A low cost solution to monitor environmental [631720]

A low cost solution to monitor environmental
parameters in industrial area perimeters
Nicolae Patrascoiu1
1University of Petrosani, Depar tment of System Control, Computer Science, Electrical an Power
Engineering, 20 Univers itatii, Petrosani, Romania
Abstract. The monitoring of environmental parameters in active industria l
areas where there exist potenti al sources of pollution, and eve n more so in
the area of decommissioned or closure mining activities, is ver y important
from the point of view of prevention of environmental accidents . In this
paper, we propose a solution for the monitoring of the environm ental
parameters with the local acqui sition and processing of the dat a and the
transmission of alarm signals to a higher hierarchical level th rough the use
of radio communications. A flexible hardware structure and soft ware
development concept are presented to be integrated into the nat ional air
quality monitoring network.
1 Introduction
The measurement of parameters of the environment and air qualit y parameters also are
among the most relevant informati on for humans and the other be ings. It is known there are
parameters like temperature, humidity, but also volatile organi c compounds, particulate
matter, or CO2, which are highl y relevant for the health of hum an beings.
The measurement of these parameters can be made by periodicall y collecting air samples
or through a monitoring process which means using data acquisit ion and processing system.
If the parameters are monitored at a long distance from the dat a acquisition points we
have a remote monitoring system. Selecting and using the right equipment for remote
monitoring and control applications can introduce some challeng es to be solved [1], [2].
Selecting and using the right equipment for remote monitoring a nd control applications
can introduce some challenges to be solved.
In recent years, new technologies and products have emerged to address some of these
challenges, but in many cases, th ese products must be selected taking into account:
 the application itself;
 geographic extension of the area where the data is being acquir ed;
 the form in which data will be acquired and processed primarily ;
 how the data, after primary processing, is transmitted to the h igher monitoring level;
 how the data is provided to the user, in order to make a decisi on.
The present remote monitoring methods include a wired method an d radio method to send
the acquired data. The wired method which can involve the troub le in the strength of the
connection, the effects of the working environment, the informa tion transmission in time, the
operation cost and so resulting that it is not suitable for the most of such applications [3], [4].

2. Sensors used to monitor environmental parameters
Sensors used to monitor the quality of environmental factors ca n be classified by
destination as follows:
 used to determine the pollutants that contaminate the environme nt;
 used to determine the components which are naturally composed a n observed
environmental factor;
 used for the determination of natural and climatic factors.
In any of these categories, there may be several types of senso rs that are different from
each other based on their operati ng principle. Thus, based on t heir operating principle, the
sensors can be divided into electrochemical sensors, optical se nsors, biosensors, piezoelectric
and acoustic sensors or electroni c sensors. From the point of v iew of this paper, electronic
sensors are of interest.
Generally speaking, there are many methods of measurement have established using
electronic sensors in the measurement of the environmental para meters and this category
includes catalytic, semiconductor (solid-state), electrochemica l and infrared sensors.
2.1 Catalytic sensors
The catalytic measuring principl e is highly suitable for the de tection of the volatile
organic compounds (VOCs) that’s means combustible gas and vapou rs.
One of the recent techniques int roduced for VOCs detection invo lves passing the sample
of gas over the surface of a sem iconductor material, which is m aintained at a constant
temperature (fig.1.). The adso rption of gas molecules on to the surface of the semiconductor
modifies its electrical conducta nce. The selectivity of the gas to be detected may be achieved
by the choice of semiconductor and the operating temperature. H owever, filters may be
necessary to avoid interference or poisoning from other airborn e pollutants [5].
Fig.1. Catalytic solid-state sensor
The relationship between sensor resistance and the concentratio n of deoxidizing gas can
be expressed by the following equa tion over a cer tain range of gas concentration:
where: RS represent electrical res istance of the sensor, [ C] represent gas concentration, A
represents a sensor cons truction constant and a is the slope of RS curve.
The measurement system uses an e mbedded compute unity for signa l processing and for
sensor calibration also and the most used a compute unity in th is systems is microcontroller
because this integrates as many of the functions as possible in one package.
In general, manufacturers of these types of sensors provide use rs with a graphical
performance feature that can be approximated by exponential or rational functions, like next
relations:
-VH
+V H
heater resistance R H
sensor resistance R S
Power supply +V S
Power supply -VS
a
SRA C ( 1 )

