Engineering, 2010, 2, 690-697
doi:10.4236/eng.2010.29089 Published Online September 2010 (http://www.SciRP.org/journal/eng)
Development of Multi-Channel Data Logger for Indoor
Environment
Anuj Kumar, Indu Prakash Singh, Suresh Kumar Sud
Instrument Design Development Centre, Indian Institute of Technology Delhi,
Hauz Khas, India
Received March 12, 2010; revised June 2, 2010; accepted June 16, 2010
Abstract
Environment monitoring has become a necessity because of global warming and climate change. All across
the globe researchers are trying to monitor the environmental parameters of temperature, humidity and pol-
lutants gases mere precisely in real time. Sensing system using sensor arrays has been developed to monitor
indoor environment, however, these systems are costly and have not gained wide acceptance. Precise moni-
toring of building environment has a huge potential in terms of energy savings. In this paper, an effort has
been made to develop a 4-channel energy efficient and low cost data logger for indoor environment. The
Data logger is proposed to be developed with the use of PIC 18F4458. Real Time Clock and EEPROM are
interfaced for sampled data with the instance of sampling time and month/date/year; these sampled data will
be stored in the EEPROM to the note pad tabular form with the help of graphical user interface (GUI).
Keywords: Gas Sensors, GUI, (Real Time Clock) RTC, ADC, Smart Transducer Interface
1. Introduction
Indoor environment and built-architecture are closely
associated. The built environment affects indoor physical
environments, and subsequently health and quality of life
of occupants. There is evidence showing the pathways
and mechanisms by which the built environment affects
health and factor associated with specific aspects of
physical and mental health. The problem has become
acute in recent past because of the rapid industrial grow-
th in last half century and has led to change in lifestyles
(Become more dependent on indoor environment) [1].
The main factors of the environmental condition are the
air quality and environmental parameter of the inside
unconditioned environment. Across the world indoor air
quality monitoring is gaining hotspot in present resear-
ch works because recent study has put forth that 30 –
40% of total natural resources are exploited by the build-
ings and almost 50% of energy resources is used to con-
dition buildings in industrialized countries. The reality is
that indoor air can be up to 10 times more polluted than
outdoor air [2]. The major contaminants of indoor envi-
ronment pollution are CO2, CO, O3, SO2 and NO2. Many
researchers are collect the data for different techniques,
in different fields are facing similar difficulty in data
collection i.e. , needs a user friendly system is able to
collect data from the work place and buildings environ-
ment. Pardo et al. developed a gas measurement system
based on the IEEE 1451.2 standard. They have used the
4-gas sensors (tin oxide), 1-temperature and 1-humidity
sensor; this prototype system will be work as electronic
nose [3]. Camara et al. developed a STIM (smart trans-
ducer interface module) based on the IEEE 1451 stan-
dard. This prototype system will be work with a lot of
different transducers without the necessity of change of
the control hardware and software [4].
Available technologies for sensing these environmen-
tal parameters are developed by Onseat HOBO, Spec-
trum Technologies (Watch Dog weather conditions),
TandD, Telaire (Wireless Monitoring Systems), Testo,
Log Tag, Measurement Computing Corporation, Mon-
arch Instruments, MSR Electronics GmbH, P3 Interna-
tional, Quality Thermistor, S3 Crop, Sensaphone, Sansa-
tronics, Lascar, ICP, Graphtech, Extech Instruments,
Dickson, Dent Instruments, Davis, ACR System Inc, 3M
International, and Acumen [5].
But we found the developed system is not suitable for
the real time monitoring of the indoor environment and

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will be required to store the information and data collec-
tion for the long duration.
To focus on this problem we are trying to develop a
low cost and energy efficient multi channel data logger
for indoor environment. We face only 4-parameter such
as temperature, relative humidity, SO2, and NO2. It can
be summarized as follows-interface of LCD (to display
the output of various modules), RTC and EEPROM with
microcontroller and interface of the data logger to the
personal computer by using the serial (RS-232) port,
minimization of power consumption in order to enhance
battery life and preparing the user friendly graphical user
interface in visual language to operate the data logger.
2. Sensors
A sensor is a device that measures a physical quantity
and converts it into an equivalent analog or digital signal
which can be read by an observer or by an instrument.
