I would like to be able to measure the level of water in 8 barrels. The height of the barrels is around 1.2m.

My first thought, was to use float switches, 8 per barrel at constant positions which would give me an empty, full, and 6 stops in between. This could be combined with a binary encoder per barrel, giving me 8 inputs (one binary per barrel) that could be read by a single PIC chip and displayed as percentages on an LCD screen.

However, cheapest float switches I have been able to find have been on fleabay, at £0.99 plus £2.50 postage, which would mean (even if postage were combined), a starting price >£64 for the 8 barrels.
Would there be a cheaper or simpler way of achieving this? (Bearing in mind I am UK based the costs would be different to US stores), but simpler ways?

The liquid is dirty water, I would have 12V and 5V available as 'standard'. I tried a 12V pump in them last week, without properly waterproofing one of the contacts (GND), this had corroded within an hour, which make me think that trying to make a resistive based float device may not be particularly doable.

 

Maybe I should also state that empty any full are the two most important states.

 

When you say "dirty water" what exactly do you mean?

 

Pressure sensors sunk to the bottom? Some sort of weight based system where you measure the deflection of the supports? Ultrasonic distance measuring from the top?

 

You could use a strain gauge on the bottom of the barrels and use the weight as your level sensing.

 

By dirty water, it is rain water, but not well looked after. Algae etc. brown sludge. This would make a capacitance/resistance type system inaccurate I think.
The issue with using the weight of the barrel would be it is likely to be between 0 to 200L, which is a 200KG difference. It would be difficult to accurately determine the empty and full states I suspect, meaning I would probably need to put float switches in for those states anyway.
The ultrasonic distance measuring would seem feasible, but when I read other posts, the impression I got was that reflections could cause issues?

 

You would sample the utlrasonic readings and use the average over...say a minute.

Do if the wind blew and caused ripples, it would change for a few seconds, but the processor would sample a few times a second and average the level, then report to the LCD every minute (or faster if need be)

I think the weight is the best way to go.

3 components. strain gauge, opamp and ADC. (which you can get onboard the uC)

I would use the weight, than a float for FULL. If you know how much the barrels weigh empty, thats easy to do.

A simple foam float to microswitch can be your full indicator. the microswitch can and should be out of the water, or use the ones that are used with sump pumps. A sturdy guide wire to the water level where you attach the foam, then you have a under $1 solution for full. The weight way should be under $5 per barrel.

If you are going to use the full float to turn off a pump or close a valve that feeds/fills the barrel, I would definitely use a microswitch for the full.

 

Hello,

Here is a page with several ideas on measuring levels:
http://www.iceweb.com.au/Technical/LevelTechnologies.html

This is a page from the EDUCYPEDIA page on Miscellaneous sensors:
http://www.educypedia.be/electronics/sensorsmis.htm

Bertus

 

Why not do what they do in RVs? Put some electrodes in at various levels and measure the resistance between them. Works with clean and dirty water. Cheap, but you'll have to build some electronics to deal with the signals.

For an electrode, I'd use a screw through a stick. Clamp a wire between two nuts, then dip things in e.g. wax to insulate things a bit and keep the water from corroding the wire/screw junction. If you want to make it even simpler, drive a nail through the stick and solder the wire to the nail (use copper nails if you can find them). Then insulate with wax/epoxy/etc. to avoid water contact with the joint and water getting under the insulation.

 

Here's another link to a site with information.

A dozen ways to measure fluid levels

 

Hang a metal or plastic rod into the water and use some kind of device (can be the kind designed by Heath Robinson) to measure its apparent weight. I say "apparent" because the more deeply into the water that the rod is immersed, the lighter it will appear to be. No liquid contact of electrical parts needed!