Here, the quantities(1)
SR, (2)
SR represents the sensor resistance values corresponding to
concentrations (1)C[%] and respectively )2(C [%] gas in environmental air and the quantity
Cm represent the arithmetic mean val ue of these concentrations. T hus, is possible by using
only the three probes of gas concentration Ci and based on the experimental measuring the
corresponding RSi values of the sensor resistance it ca be compute the three qua ntities Cm,
(1)
SR and (2)
SRby using the relations (3)
   
    
3322 2 1 22 1 1 32
213 2 322 1
(1) 3331 0 0 3
3322 3 2 (2)
32SS S S
m
SS SS
SS m S
S
m
SS m S S
SCR CR C C CR CR C CCRR C C RR C C
CR CR CRRC
CR CR C R RRCC      
  
   (3)
Using a simple Matlab program it can draw the simplified static characteristic in graphic
form of the methane sensor TGS2611. In the fig.2 is represents a comparison between the
simplified model (a) and the graphics model provided from TGS26 1 1 m e t h a n e s e n s o r
datasheet (b) where R0 is sensor resistance in 5000 ppm (0.5%) of methane.
Fig.2. Simplified model and real model of t he TGS2611 sensor
2.2 Digital sensors
Digital sensors provide digital information to the user with th e benefit of eliminating the
need to use the analog signal filters to eliminate spikes speci fic to such an analog signal.
Unlike the case described above for digital sensors, due to sig nal processing, there is a
possibility of integrating multiple functions into the same har dware structure [6].
The BME680, produced by Bosch Sensortec, is a digital 4-in-1 se nsor which can be used
for gas, humidity, pressure and temperature values measurement based on specific
measurement principles. The sensor module is housed in a compac t package with small
dimensions and low power consumption. These characteristics ena ble the integration in
battery-powered or frequency-coupled devices, such as handsets devices or other
measurement systems. 2ln
)2( )1( )2(
mCC
S S S S e R R R R (2)
C CC R CRR
mS m S
S)2( )1(
(3)
Model provided by
rational equation
Model provided by
exponential equation

