William Cornutt wrote:
>
> While I have not been keeping up with this string and am not sure of what
 susgestions have been made, here are mine, hope they are not repeats.
>
> First method,
> take all your wife's perals, string them together so the string reaches from
 the top to the bottom of the tank.  The weight of the string will change with
 the depth of water.

  Likewise I haven't been keeping up too well but thought of something
kind of similar..

  Put a spool and line on a stepper motor.  On the end of the line have
a fishing weight and ping-pong ball, coating the weight in epoxy or
don't use lead if it's drinking water.  Pay out the line and it will
magically become lighter when it hits the water.  You could even put the
shaft in a bearing on a strain gague.  Know what the max weight is out
of water and min is with float supporting weight.  Have the motor wind
up and down to keep the strain about halfway in between and you have a
continuous readout.  Could maybe get by without the strain gague.
Microswitch on top and bottom and spring pulling up on shaft instead.
Weight out of water = switch on bottom closed.  Float all in supporting
weight = spring pulling up closes up switch.  Somewhere in between both
switches off and the float/weight will be riding water level.

  Then throw in a big serial eeprom and thermistor to log level and
temp.  Big drop = water use, big gain = pump, little gain = rain (maybe
not so little), little drop with rate following temp = evaporation rate.

  Yeah it's mechanical, but steppers don't fail too often.  And maybe
put a switch at top to pull float up and index occaisionally.  Or
homemade disk/opto simple encoder on shaft or dots on line.  Seal it all
up in a box with only hole out for line and power and you're set.  Get a
motor with right detent torque and only check level and move every 10
secs or minute and power off in between and it should last forever..

  Wow, perfect cheapie strain gague!  Find a worn out RC heli gyro.
Open gyro case and use magnet / hall effect bridge as the scale.
Sensitive enough with relatively light weight and float and low power
stepper motor.

Alan