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Design of Trickle Irrigation Control Unit using PSoC

 Nandakumar.R , K.S.Lalmohan, Sreejeesh.S.GVLSI Design Group, DOEACC Centre Calicut, INDIA

Email: {nanda, lalmohan, sreejesh}@doeacccalicut.ac.in

 Abstract  — Prolonged periods of dry climatic conditions due

to fluctuation in annual precipitation, may appreciably

reduce the yield of the cultivation. The expenses in

establishing many of these crops and their relative

intolerance to drought make an effective irrigation system

a necessity for profitable enterprises. The fact thatmajority of the crops are planted in widely spaced rows

and require soil water content to be maintained at

relatively high levels, makes them well adapted to trickle

irrigation. This paper proposes a System level design of a

PSoC based control unit for trickle irrigation system

 Keywords— PSoC, Trickle Irrigration, Drip Irrigation,

Irrigation Automation Systems 

I.  I NTRODUCTION 

Drip or trickle irrigation refers to the frequent application ofsmall quantities of water at low flow rates and pressures.

Rather than irrigating the entire field surface, as withsprinklers, drip irrigation [2] is capable of delivering water

 precisely at the plant where nearly all of the water can be used

for plant growth. Because very little water spreads to the soil between the crop rows, little water is wasted in supporting

surface evaporation or weed growth. The uniformity of

application is not affected by wind because the water is

applied at or below the ground surface. A well designed andmaintained drip irrigation system is capable of an applicationefficiency of 90 percent. The trickle irrigation system with the

 proposed control unit offers the following advantages

1.  Reduced Weed germination: Water is directed to the

crop, leaving the area between the rows dry, so weedseeds located there are less likely to germinate

2.  Fewer leaf diseases occur: Wet leaves encouragefungal and bacterial plant diseases. Trickle irrigation

does not wet leaves

3.  Uniform Wetting patterns can be are achieved: In

contrast, overhead irrigation allows the wind toevaporate water and distort wetting patterns

4.  Soil structure is not damaged from water falling on

 bare soil

5.  Insecticide and fungicide use is reduced. Trickle

irrigation does not wash pesticides from the foliage.

6.  Quantity of water used is reduced: Plants need the

same amount of water no matter what the delivery

method. Trickle irrigation places the water at theroots, where plants can use it best

II.  TRICKLE IRRIGATION LAYOUT

FIGURE 1 TYPICAL TRICKLE IRRIGATION LAYOUT

The arrangement of components in figure 1 represents a

typical layout. Variations in pressure[3] within the system dueto changes in elevation and pressure loss within the pipes will

affect the discharge of individual emitters. For a system to

irrigate satisfactorily the application of water must be uniform.

There should be no more than a 10 percent variation in

discharge between the emitters with the lowest and highestoutput. To achieve this, pipes and tubing must be sized

correctly. Laterals should run across slope, following contour

lines or run slightly downhill. Areas of a field at different

elevations should operate as separate sub-units with separate

 pressure regulators. The typical line source emitter [1] is twin-wall tubing, with two pipe chambers. The larger, inner

chamber is for water flow along the row length. The smaller

outer chamber has the pressure dissipating emitting device.

2009 International Conference on Advances in Computing, Control, and Telecommunication Technologies

978-0-7695-3915-7/09 $26.00 © 2009 IEEE

DOI 10.1109/ACT.2009.24

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III.  PSOC TECHNOLOGY

The proposed design utilizes [4] Programmable System OnChip platform by Cypress Semiconductor. One PSoC mixed-

signal array integrates a Microcontroller with as many as 100

 peripheral functions. It provides low cost design through

reduced chip counts streamlined manufacturability, and

improved power efficiency.

The PSoC comprises a built-in MCU with flash memory and

SRAM link to essential system resources

•Sleep and watchdog timers•Multiple clock sources that include a PLL

•Internal main and low-speed oscillator

• External crystal oscillator for precision, programmable

clocking

PSoC devices can have upto two multiply & accumulators

(MACs), which provide fast 8-bit multipliers or fast 8-bit

multipliers with 32-bit accumulate, up to two decimators for

digital signal processing applications, I2C functionality for

implementing either I2

C slave or master, and availability of afull-speed USB interface

FIGURE 2 PSoC TOP LEVEL ARCHITECTURE

PSoC mixed-signal arrays free designers to route any signal to

any pin, shedding the constraints of a fixed peripheral

controller. In addition, global buses allow for

signal multiplexing and for performing logic operations,

eliminating the need for a complicated digital-logic gate

design.

