This document describes an automatic soil color sensing and identification system using an ARM processor and color sensor. The system aims to address drawbacks of conventional soil color measurement using Munsell soil color charts, which can vary based on human perception. The system works by collecting color sensor output in the form of pulse frequencies, counting pulses for a set time period, comparing the frequency to stored reference values corresponding to hue, value and chroma, and displaying the soil color on an LCD screen. The system is intended to provide more accurate and objective soil color readings than visual inspection with charts.

1. Proceedings of 8th
IRF International Conference, 04th
May-2014, Pune, India, ISBN: 978-93-84209-12-4
89
ARM PROCESSOR BASED AUTOMATIC SOIL COLOUR SENSING
AND IDENTIFICATION SYSTEM
1
CHAYALAKSHMI C.L1, 2
SHANKAR, 3
VINAY DODMANI, 4
MALLAPPA, 5
PARTH K
1
Faculty, 2
VIII Semester students, 3,4,5Dept. of Instrumentation Technology, Basaveshwar Engineering College, Bagalkot
Abstract- Measuring soil colour is important parameter for determining various soil properties. Soil colour although being a
secondary parameter, is essential entityfor the personal of the soil sciences. Soil colour is currently measured using a Munsell
soil colour chart through naked eye observations. This paper deals with the automatic sensing, identification and displaying of
soil colour using embedded system with TCS 3200 colour sensor. An ARM processor is used for processing the data from the
sensor and displays the output on the LCD screen. Embedded C language is used for implementing the automatic sensing and
display algorithm. This system is interfaced to computer data base for future reference and analysis.
Index Terms- Munsell soil colour chart, colour sensor (TCS3200), soil colour.
I. INTRODUCTION
Sensors are a means of gathering information directly
from the process; sensors transform the input into
electrical quantities like voltage or current depending
upon the application and need. This work
demonstrates one of the applications of a color sensor,
which is used for sensing various colors of soil. An
automated system is developed for sensing soil color
for Munsell soil color chart.
Soil colors are most conveniently measured by
comparison with a color chart. The Munsell book of
colors includes nine charts and displays 322 different
standard color chips systematically arranged
according to their Munsell notations on cards carried
in a loose leaf notebook. The Munsell notation for
color consists of separate notations for hue, value, and
chroma, which are combined in that order to form the
color designation. The symbol for hue is the letter
abbreviation of the color of the rainbow[R for red, YR
for yellow-red, Y for yellow] proceeded by numbers
from 0 to 10. Within each letter range, the hue
becomes more yellow and less red as the number
increase. The middle of the letter range is at 5; the zero
point coincides with the 10 point of the next redder
hue. The notation for value consists of number from 0,
for absolute black, to 10, for absolute white. Thus a
color of value 5/ is visually midway between absolute
white and absolute black. One of value 6/ is slightly
less dark, 60 percent of the way from black to white,
and midway between values of 5/ and
1.1 Drawbacks of conventional method
In using the color charts, comparison is obtained by
holding the soil sample directly behind the apertures
separating the closest matching color chips. Rarely the
color of the samples is perfectly matched by any color
in the chart. The probability of having a perfect match
is less than one in hundred ie less than 1%. It should
be evident, however, which colors the sample lies
between, and which is the closest match. The principal
difficulties encountered in using the soil color chart
are as follows:
1] Selection of appropriate hue card.
2] Determination of colors those are intermediate
between the hues in the chart.
3] In distinguishing between value and chroma where
chromas are strong.
In addition, the chart does not include some extreme
dark, strong colors occasionally encountered in moist
soils. This conventional technique is prone to error.
As the readings are based purelyon the naked eye view
the perception may vary from person to person which
in turn reduces the accuracy in measuring the soil
color. Currently there is no device which can directly
determine the color of soil.
1.2 Soil Colour Chart:
Munsell soil color chart is a copyrighted color chart,
which is used for measuring soil color. The color chart
is a book of several pages where each page is a loose
bound book. The present technique used is to compare
the soil color with the colors present in the Munsell
soil color chart and to determine the values of ‘hue’,
‘chroma’ and ‘value’. Soil colors are most
conveniently measured by comparison with a color
chart. The Munsell book of colors includes nine charts
and displays 322 different standard color chips
systematically arranged according to their Munsell
notations on cards carried in a loose leaf notebook.
The arrangement is by the three dimensions that
combine to describe all colors and are known in the

