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Minor Project Report

On

“DIGITAL SOIL MOISTURE TEST”
In partial fulfillment of requirements for the degree of
Bachelor of Technology
In
Electrical Engineering

Guided by
Prof. VINEET MEHTA

Name of the student:
BHOMARAM BHISNOI
(10EJIEEOO6)
JAGDEV(10EJIEE022)

DEPARTMENT OF ELECTRICAL ENGG. JIET JODHPUR(MOGRA) 2013

CERTIFICATE

This is to certify that the Minor project entitled“DIGITAL SOIL MOISTER TESTER of Technology in Electrical Engineering of Jodhpur Institute of Engineering & Technology,Jodhpur is a record of the major project work carried out by the following” beig submitted for the partial fulfillment of the requirement of the Degree of Bachelor student:

BHOMARAM & JAGDEV

(III YEAR B.TECH.,VI SEM)

Guide by:-

Head of the Department
Prof. Kusum Agarwal

Prof.Vineet Mehta (Head,EE dept.)

DATE:08-04-2013

Place:-Jodhpur
Abstract:

INDEX

Chapter 1:-Introduction
Chapter 2:-Circuit diagram
Chapter 3:-PCB Designing
Chapter 4:-Errors and Precautions
Chapter 5:-Conclusions
Appendix-I Data sheets
Appendix-II Cost sheets

Introduction:

Here is a simple and compact digital soil moisture tester to check whether the soil is dry or wet. It can also be used to check the dryness or wetness of cotton, woolen and woven fabrics.

For indication, the tester (see Fig.1) uses a number of LEDs driven by ubiquitous display driver IC LM3915 (IC1). The display panel shows the relative magnitude of conductance (reciprocal of resistance) between the two test probes when these are inserted in the soil. 

Fig. 1: Digital soil moisture tester|

Fig. 2: Proposed cabinet with probes|
The tester measures the dryness or wetness through soil resistance readings (0 to about 5 kilo-ohms) and indicates in dot mode by sequential lighting of LED1 through LED9. The first LED (LED1) lights up when the conductance is high (resistance is almost nil).

Normally, the soil resistivity varies from 0 to about 5 kilo-ohms. So for calibration, connect a 5-kilo-ohm potmeter between the two probes. Using trimpot VR1, set resistance to zero (minimum). LED1 should glow. Similarly, set resistance to 5 kilo-ohms (maximum). Now, LED9 should glow.

Assemble the circuit on a general-purpose PCB. After construction, enclose the tester (including battery) in a small plastic cabinet as shown in Fig. 2. The probes can be constructed from a pair of new injection needles. The needles should be firmly fixed about 2.5 cm apart on a piece of laminated plastic sheet. Use short length of a flat, twin wire-lead flexible cable for interconnection. After wiring the circuit, power the circuit using switch S1 and adjust zero-set trimpot (VR1) slowly such that LED1 lights up when probes are shorted. The tester is best powered by a compact 9V alkaline battery.   

Circuit Description:
1: Resistor
2:Capacitor
3:IC LM3915
4:LED
5:Battery

Resistor:
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law:

where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. The ratio of the voltage applied across a resistor's terminals to the intensity of current in the circuit is called its resistance, and this can be assumed to be a constant (independent of the voltage)...
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