In South Asian countries agriculture is the major source of economy. Due the lack of rain in the region the irrigation methods are limited and the requirement is to conserve as much water as possible available in a region. The sensor system described in this report analyzes the idea of a water conservation technique for large area of fields using an ultrasonic sensor device. Water conservation is not only a farmer's requirement but also a government need. The idea is targeted towards a region where there is lack of irrigation facilities due to less or no rain. The main competitor of the idea is the rain sensing device that is used in agricultural fields but the idea in this report suits a region where the worst case scenario can be no rain at all. The report will explain the actual problem in detail with an idea to design and implement a system along with the cost requirements.
The water conservation technique mentioned in the executive summary requires a specific irrigation method by which reservoirs are filled up with water. A common and traditional irrigation system in the most of the South Asian region is using a tube well  which is an electrically powered machine that extracts water from an aquifer deep inside the earth and fills it in a reservoir. Generally one reservoir is meant to irrigate one patch (area of 50m x 50m) of a land. A reservoir may be required to fill more than once if the area of field is big and all this has to be done manually. Once the reservoir is completely filled the tube well is turned off manually and then its inlet is opened and water starts moving into the field. This process is time consuming and can lead to reservoir overflow if the tube well is not turned off.
Figure : Shows an ordinary tube well
The task is to prevent wastage of water by preventing any kind of water overflow. The amount of water needed by the farmer can be fed into the sensing system in volumes. This volume check can be done using a sensor device that keeps on detecting the level of the water in the reservoir. The sensor can be placed just beneath grey pipe as shown in the figure so that it points straight down on the reservoir. Once the required water volume is reached, the tube well should be turned off and water outlet should be opened. If the required volume is more than the reservoir volume, the sensor waits till all the water moves into the field through the outlet. Once the reservoir is empty, the outlet is closed and the tube well once again starts pumping the water into the reservoir. This process is repeated until the desired volume is reached.
Without this sensing technique the farmer might have to wait for a long time (depending on the flow of water from the tube well) before all the fields are irrigated. This sensing technique save a lot of time and water and it needs to be installed along with the complete irrigation system (i.e. reservoir, tube well). This system is designed for the people in farming and agriculture. The system is more efficient if there is a vast area of land to be irrigated as it takes more time to this manually. Moreover the main purpose of this system is to conserve water and electricity and therefore the sensing device on the tube well can be financially sponsored if approved by the government.
2.1 System Specification
Some of the system specifications are given below.
Ultrasonic Senor to detect the level of water
A Keypad to input the water quantity in either in volumes.
A microcontroller to control outlet valve opening and closing. It also controls the motor running tube well.
Once the system gathers the information regarding the volume of the water, the farmer can then go on to do some other work without worrying about any wastage of water and electricity.
2.2 Development Costs
The total budget of the sensing device should not be more than a fraction of the total cost of the irrigation system.
Tube Well Motor- $1000-$10000 (depending on motor Horsepower), Reservoir Tank - $500- $2000 (depending on size)
The cost of the sensing equipment and other controls are
Ultrasonic Water Sensor - $400
Keypad control - $20
Other Costs -$50
The overall price for the sensor mechanism is around $520 which is about 14.05% the cost of an average tube well system ($3000 tube well + $700 reservoir = $3700).The effectiveness of the system is much more than its price and it can be a very cost efficient system keeping in mind the electricity consumed by the motor.
3 Review and Current State of art
Water Detection techniques using sensors have been implemented in quite different ways. The design described is this report has a different strategy which is water conservation using water level detection. There are other methods that already in practice which uses sensors to preserve water. Most of the methods are based on water sensing methods. The sensor basically detects the water and then it can either activate an alarm or close the supply of water. They can be either be wired or wireless.
One of the water conservation techniques is the "Rain-Activated Sprinkler Shut-Off System" . This system (U.S. Patent 5087886) works in a similar way as described earlier. The Sensor on the sprinkler detects a certain amount of rainfall and then shuts down the water supply from the sprinkler. Another sensor technique widely implemented is the Wireless Rain-ClickTM Rain Sensor. This sensor is developed under U.S. Patent 6570109 B2 (Quick Shut-Off extended range hygroscopic rain sensor for irrigation systems) . In simple words this sensor has a hygroscopic disc that detects rainfall and with a mechanical action is able to stop the irrigation supply once it has rained sufficiently. Once the disc becomes dry for some time which means there has been no rain for quite some time, the irrigation is supply is turned on . These applications are more specific towards water conservation in case of rainfall.