2. ARM Processor Based Automatic Soil Colour Sensing and Identification System
Proceedings of 8th
IRF International Conference, 04th
May-2014, Pune, India, ISBN: 978-93-84209-12-4
90
Munsell system as Hue, Value and Chroma.
The Hue notation of a color indicates its relation to red,
yellow, green, blue and purple; the value notation
indicates its lightness; and the chroma notation
indicates its strength (or departure from a neutral of
the same lightness). chroma notation is indicated by
the horizontal axis in the chart. The value is indicated
by the vertical axis. And the hue notation is present in
the top rght hand side of the leaf.
The colors displayed on the individual soil color charts
are of constant hue, designated by a symbol in the
upper right hand corner of the card. Vertically, the
colors become successively lighter from the bottom of
the card to the top in visually equal steps; their value
increases. Horizontally they increase in chroma from
left to right.
The value notation of each chip is indicated by the
vertical scale in the far left column of the chart. The
chroma notation is indicated by the horizontal scale
across the bottom of the chart. [1]
II. COLOUR SENSING SYSTEM
A color sensor senses the color of soil and converts it
into frequencyoutput. The output of the color sensor is
compared with the standard values which are stored in
the memory of ARM processor and the values are
taken with Munsell soil color chart as reference,
depending upon the value of colour displayed on the
display device. The working methodology explained
with respect to Fig-1 [2].
2.1 Color sensor:
A color sensor is basically a combination of a
photodiode and Current to Frequency converter as
shown in Fig-2.
As the intensity of light falling on the photodiode
varies, the output of the photodiode changes. Current
of the photo diode also varies as the intensity changes
with respect to color.
The color sensor has current to frequency converter
which converts current output of sensor to change in
frequency. The pictorial representation of colour
sensor is shown in Figure-3 [3].
Features of colour sensor:
 High-Resolution Conversion of light
Intensity to Frequency
 Programmable Color and Full-Scale Output
Frequency
 Communicates Directly With a Microcontroller
 Single-Supply Operation (2.7 V to 5.5 V)
 Power down Feature
 Nonlinearity Error Typically 0.2% at 50 kHz
 Stable 200 ppm/°C Temperature Coefficient
 Low-Profile Lead (Pb) Free and RoHS
2.2 ARM LPC2129:
ARM is an advanced RISC machine with less number
of instruction sets. The ARM processor is the
advancement in the microcontroller family with
enhanced computational ability and performance. The
key philosophy behind the ARM design is simplicity.
The ARM7 is a RISC computer with a small gate
count. This makes it ideal for embedded systems. It
has high performance, low power consumption and it
takes a small amount of the available silicon die area
[4][5].
Features of the ARM LPC2129:
 32 bit RISC processor, with high code density
and available with hardware debugtechnology.
Load store architecture.
cycle execution for certain instructions.
Inline barrel shifter.
Thumb 16 bit instruction set.

3. ARM Processor Based Automatic Soil Colour Sensing and Identification System
Proceedings of 8th
IRF International Conference, 04th
May-2014, Pune, India, ISBN: 978-93-84209-12-4
91
 Conditional execution
 Enhanced Instructions: DSP
 Orthogonal instruction Set
 Large 16 x 32 register file.
 Fixed op code width of 32 bits to ease decoding
and pipelining.
 Powerful indexed addressing modes.
 Simple, but fast, 2-priority-level interrupts
subsystem with switched register banks.
2.3 LCD
A 16 × 2 line LCD is used to display the colour of the
soil. LCD requires less power, provides backlight
during lowlight vision. LCD is interfaced with a
microcontroller in byte mode (8-bits of command/data
are transmitted at a time). The data lines D0-D7 of
LCD are connected to P1.0 to P1.7 (P1) and control
lines RS (Register select) and E (Enable) are
connected to P3.4, P2.7 port pins of LPC2129
respectively.
III. DESIGN AND IMPLEMENTATION
The following are the steps for identifying the
frequency of the incoming pulses from the colour
sensor.
 The sensor is placed inside an enclosed block.
Such that the box has a single opening for the soil
sample insertion.
 The sensor gives output in the form of pulses
which are fed as the input to the ARM processor.
 The number of pulses is counted for a pre
determined time period for 10 sec.
 For example consider the frequency of a certain
colour as 3 kHz, the equivalent count for 10 seconds is
calculated as follows
Time period = 1/frequency
Time period = 1/3 k = 0.33 msec
Pulse Count for 10 sec = 10000 m =
0.33m
Decimal code = 30303.0303
Equivalent HEX code = (765F)h
 Referring the hex number colour can be
identified.
Following are a few colours with their frequency and
respective equivalent hue, value, and chroma
notations.
Table 1.1: Various soil colours with their Hue, value and chroma
3.1 Experimental setup of system:
The system is implemented in the laboratory to display
the colour of the soil and subsequent value, hue, and
chroma as V, H and C respectively. The entire set up is
shown in photo snaps as shown in Figure-4 and 5. The
program is developed as per the flow chart shown in
Figure-6.
These values could be used in generation of data base
pertaining to a specific area for the soil characteristic
analysis by the agricultural authorities or for
researchers.

4. ARM Processor Based Automatic Soil Colour Sensing and Identification System
Proceedings of 8th
IRF International Conference, 04th
May-2014, Pune, India, ISBN: 978-93-84209-12-4
92
Figure- 6: Software flow chart
CONCLUSION
A colour sensor when interfaced with suitable
circuitry can sense and display various colours of soil
samples present on the surface of the earth, with the
reference of the Munsell soil colour chart. This paper
presents a design and implementation of a handy tool
for the professionals of the soil sciences to undermine
the soil colour with unmatched accuracy, which
eliminates the factor of human error. As soil colour is
a basic parameter, with knowledge of this parameter
further research can be done on the soil and steps for
betterment of the soil quality can be found.
REFERENCES
[1] http://www.munsell.com
[2] http://www.philips.com/lpc 2119_2129
[3] TAOS-Texas advanced optoelectronic solutions.
[4] http://www.ams.com/eng/products/light-sensors/color-sensor
[5] The insider’s guide to the PHILIPS ARM7-based
microcontrollers- Trevor Martin
[6] http://www.hitex.co.uk/arm
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