Monitoring of an indoor environment involves sensing
the changes occurring inside it. The parameters which
are of importance are the temperature, relative humidity,
and concentration level of air pollutant SO2, and NO2
inside the building [6,7]. In this paper we have used a p
type or n type resistive based semiconductor gas sensor.
A gas sensor detects particular gas molecules and pro-
duces an electrical signal whose magnitude is propor-
tional to the concentration of the gas [8]. No single type
of gas sensor is 100% selective to a single gas. A good
sensor is sensitive to the measured quantity but less sen-
sitive to other quantities. Available gas sensors are based
on five basic principles. These can be electrochemical,
infrared, catalytic bead, photo ionization and solid-state
[9,10]. We have selected these sensors because they
produce a strong signal for the selected variable espe-
cially at high gas concentrations with adequate sensitiv-
ity. They have a fast response time, high stability, long
life, low cost, low dependency on humidity, low power
consumption, and compact size [8]. Table 1 represents
the Specifications of the Sensors Used in the Multi-
Channel Data Logging System and Table 2 represents
the measurement range of the developed system.
3. Signal Processing of the Sensors
Four sensors along with their signal conditioning circuit
are used to sense the desired parameter. One is tempera-
ture, second is humidity, third is SO2, and fourth is NO2.
Signal conditioning circuit for that sensor needs to be
connected externally. In software we can select any of
the analog channel and hence the sensor. Interfacing of
temperature, humidity, SO2, and NO2 sensor with micro-
controller PIC 18F4458 is as follows.
Table 1. Specifications of the sensors used in the multi-
channel data logging system [8-10].
Sl.
No.
Sensor
Name/
Manufac-
turer Range Sensitivity
Re-
sponse
Time
1.
LM35CZ
Precision
Temp. sensor
National
semicon-
ductor,
USA
−40 to
110°C 10 mV/°C < 2 sec
2.
HIH–4000
Humidity
sensor
Honeywell,
USA
0 to
100% 0.60 pF/%RH15 sec
3. SO2-BF Alphasense,
UK
0 to
100
ppm
300 to 440
nA/ppm (20
ppm SO2)
< 30
sec
4. NO2-A1 Alphasense,
UK
0 to 20
ppm
−400 to −750
nA/ppm
(10ppm NO2)
< 40
sec
Table 2. Represents the measurement range of the develop-
ed system.
Sl. No.Measured Minimum Range Maximum Range
1. Temperature 0°C 70°C
2. Relative Humidity0% 100%
3. SO2 0 ppm 3 ppm
4. NO2 0 ppm 2.5 ppm
3.1. Temperature Sensor
National semiconductor’s LM 35 IC has been used for
sensing the temperature. It is an integrated circuit sensor
that can be used to measure temperature with an electri-
cal output proportional to the temperature (in °C). The
temperature can be measured more accurately with it
than using a thermistor. The operating circuit of tem-
perature sensor is shown in Figure 1. The output voltage
of LM 35 is converted to temperature in °C is [10] as
shown in Equation (1).


.(C)100/ 7C
out
Temp V  (1)
VOUT = output voltage of the sensor (volts)
Figure 1. Operating circuit of temperature sensor (LM35 CZ).

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3.2. Humidity Sensor
The sensor circuit develops a linear voltage vs. RH out-
put that is ratio metric to the supply voltage. That is,
when the supply voltage varies, the sensor output voltage
follows in the same proportion. It can operate over a
supply voltage range between 4.0 V to 5.8 V. At 5 V
supply voltage (at room temperature) i.e., the output vol-
tage ranges from 0.8 to 3.9 V as the humidity varies from
0% to 100% (non-condensing). The humidity sensor
functions with a resolution of up to 0.5% of relative hu-
midity (RH), with a typical current draw of only 200 μA,
the HIH-4000 series is ideally suited for low drain, bat-
tery operated systems. The pin configuration of humidity
sensor is shown in Figure 2. The change in the RH of the
surroundings causes an equivalent change in the voltage
output. The output is an analog voltage proportional to
the supply voltage. Consequently, converting it to rela-
tive humidity (RH) requires that both the supply and
sensor output voltages (At 25°C) [10] as shown in Equa-
tion (2).




/0.16/ 0.0062
out supply
RHVV (2)
RH = Relative humidity (%); Vsupply = Input voltage
3.3. Operating Circuit of the SO2 and NO2
Sensor
The SO2 and NO2 sensor operating circuit is shown in
Figure 3. In general the output of the IC1 is connected to
the microcontroller pin AN2 and AN1 respectively [9].