The system mentioned in this report is quite unique and is more effective in areas where there is shortage of water for irrigation purposes. The functionality of this design depends on the measurement done by the ultrasonic sensor. The sensor detects the water level/volume in the reservoir and once the target water level has reached, the reservoir outlet opens and the water starts moving out in the field. The ultrasonic sensor is used here because it is easy to install and its price is well within the budget. There are also other methods by which the water level of reservoir can measured, one of which is using a submersible cable sensor. These sensors are cheaper than the ultrasonic sensor and are best used for deeper areas but they have two major drawbacks. Firstly, they only offer basic features  and secondly they are not compatible with most of the interfaces and microcontrollers. Moreover the ultrasonic sensor is a non contact sensor and uses the latest technology to provide highly accurate results for low to medium level depth areas.
4 Preferred Design and Implementation
The ultrasonic sensor uses a transducer to convert the electrical energy to sound energy and vice versa and its working is pretty much similar to that of a sonar system used in submarines. In this system the high frequency ultrasonic waves are emitted towards the bottom of the reservoir and these waves get reflected from the water surface are received back by the sensor. The senor calculates the time duration between the transmission and reception and can then measure the water level.
4.1 Quantitative Specification and Design Detail
The average dimension of a reservoir is 6ft x 5ft x 6ft and the sensor would be placed just beneath the pump at about 1ft from the top of the reservoir. The line of sight of the sensor should be free of obstacles for accurate results. The sensor used here is waterproof and there is no need for any special protection. The waves are sent out with the speed of sound (330 m/s) but a change in the atmosphere (temperature, humidity etc) can alter the speed of sound and produce inaccurate results. This issue can be dealt by proper calibration of the system.
Figure : System Specification
The overall weight of the ultrasonic sensor transducer should not be more than 700 grams. The sensor is controlled by a microcontroller which controls the tube well motor and the reservoir outlet.
The user can input the required volume of water through the keypad and can then start the operation. The total distance travelled by the ultrasonic waves will be the distance from the sensor to the water surface and back to the sensor which comes out to be (removes the error). The total distance can be calculated by. The distance is halved and then 2 feet distance is subtracted from it to give the actual distance between the water surface and the reservoir top. The water level can be calculated by subtracting the "actual distance" from the height of the reservoir. Once the water level is know then the volume of the water can be can be calculated as The sensing mechanism will require some wiring from the microcontroller to the sensor, outlet and the motor and should not be more than $20. The sensor being used consists of both the transmitter and receiver so there is no need for separate specifications. The microcontroller needs to programmed and powered by the main supply and it is the control mechanism for sensor, outlet and the motor.
The transducer embedded in the sensor is the piezo transducer which emits the ultrasonic waves in the form of cone using the piezo effect. They are much cheaper and efficient than their counterparts and hence used here. The microcontroller receives the water level from the senor and can then calculate the volume of water in the reservoir. If the reservoir becomes full and the desired volume not attained, the microcontroller shuts down water supply to reservoir and opens the outlet to release the water. At this moment the sensor again starts to check the water level and once the reservoir is empty, the sensor notifies the microcontroller which in turns closes the outlet and starts the water supply again. This process is performed till the desired volume is achieved.
Figure : System Process List
4.3 Performance and Accuracy
The performance of the sensor relies on the environment around. An average ultrasonic sensor can work in temperatures from -100C to 700C producing an average accuracy of 1.0% for a depth of 6-10 ft. Performance can be affected by obstructing the path of the ultrasonic waves and therefore the sensor should be installed at an appropriate place ( below the tube well pipe).
5 Prototype Delivery
The full working prototype can be constructed within 30-35 days. Purchasing a tube well mechanism with a reservoir will cost around $3700 .The construction would involve embedding and programming the sensor system and the keypad ($20) with the microcontroller ($50). It can be developed and tested in about 30 days time. In the final part of the development the reservoir dimensions are coded into the prototype and the sensor is firmly installed on the tube well pipe. Finally, the connections to the motor and the outlet are made with the final test being performed on site. The reservoir implemented here is a metallic water tank but in some places the reservoirs are constructed using bricks which mean that final part of the development needs to be done on the site of the reservoir. The labour on this should not be more than $70.
The successful implementation of the sensor system will save farmer's time by automatically handling the pumping of the water into the reservoir and then onto the fields. It will also save electricity as the motor will only be turned on when required thereby conserving water. The system can be of a great success in place where there is shortage of water and electricity. The sensor seems to be a bit expensive in the beginning but if this idea is approved and implemented, and then this might bring competition from other tube well companies. Having competitors in the same field would eventually lead to the purchase of bulks of ultrasonic sensors thereby reducing their price per unit.
Figure : Screen shot of the Patent  (Rain activated sprinkler)
Figure : Screenshot of Patent  (Hygroscopic Rain Sensor for Irrigation