[Mark Kelepouris]

That is just a simple float switch.

Actually, thinking about it, a float driving a counterweight over a
pulley that turns a multi-turn pot as a voltage divider into a ADc might
work just as well.

Indeed it would (in theory), but it is expensive to (properly) build and
difficult to maintain such a mechanical contraption surely.

Mark Kelepouris

 

[terryc]

Indeed it would (in theory), but it is expensive to (properly) build
and difficult to maintain such a mechanical contraption surely.

It depends on how flash you want to make it. Something Heath
Rrobinson'ish* shouldn't be too hard to knock up. The hard part would be
driving the pot shaft and the pot would probably be the only thing that
needs replacing. The rest of the electronics would take the same wear and
tear whatever the project.

The counter balance would also be a visible inverse indicator on the
outside.

*If I used something like an old bicycle rim**, the biggest problem would
be the local birdies using it as perch. Given a 27" rim, it would
probably be a direct drive and if I didn't want that much accurracy, I
could probably use that box of 10Mohm pots that can in a lucky dip a few
decades ago.

Hmm, digital? You could block out grey code around the spokes and have it
interrupt a series of opto receivers mounted ontothe old bicycle fork.
wouldn't need a ADC and just drive the parallel port directly.

** Given the right jargon, you could probably call it a "piece of art".

 

[MoiInAust]

That is just a simple float switch.

Actually, thinking about it, a float driving a counterweight over a
pulley that turns a multi-turn pot as a voltage divider into a ADc might
work just as well.

My gut feeling is that no pot track will cope with the constant wear from
such an arrangement and will very quickly wear out.

 

[terryc]

My gut feeling is that no pot track will cope with the constant wear
from such an arrangement and will very quickly wear out.

that might depend on where you are.
Central Australia and dust would be your biggest problem.
For Sydney, I'm lucky to have average a full tank once a month, which
would be less wear than the volume pot on the stereo.

 

[K Ludger]

that might depend on where you are.
Central Australia and dust would be your biggest problem.
For Sydney, I'm lucky to have average a full tank once a month, which
would be less wear than the volume pot on the stereo.

This method is routinely used worldwide for river/ocean/catchment levels. A
quadtrature optical encoders are usually used with wheels in the order of
100 to 300mm diameter. Multistrand steel wire like fishing trace wire is
used. Accuracies to <1mm are achievable. If the counterweight goes under the
water level it is sometimes compensated for, but for a rain water tank it
doesnt really matter. A pot would last for years. Make sure the pot shaft
rotation force is low as possible.

 

[Michael C]

*If I used something like an old bicycle rim**, the biggest problem would
be the local birdies using it as perch. Given a 27" rim, it would
probably be a direct drive and if I didn't want that much accurracy, I
could probably use that box of 10Mohm pots that can in a lucky dip a few
decades ago.

Sounds dead simple but I think I'll stick with the jaycar sensor ;-)

Michael