4. Analog to Digital Conversion and
Interfacing of LCD with Microcontroller
We are using the on chip analog to digital converter
which is on the microcontroller PIC 18F4458. This ana-
log to digital converter is having the 12 bit resolution
with programmable acquisition time. It is sensing the
analog signal from the sensor at the variable sampling
rate (1 sec - 1 hour), the sensed value is converted to its
digital equivalent. This digital value is displayed on the
LCD (liquid crystal display) which is interfaced to the
microcontroller [11-18]. Circuit diagram of LCD inter-
facing to the microcontroller is shown Figure 6.
5. Interfacing of Real Time Clock with
Microcontroller
The DS1307 operates as a slave device on the I2C bus.
Access is obtained by implementing a START condition
and providing a device identification code followed by a
register addresses. Subsequent registers can be accessed
sequentially until a STOP condition is executed. When
VCC falls below 1.25 VBAT, the device terminates an ac-
cess in progress and resets the device address counter.
Figure 2. Operating circuit of humidity sensor (HIH4000).
Figure 3. Operating circuit of the SO2 and NO2 gas sensor [9].

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Inputs to the device will not be recognized at this time to
prevent erroneous data from being written to the device
from an out of tolerance system. When VCC falls below
VBAT, the device switches into a low-current battery-
backup mode. Upon power-up, the device switches from
battery to VCC when VCC is greater than VBAT +0.2 V and
recognizes inputs when VCC is greater than 1.25 VBAT.
Figure 6 shows the interfacing of real time clock (RTC).
We are using the DS1307 real time clock which is hav-
ing the following features - real time clock counts Hours,
Minutes, Seconds, of the Month, Day, Year with Leap-
Year Compensation valid up to 2100, 56-Byte, Battery-
Backed, Nonvolatile (NV) RAM for data storage, I2C
serial interface, programmable square-wave output signal,
automatic power fail detect and switch circuitry, con-
sumes less than 500 nA in battery-backup mode oscilla-
tor running, and temperature range −40°C to +85°C
[14,15].
6. Interfacing of EEPROM with
Microcontroller
The EEPROM will store the digital value which is com-
ing from analog to digital converter. We will require the
52.73 MB of EEPROM if we are sampling all analog
channels at the rate of 1 sample/Second. We are using
the EEPROM AT24C256 of ATMEL. This will store the
sample data at different instants. This EEPROM having
the following features - low voltage and standard voltage
operation 5.0 (VCC = 4.5 V to 5.5 V), 2.7 (VCC = 2.7 V to
5.5 V), and 1.8 (VCC = 1.8 V to 5.5 V); 1 MHZ (5 V),
400 KHZ (2.7 V) and 100 KHZ (1.8 V) compatibility,
and 64-Byte page write mode [15,17,18]. Figure 6
shows the interfacing of EEPROM. We are using the I2C
to interface the real time clock (RTC) and EEPROM to
the microcontroller. The IC bus is the most popular of
the 3 serial EEPROM protocols. Figure 6 shows the typ-
ical pin out of an I2C device, showing pins 1-3 as address
pins A0, A1 and A2. Pin 4 is VSS, or ground. Pin 5 is
SDA, the data line. Pin 6 is SCL, the clock signal. Pin 7
is write protect, and pin 8 is voltage, or VCC. Finally,
many I2C chips include address pins as an easy way to
have multiple chips on a single bus while still only using
two connections to the microcontroller [14].
7. PC Interfacing with Microcontroller
Using RS232 Serial Communication
Personal computer is interfaced with PIC 18F4458 using
MAX232. It is the IC used to convert the TTL logic level
to the RS232 logic level. RS232 is the serial communica-
tion protocol that does not require the clock along with
data lines. Two data lines are there one is TX and another
is RX for serial communication. MAX432 has two re-
ceivers (converts RS-232 logic level to TTL logic) and
two drivers (converts TTL logic to RS232 level). Fol-
lowing Figure 6 shows the hardware interface of PIC
with personal computer. Separate power supply has been
provided because minimum power supply needed is 5 V
and MAX232 consumes a lot of current for operation.