This sensor uses specific software (BSEC: Bosch Software Enviro nmental Cluster) which
is built to work with the 4-in-1 integrated sensors inside the BME680. Based on an intelligent
algorithm, the BSEC provides output information. For an indoor environment, this output is
in an index indoor air quality (IAQ) that can have values betwe en 0 and 500 with a resolution
of 1 to indicate or quantify the quality of the air available i n the surrounding. Furthermore,
the BSEC solution supports different operation modes for the ga s sensor to address the
necessary power budget and update rate requirements of the end- application [7].
The sensor provides, for delivery the information to the user, two digital interfaces SPI
(3-wire/4-wire) and I2C, any of which can be selected. The meas urement can be triggered
through a request from the user o r can be performed at regular intervals.
The sensor can be operated in three power mode: sleep mode, nor mal mode, and forced
mode. In sleeping mode, no measurements are performed to keep t h e m i n i m a l p o w e r
consumption. In normal mode, the sensor operation automatic swi tching between the
measurement period and standby period. In forced mode operation the sensor performs a
single measurement on user request and after that switch in sle ep mode until a new user
request. This operation mode is recommended for applications wh ich requires a low sampling
or in applications where is used a user synchronization signal.
2.3. Chemiresistive Sensors
Many VOC measurement techniques have been developed and include t h e r m a l –
conductivity detectors (TCDs), ga s chromatography (GC) detector s, non-dispersive infrared
(NDIR) sensors, and many others.
Current-generation air quality sensors typically use a chemires istor that is a
semiconductor material that varies its resistance in response t o changes in the surrounding
chemical environment. A chemiresistor works through adsorption and desorption, which are
surface processes that involve t he accumulation or release of g as molecules. Adsorption and
desorption vary the free charge carrier concentration in the ma terial, causing the change in
resistance. Both p-type and n-type semiconductors can exhibit c hemiresistance and the used
material are materials metal oxi des (MOx), such as zinc oxide ( ZnO), tin oxide (SnO2),
indium oxide (In2O3), tungsten trioxide (WO3), copper oxide (Cu O), and nickel oxide (NiO).
A MOx sensor makes use a thin-film metal-oxide layer to measure air quality; the sensor
outputs an analog signal that indicates the concentration of th e target gases. This signal is
then converted into a digital equivalent in which specific gase s are quantified. The adsorption
process requires high temperatur es, so the MOx sensor is packag ed with a heating element
as shown in fig.3. [8]
Fig.3. A MOx integrate sensor structure
3. Hardware structure
In this paper, it is considered the case where the processing u nit is an ESP8266 module
to which on I2C bus the digital environmental sensors BME680 ar e connected. Thus, this
processing unit also assures the connection to a wireless netwo rk.
The ESP8266 module is low cost standalone wireless transceiver with full TCP/IP stack
and microcontroller capability tha t can be used for IoT develop ment systems. Ceramic or Silicon substrate include 
electrical contacts and bond padsHeated sensing material chnage 
resistance on presence of target gas
Passing current/voltage through 
resistive heater heats the structure

The ESP8266 can be used as such or can be applied to any microc ontroller design as a
Wi-Fi adaptor through SPI/SDIO or I2C/UART interfaces. Besides the Wi-Fi functionalities,
ESP8266 also integrates an enhanced version of the 32-bit proce ssor and on-chip SRAM. It
can be interfaced with external sensors and other devices throu gh the GPIOs, resulting in low
development cost at the early stage and minimum footprint. ESP8 266 integrates antenna
switches, RF balun, power amplif ier, low-noise receive amplifie r, filters, and power
management modules.
Typically, the ESP8266 is integrated into a development board s o that the user can easily
access the pins to use the featur es provided by it. Typically, the ESP8266 is integrated into a
development board so that the user can easily access the pins t o use the features provided by
it. One of the simplest such development boards is the ESP8266 WeMos D1 mini that also
includes a USB CH340 interface th at allows it to be connected a nd programmed directly from
the computer.
The fig.4.a. shows the functional blocks of ESP8266 and the fig .4.b. shows ESP8266
WeMos D1 development board [9].
Fig.4. The functional bloc ks of ESP8266 and ESP8266 WeMos D1 development board
The I2C bus is a means of connecting several peripheral input a nd output devices that
support I2C on two wires. One of those wires is the DATA line c alled the SDA, and the other
is the CLOCK line called the SCL. The information is sent on th ese two lines through the
I2C communication protocol using the specified DIO lines, or ot her common DIO lines of
the ESP8266 module. I2C can be used to connect up to 127 nodes via a bus that only requires
two data wires, known as SDA (connected to D2 pin) and SCL (con nected to D1 pin).
To test the functionality of the ESP8266-BME680 assembly, acqui sition of
environmental parameters from two different measuring points wa s achieved by using two
BME680 sensors connected to the ESP8266 module via the I2C bus according to the diagram
shown in fig.5.
MASTER
ESP8266+3.3 V D1 D2
SLAVE
BME860VDD SDI SCK VCC
SCL
SDAR1 R2
GND GND
SLAVE
BME860VDD SDI SCKGND
SDO SDO
0x76 adrress 0x77 adrressnot
connected

