Water is a hot topic around these parts. It has been dreadfully dry and so we are doing everything we can to manage our water. Part of this is measuring how much we have and how quickly we are using it. Enter my old friend the Arduino, that I've done a few things with recently.  I had been playing around with techniques to sense the level of water in a tank, and had a few designs, some using capacitive techniques, others using an ultrasonic transducer.  All of them had some level of issue, so I decided to get a pressure sensor and build it around that.

Water pressure varies predictably with depth, so a pressure sensor is very easy to use to determine the level of water in a tank.  The one I chose was a cheap Chinese pressure sensor that is designed for higher pressures than I had in mind, but still does a reasonable job for what I was after.  With a well-matched sensor I should have been able to get millimetre accuracy, with the cheap model I am getting 5cm (2") resolution.  Good enough for a tank sensor though.

The first prototype is hooked up inside the pump house for the garden/animal pens.  The ribbon cable at the top leads through the wall to a XBee radio transceiver which sends tank readings back to the house.

The closeup shows that I'd used protyping board and a Pro Mini board.  The right-hand black cable goes to a power adapter and the left-hand black cable to the pressure sensor.

Once I had the idea worked out I built one for the house tank in a slightly more weatherproof enclosure.  This one is driven by a 12v battery and solar panel.  The pressure sensor has a 1/4" thread so I drilled and tapped out the tee joint. It does mean that there are minor pressure changes when the water is flowing but in practice it has negligible effect on the measurement.  The three LEDs provide a quick visual check, with red showing at below 20% capacity and green when it gets above 60%.

Next step is to analyse the logs and start to build a usage profile.