External capacitors are required for internal voltage push
to convert TTL logic level to RS232 level. For battery
operated application MAX232 can be used as level con-
verter instead of MAX232, it is low power consumption
logic converter IC for RS232. It is pin compatible with
MAX232 [14].
8. Graphical User Interface
A program interfaced that takes advantage of the com-
puter graphics capabilities to make the program easier to
use. In this paper, the GUI is one of the important parts it
displays the data from microcontroller for data monitor-
ing and analysis. However, the main objective is to dis-
play data received in graphical form. As a transducer
detects and translate an analog signal, the data will go
through a conversion at the ADC and become a digital
format. This digital data is converted in a 12 bit data.
This data will be stored to the EEPROM chip with the
help of Visual Basic 6.0 software. Since the data used the
serial RS232 communication, therefore an initialization
needs to be done which are the baud rate, data bits, parity,
stop bit and the COM port at the PC. The baud rate is the
number of signal changes per second or transition speed
between Mark (negative) and Space (positive) which
range from 110 to 19200, data bits is the length of data in
bit which has one least significant bit (LSB) and one
most significant bit (MSB), the parity bit is an optional
bit mainly for bit error checking. It can be odd, even,
none Mark and Space. Stop bit is used to frame up the
data bits and usually combined with the start bit. These
bits are always represented by a negative voltage and can
be 1, 1.5 and 2 stop bits. The commonly used setting to
establish a serial RS232 communication is 9600 baud
rate, none parity, 8 data bits, and 1 stop bit. As this paper
relates with data collection, thus the data obtained from
the microcontroller needs to be collected and saved. This
can be done by using the GUI monitoring system where
it automatically saves the data received in a note pad.
The data being saved is the date and time during the data
collected and data value it self. Figures 4 and 5, repre-
sents the graphical user interface and logged data in file
[17,18].
9. Schematic of the Data Logger
Figure 6 shows, the full schematic diagram of the data
logger for indoor environment. This data logger has four

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embedded sensor module and other four channels are
open to be used for the measurement of other environ-
mental parameters.
10. Software Design of Data Logger
This subsection includes the software design for all the
modules interfaced with PIC 18F4458. It covers com-
plete software design for data logger. The programs have
been written to the environmental parameters and con-
centration level of SO2 and NO2 gases are monitored for
24 hours and save the data of EEPROM corresponding to
the time and date.
10.1. Programming Steps for I2C Interface
I2C is also bi-directional. This is implemented by an
“Acknowledge” system or “ACK” system allows data to
Figure 4. GUI for the data logger.
Figure 5. Representation of the logged data in file.
be sent in one direction to one item on the I2C bus, than,
that item will “ACK” to indicate the data was received.
Normally, the master device controls the clock line, SCL.
This line dictates the timing of all transfers on the I2C
bus. Other devices can manipulate this line, but they can
only force the line low. This action means that item on
the bus cannot deal with more data in to any device.
10.1.1. Writing to a I2C Chip
The function of writing to the EEPROM is shown here as
“Control IN”, which represents putting the EEPROM in
an “input” mode. Since we are only sending data to the
EEPROM, we use the “Control IN” byte. We will use
“Control OUT” later. Figure 7 shows the display of data
saver memory (data writing of the memory).
Next, the EEPROM acknowledges this byte; this is
shown by the “A” after the byte. It is put on the next line
to indicate this is transmitted by the EEPROM. Next the
PIC microcontroller sends the address byte. The address
byte contains the address of the location of the EEPROM;
we want to write data. Since the address is valid the data
is acknowledged by the EEPROM. Finally, we send the
data we want to write. The data is then acknowledged by
the EEPROM. When that finishes, we send a stop condi-
tion to complete the transfer. Remember the “STOP” is
represented as the “T” block on the end. Once the
EEPROM gets the “STOP” condition it will begin writ-
ing to its memory. The write will not occur until it re-
ceives the “STOP” condition.
10.1.2. Reading from an I2C Chip
The transfer will use the “Control IN” byte to load the
address into the EEPROM. This sends data to the
EEPROM which is why we use the “Control IN” byte.
Once the address is loaded, we want to retrieve the data.
So, we send a “Control OUT” byte to indicate to the
EEPROM that we want data from it. The EEPROM will
acknowledge this and then send the data we requested.