Fig.5. Hardware structure used for envi ronmental parameters monitorin g
The BME680's default address is 0x76 (which you get when SDO is connected to GND).
If SDO is connected to VDD the ad dress can be forced to 0x77.
To enable communication on I2C bus, pull-up resistors R1 and R2 need to be connected
from the I2C lines to the supply as shown in fig.5. These resis tors pull the line in a logic-high
a.b.

state when it is not driven to the logic-low state by the open- drain interface and the value of
the pull-up resistor is an important design consideration for I 2C systems as an incorrect value
can lead to signal loss [7].
For the pull-up resistances are imposed two requirements. Thus, the pull-up resistor must
limit the current to a level th at does not exceed the maximum d rain current of the output
transistor and also must prevent excessive current consumption when the SCL or SDA signal
is in the logic-low state.
The minimum value Rmin of these resistances is imposed by the maximum sink current on
the lines in the logic-low state of these and which is IOL=3 mA for the standard and fast
operation modes of the bus. For operating with VDD = 3.3 V and considering the minimum
VOL = 0 V for the logic-low state, it results:
3.31.13DD OL
min
OLVV VRkIm A   ( 4 )
For calculating the maximum value of the resistors R1 and R2, i t is assumed that they
t o g e t h e r w i t h t h e e l e c t r i c a l c a p a c i t a n c e C o f t h e S C L a n d S D A l ines will determine the
transition times, or rise time, between the logical states low to high, tLH, and it cannot be less
than I2C standard rise time specifications. It is known that t he response of an RC circuit to
a voltage step of amplitude VDD, starting at time t = 0 is char acterized by a time constant
RC and the voltage wavef orm can be written as:
 1t
RCDD Vt V e
  ( 5 )
Considering that the rise time is defined between the moments tH and tL of obtaining the
corresponding to the logic-low state voltage VIL = 0.5 V and logic-high state voltage VIH =
1.2 V on the SCL and SDA lines, it follows:
ln
lnDD
H
DD IH
DD
L
DD ILVtR CVV
VtR CVV
 ( 6 )
By defining the rise time tLH based on the difference tH – tL from relations (6), it results:

lnHL L H
max
DD IL
DD IHtt tR
VVCVV
  ( 7 )
Choosing the standard I2C bus specifications values of tLH = 150 ns, VIL = 0.5 V, and VIH
= 1.2 V, and assuming a bus capacitance of C=150 pF, we have the maximum of resistance
value Rmax for pull-up resistors:
3.5maxRk ( 8 )
The value of an I2C pull-up resistor must be large enough to re duce unnecessary current
consumption and small enough to produce an acceptable rise time . The calculations above
are helpful in choosing the value range for pull-up resistors, but it is possible to adjust them
based on the SCL and SDA line capacity variations, depending on the application.
4. Software considerations
The ESP WeMOS D1 module is programmable so that the operation o f the environmental
parameter monitoring system is accomplished by programming the acquisition, processing
and wireless transmissi on of the data [10].

The ESP8266 Wemos D1 mini Pro is an Arduino-like board that run s using the ESP8266
microcontroller and th e most important difference to an Arduino module is that the ESP8266
has the wireless capability that means this can b e natively con nected to a Wi -Fi network.
Based on this observation, it is possible to program this modul e using Arduino
development board-specific programming environments. It can be used a text programming
languages such as the familiar Ar duino IDE or vis ual programmin g media such as Visuino.
Figure 6 shows the way to achieve the required programs in thes e two programming
environments.
Fig.6. Examples of programming of envir onmental parameter monitoring.
5. Conclusions
There are many solutions, some in function, to monitor environm ental parameters.
The proposed solution involves ac quisition, processing, and tra nsmitting, which can be
directly into the Internet, of t h e d a t a o b t a i n e d t h r o u g h a s i m p le and especially low-cost
system.
The type of sensors can be expanded provided that the same prot ocol type is used to
include the user in a network.
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