:  jeh@cmkrnl.com, hanrahan@eisner.decus.org, or jeh@crash.cts.com
Uucp:  ...{crash,eisner,uunet}!cmkrnl!jeh