IV.  PSOC BASED DESIGN

The distributed sensor system [example WSN] collects details

of parameters like moisture content and temperature fromdifferent sectors of the field. The signal send by the sensor is

 boosted up to the required level by corresponding amplifier

stages. This is further fed to A/D converter modules inside the

PSoC of desired resolution to obtain digital form of sensed

input for microcontroller core, which can be used in the

system to monitor sensed values and the current status ofrespective valves with the help of a LCD module. The

solenoid valves are controlled by microcontroller core

through relay drivers. A Chemical injection unit is used to mix

required amount of fertilizers, pesticides, and nutrients with

water, whenever required. This is again controlled by the MCcore based on a Look Up Table, programmed in. The LUT isalso programmed with PWM output rating corresponding to

the sensed value of temperature and pressure. As per the duty

cycle of the PWM output the speed pump motor can be varied

which further controls pressure of water. A flow meter is

attached for analysis of total water consumed. The requiredreadings can be transferred to the Centralized Computer for

further analytical studies, through the serial port present in the

PSoC. The in-built timer in PSoC can be configured, to

operate parallel with sensor system. In case of sensor failure

the timer turns off the valves after a threshold level of time,

which may prevent further disaster. The control unit may thenwarn about the pump failure or insufficient amount of water

input with the help of flow meter which is fed back to the MCcore for adjusting motor speed to control the injection rate

accordingly. The MC core controls the relay driver to control

the valves which are connected to the drip lines fitted with

emitters. The lateral drip tapes are polyethylene tapes with built in emitters. They are available in a variety of diameters,

wall thicknesses, emitter spacings and flow rates.

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The choice of emitter spacing and flow rate is determined by

crop demand and soil-water holding capacity. Tape diameter,

available flow rate and elevation changes determine themaximum lateral length that can be used. This should not be

exceeded as emitter flow rate variation will increase and this

will affect crop performance.

V.  DESIGN CONSIDERATIONS

The hours of operation needed to meet the irrigation

requirement will depend upon the flow rate of the emittingdevice, the irrigation interval, and the rate of consumptive

water use by the crop.

When computing the daily water requirement, the calculations

are based only on the area of the field that is actually covered by vegetation. This is possible because only the vegetated area

is irrigated with trickle irrigation systems. For example, if a

crop is planted in rows that are five feet apart but the

vegetation is only three feet wide, 100 feet of row length

would have an area of 300 square feet, not 500 square feet .It

is assumed that the un-vegetated strip between rows uses nowater and is not irrigated. If the crops were estimated to

require 0.25 inch of water per day, the daily water requirement

would be 52.5 gallons per day per 100 feet of row length. This

answer is given by,Q = 0.7 W L D

Where

Q = daily water requirement, in litre

W = row width of vegetation, in meter

L = length of row, meter

D = depth of water use by crop, cm/day0.7 = constant (includes 90% efficiency)

If the crops are to be irrigated every two days by drip tubing

that emits 0.5 Litre pm per 100 m of length, the operating timefor the system would be 3.5 hours per irrigation. This is

determined from the equation:

T = Q I /R

Where

T = operating time, minutes/irrigation

Q = water requirement, Litres/day/100 m of row

I = interval between irrigations, days

R = application rate of tubing, lpm/100 m

The required operation time per irrigation will be given

 by,

T = Q/N R

Where

T = Time of operation, hours/dayQ = Water requirement, L/tree-day

 N = Number of emitters per tree

R = Emitter flow rate, L/hour

The area that can be irrigated is determined using availablewater supply capacity and the average available pumpinghours as

Area (ha) = Flow rate (L/hr) x Pumping hours (Hours/Day)10K X Gross Irrigation Capacity Required (mm/day)

Also, the flow rate is determined as

Flow rate (L/ha) = Number of emitters/ha x Emitter flow rate

Based on this computation the LUT inside the MC Core

residing in the PSoC need to be programmed to adapt the

PWM duty cycle, so as to control the motor speed.

VI.  CONCLUSION

Trickle irrigation can be an extremely versatile production toolin horticultural enterprises. It can stretch limited water supply

to cover up to 25 percent more acreage than a typical sprinklersystem. It can reduce the incidence of many fungal diseases by

reducing humidity in the crop canopy and keeping foliage dry.

It allows automation of the irrigation system, reducing labor

requirements. It delays the onset of salinity problems when

irrigation water of marginal quality must be used .A system

level design of the control unit for automating trickle irrigationsystem based on Programmable System On Chip is proposed,

which offers high level of re-configurability and low

manufacturing cost.

R EFERENCES 

[1]  Keller, J. and David Karmeli. 1974. "Trickle IrrigationDesign," Rain Bird Sprinkler Manufacturing Company,Glendora, California, 182 pp

[2]  R.W Hill , J.Keller 1978 , “Irrigation system selection formaximum crop profit”,  Proceedings of the 10thconference on Winter simulation - Volume 2, Pages: 495 -504

[3] M.A. Kizer, “Drip Irrigation System”, Oklahoma

Cooperative Extension Fact Sheets available online at

at: http://www.osuextra.com

[4] PSoC® Mixed-Signal Array Technical Reference

Manual (TRM Document No. 001-14463) available

online at: www.cypress.com

 

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