Water level indication

This simple enough?

A floatation ball with simple pully, rope and weight on outside, or simpler still, a transparent hose fitted to the outside of the tank, connected to the bottom leaving the top free mounted to the side. You can then see the level, but not remote like wired system.

ultrasonic units are also made for this type of thing. Much more complicated than you need though.

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A couple of things I've tried and/or considered: Pressure sensors from Freescale Semiconductor Ultrasonic sensors - you can get a pre-jigged modules that are used for robotics Resistance along stainless-steel wire(s) using the circuit on this page

A the moment I'm concentrating on the pressure sensor for monitoring the level of a bore, as it only requires dropping 4mm poly pipe down the bore with a weight on the bottom. The integrated sensors put out a nice 0-5v signal.

Do you know any Instrument Fitters who work in a large industrial plant? If so, maybe they can obtain an old, disused pressure or differential pressure transmitter for you to use as a level transmitter. Then you'd just need a 24v power supply and a remote level indicator. It might be a little bit more hassle than what you are after but its an option.

I was thinking more along the lines of a Pressure Transmitter, like a Rosemount 1151 or 3051, but the pressure sensor is along the same lines.

How about a float with a string around a pulley attached to a multi turn pot and a counterweight on the outside.

Two turns of the string around the pulley to stop it slipping.

Change the pully size to change the ratio between height change and number of turns of the pot.

If that is too easy, get a roller inductor and measure change in inductance instead of resistance.

Use a 555 rigged as an audio oscillator with two insulated metal plates in the tank a few centimetres apart to form the plates of a capacitor, water has a dielectric constant of

you could convert frequency to voltage for a meter circuit to indicate level also. This approach has no moving parts to rust and seize up.

Low cost system with remote digital readout

Regards Pete