Most if not all home sprinkler systems are open-loop, mechanical-based systems that are adjusted manually to output constant water flow that does not take into consideration the current state of the system’s surroundings.
Without checking whether the lawn is moist already from rain, if the weather conditions are appropriate for watering, or if an object is passing the water jet or not, the sprinkler remains active.
With the usual sprinkler parts employed by these products as the base and an attached hose to supply the water, the proposed sprinkler system makes use of valves to control the flow rate in order to avoid objects. When an obstruction approaches the sprinkler within its sensing range, the sprinkler will hinder the water flow in the direction of the object.
The proposed product is an autonomous, weather-controlled sprinkler system utilizing an obstruction sensing and avoidance method. A PIC16F57 microcontroller embedded in a Parallax BASIC Stamp chip will be the CPU of the product. Sensors capable of detecting weather conditions such as a soil moisture, temperature, and light will be interfaced in order for the system to decide when it is appropriate to initiate sprinkling.
Along with a timer integrated circuit, this system will autonomously employ both weather and time control. A series of push buttons and an LCD will also be exploited with a remote controller to allow for human interaction and manual control. Upon completion, the autonomous sprinkler system with object detection and avoidance will prevent what has irritated so many of us for so long in the form of a practical, easy to afford mechatronics solution. Due to slight errors in circuitry and programming, the release of this product is delayed.
Component Selection And Testing:
In order for our product to respond to the weather and its environment, the selection of appropriate and affordable sensors was critical. In order to sense brightness, a photo resistor was chosen because of its simple, variable resistance behavior, its extremely low cost, and its small, unobtrusive size.
Testing this sensor by placing a flashlight at varying distances from the sensor, as well as turning the lights of a room on and off, gave the designers an idea of what the light sensor will output at various times of a typical day. This allowed for the selection of an appropriate capacitor value to use in the sensor’s RC circuit.
Materials & Cost:
If this product was mass produced, the cost to manufacture each unit would be significantly reduced. An essential way of reducing the price is if the Basic Stamp module were replaced by a low to midrange PIC microcontroller with the appropriate amount of memory, computing speed, and digital I/O pins. The temperature sensor could have been replaced by an inexpensive thermistor and controlled using an RC circuit.
The project was constructed as two major subsystems. The first consisted of the
large project box as its foundation, containing the circuit board, the attached motor valve assembly, and the LCD and pushbuttons for human interfacing.
A slot and four buttons were machined in the large project box in order to fit the LCD screen and pushbuttons. Additional holes were machined to accept the wires running from the smaller project box. The selected DC motor was fitted to the water valve using an aluminum C-bar and bolts. A dual power supply is used for the directional control of the motor; 5V is used in order to close the valve and 9V is used to open the valve.
The circuit was designed using Cadsoft Eagle v5.5.0 and etched by first printing the circuit diagram onto photo paper and then transferring the ink from the photo paper to a printed circuit board. After this was done, the components were soldered to the board and the external sensors and devices were attached using jumper wires. The circuit makes use of parallel RC circuits to monitor the varying resistance sensors the pressure sensor, photo resistor, and soil moisture sensor.
Advantages & Disadvantages:
The disadvantages of this product are its cost and its limited range. The limited range of the product was a result of the fact that there simply is not an available market base for affordable distance sensors with a range much longer than 15 feet.
The distance sensors that would have given this product an appropriate range would have utilized laser technology. This would have drastically increased the price to an impractical amount. Another disadvantage is that the motor-valve is only programmed to operate between an open state and a slightly closed state.
The final result of the project was that in the amount of time given to complete the full product, the mechanical and circuit aspects were completely tackled. However, due to changes required in the motor control section of the circuit, the product is capable of successfully reading all sensor output but not able to control the motor.
If given another week, the discrete MOSFETs would have been replaced with relays or a MOSFET H-Bridge IC to perform directional motor control. In the end, some slight adjustments in the program and its flow as well with the motor control part of the circuit would result in a product that could take the readings the project can already obtain and use them towards a successful object avoidance system.
Some future possibilities include increasing the distance sensors’ range, and having a more sophisticated weather control. Currently the PING Distance Sensor’s max range is 3 meters, which would limit this design to small lawns only. With a larger sensing range, the automatic mode of the sprinkler could be used in larger lawns. Improving the weather sensing devices would lend to better timing and watering precision.
Source: Polytechnic Institute of NYU
Authors: Jared Frank | brian Tai | Yuri Shnirman