When we are done getting data, we send a “NACK” to
tell the EEPROM that we do not want more data. If we
were to send an ACK at this point, we could get the next
byte of data from the EEPROM. Since we only want to
read one byte, we send a “NACK”. This is detailed in the
specifications for the EEPROM. Figure 8 shows the dis-
play of outcome data saver memory (data reading and
save outcome data in note pad form).
10.2. Programming Steps for LCD Interface
10.2.1. LCD Module is Initialization and
Configuration to Work in 4 Bit Module
Set RS = 0 to send command; send 0b0010 to data lines

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Figure 6. Full schematic of the data logger.
Figure 7. Display of data saver memory.
three times with a delay of 2 ms; to send a byte on 4 data
line. Send higher nibble first and give a RE pulse of 100
us at RE. Send a set of instruction one after another with
a delay of 2 ms between each command to configure
various setting as given in instruction set of LCD data-
sheet. Send instruction set again.
Figure 8. Display of outcome data saver memory.
10.2.2. Display a Character
Set RS = 1; send higher nibble at 4 data lines. Send
100uS RE pulse; send lower nibble at data lines. Send
RE pulse; keep track of number of character already dis-

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played on display panel using LCD count up. Go to line
2 or line 1 according to that.
10.3. Programming Steps for Sensor Data
Collection
There are connected four sensors temperature, humidity,
SO2, and NO2. Data is collected by the ADC inbuilt in
PIC. ADC provides 10 bit of data after the conversion is
completed.
10.3.1. Data Collection of Temperature Sensor
Select the analog channel AN0, alignment of bits for
ADRESH and ADRESL, sampling frequency, Vref,
power on the ADC module by setting ADCON0, AD-
CON1 and ADCON2 registers. Start A to D conversion
by setting ADGO bit high and wait till ADIF flag will
not indicate the completion of conversion and copy the
results from ADRESH and ADRESL to variables.
10.3.2. Data Collection of Humidity Sensor
Select the AN3 and set other features of ADC as tem-
perature sensor and after completion of conversion cop-
ies the result in variable.
10.3.3. Data Collection of NO2 and SO2 Sensor
Data collection from the NO2 sensor needs following
actions to be carried out 1) Selecting the analog channel
AN1, sampling frequency, and alignment of bits for
ADRESH and ADRESL, 2) Vref and power on the ADC
module by setting ADCON0, ADCON1 and ADCON2
registers, 3) starting analog to digital conversion by set-
ting ADGO bit high (wait till ADIF flag will not indicate
the completion of conversion), and 4) copy of results
from ADRESH and ADRESL to variables.
Now repeat the same process to collect the SO2 data
on the channel number AN2.
11. Results and Discussion
Sensors module, EEPROM, RTC, and LCD have been
successfully interfaced to the microcontroller. EEPROM
is successfully storing the logged data with time and date
tag. The sensors data is being displayed on LCD module.
A simple GUI has been designed to store a logged data to
a text file, so that it can be analyzed further. The devel-
oped system is lowest cost and energy efficient system.
The power consumption of the developed system is
minimum (< 250 mA).
12. Conclusions
We have developed a low cost, 12 bit resolution data
logger and successfully measured temperature, humidity,
and concentration of SO2 and NO2 gases. The GUI de-
signed gives a lucratively look to the functioning of data
logger. Initial results of the data logger are encouraging
and we are working on to improve the GUI model as
well as the accuracy of data logger.
13. Future Scope
We can improve the data logger by incorporating the
wireless communication in it. There fore, by combining
the term data acquisition and wireless communication, it
becomes wireless data acquisition. This new innovation
technology has become the trend for most industries and
companies around the world to gather information due to
its reliability and outstanding outcome. The advantage of
this technology is that it did not use any physical com-
ponents or wires to transfer the data obtained from sensor
at transmitter side to the receiver side. As a result, an
effective system is developed where it is not only re-
moves all the conventional hardware and replace with a
transceiver modem for data transfer but also a cost effec-
tive system as well. Moreover, the data transmission
range can be extended into longer range depending on
the transceiver modem capability. With this feature, in-
formation from the transducer could be transmitted faster
and acts as an early alert in case of accident or disaster
such as fire, food and earthquake. By modifying the GUI
we can display the waveforms of the data on the com-
puter console where as presently we are logging the data
to the file. We also can incorporate the USB communica-
tion so that we can transfer the data at high data rates.
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