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Practical Arduino Cool Projects for Open Source Hardware- P24: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | C H A P T E R 12 Water Tank Depth Sensor Water is a precious resource in many parts of the world and many people rely on water tanks to supplement their water supply by storing collected rainwater or water pumped from a well or bore. But how do you measure how full a tank is Tanks are constructed of opaque material to prevent algae growth and are often kept closed up to prevent mosquito infestation or access by rodents so it s inconvenient to physically look inside. And besides having a way to measure tank depth electronically opens up a world of possibilities such as automatic control of pumps to fill tanks when they get low or to disable irrigation systems when not enough water is available. The obvious way to measure tank depth is by placing a series of conductive pickups at various heights inside the tank and measure the resistance between them. For example you could attach ten exposed terminals at equal intervals on a length of material such as PVC tubing and insert it into a tank vertically to measure the depth in 10 percent increments simply by reading the resistance between the bottom terminal and each of the terminals above it. The downside to this approach though is that you ll need to do a lot of wiring and you ll also need to read an analog input for every individual terminal. Also keep in mind that most Arduino designs have no more than six analog inputs. There are ways around this such as using a resistor ladder but it can still end up being quite time-consuming and still give very poor resolution. This project works a little differently. It uses a device called a pressure transducer to measure the water pressure at the bottom of the tank and from that measurement it calculates how full the tank is. Water pressure increases by about 9.8kPa per meter of depth varying slightly depending on the purity of the water and other factors so a full tank 1.5 meters tall will have a pressure at the bottom of about 14.7kPa above ambient atmospheric pressure. The .
