SENSOR SYSTEM USING INTERNET COMMUNICATION

Measuring via Internet

Miroslav Husak

Department of Microelectronics, Czech Technical University in Prague,

Technicka 2, CZ-166 27 Prague 6, Czech Republic

Keywords: Sensor, Measurement, Internet, Data communications.

Abstract: The paper describes a sensor system for measurement and transfer of data via internet. Sensor data are

measured at different locations. The concept of read up sensor data, data transfer and data display is

presented in the paper. The realized system for measurement of air temperature, pressure and humidity is

described. Hardware and software of the measuring device have been realized. Eight physical quantities can

be measured by basic sensor system. The system consists of 16 configurations input/output for sensor

connection. Additionally, sensors can be used by the support of software widespread. RS-232 interface has

been used for its simplicity. Ethernet interface can be used by the converter. The control software of the

whole system has been designed. There are many program functions implemented. The design has been

were verified by the realized system sample. All implemented functions can be displayed on WEB pages.

Common software equipment can be used to view the web pages (PDA or mobile phone).

1 INTRODUCTION

The paper describes design and implementation of a

system solving transfer of measured sensor data via

the Internet. A web page has been created on an

Internet server where information is stored,

processed, and displayed. The system is divided into

four basic function blocs and each bloc can be used

at a different location.

Measuring equipment. Measuring equipment

acquires the data from the sensors, e.g. temperature,

pressure or humidity. The device consists from the

hardware and software for handling the sensors and

sending the measured data to the computer. The

measuring equipment is able to be active without

external power supply for certain time period.

Measured data are stored into the internal memory

and later sent to the computer.

Program for reading. The program is determined

for reading the data and saving them into the

computer. If the measuring equipment is connected

to the computer the program is able to read the saved

data from the internal memory of the device. The

program sets up the measuring equipment for correct

addressing the data from the sensors, i.e. where to

store the data from which sensor. The configuration

of the measuring equipment determines the number

of the active sensors, the position of the inputs and

other properties. The measuring equipment is

connected to the computer through corresponding

interface, e.g. serial port. It is essential to ensure

sufficient memory of the computer for saving the

measured data. Successive distribution of the

measured data is realized using the Internet

connection.

Software for data transfer. This software

cooperates with the presentation layer and it is

running on the same computer or server as the

program for reading. The software is reading the

data which have been stored by the program for

reading; it is modifying them and consequently

storing them into the database. If the data are not

stored on the same computer as the software for data

transfer is running on, the data must be in the same

format. The software can run on the Linux as well as

on the MS Windows platforms.

Presentation layer. This part is used for

generating dynamic web pages. The web pages

combine the text information and the graphical

curves which are representing the measured data or

some previously recorded data. The presentation

layer consists of the set of the PHP scripts. The

scripts are changing the server configuration,

specifying the way of the data presentation, loading

304

Husak M. (2006).

SENSOR SYSTEM USING INTERNET COMMUNICATION - Measuring via Internet.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 304-309

 SciTePress

the data from the database, changing the data,

computing the statistics from the measured data,

creating the graphical characteristics, etc.

Measuring

device

Sensor

INTERNET

Sensor

Read up

Data transfer

software

WEB page

presentation

Figure 1: The simplest configuration of the measuring

system.

Web pages are generated by the web server and

MySQL database server. These applications can be

run on the several kinds of the operating systems.

The simplest configuration of the system is shown in

Figure 1. All software is running on the one

computer, which is connected with the sensors.

Measuring

device

INTERNET

Measuring place B

π Read up

π Data transfer software

π WEB page presentation B

Measuring

device

Measuring place A

π Read up

WEB pages presentation A+B

π Data transfer software

π WEB page presentation A

π WEB page presentation B

Figure 2: System measuring at different locations.

The system configuration for measuring the data

at different locations is illustrated in Figure 2. The

system has one presentation layer, which is common

for all other parts. Each measuring point can differ

in the hardware and software equipment. This

difference is caused by different demands laid on the

measuring function of each part of the system.

2 DESIGN OF MEASUREMENT

INSTRUMENTATION

HARDWARE

A measurement equipment enabling connection of

sensors has been designed. The sensors are aimed at

measuring various physical quantities. Both

analogue and advanced digital-output sensors can be

used. The sensors are designed as single-chip

combinations with signal-processing circuits. The

sensors can be connected directly to a

microprocessor. The microprocessor takes care of

the communication with multiple peripheral

instruments. The analogue-output sensors are

connected to the microprocessor via an A/D

converter. The connection to the PC is through a RS-

232 interface. A logic level converter matches the

microprocessor signal to the RS-232 voltage levels.

A character display has been selected for displaying

the data to the operator.

2.1 Microprocessor and its

Supporting Circuits

An ATMEL 89S9252 type has been selected as the

control processor. The clock frequency generator

circuit has been selected with an 11.0592 MHz

crystal. The crystal frequency selected is suitable for

accurate setting of serial communication speed. In

order to prevent undefined states from appearing on

switch-on conditions, the processor start is delayed.

The delay can be set by connecting a RC network to

the reset input of the processor – see Figure 3.

Figure 3: Reset circuit of the processor.

After the 5 V V

supply voltage is applied, a

logical zero appears at the RST input (defined as V

= 0 ... 3.5 V). The run-up time to the logical zero can

be calculated as

RCt ln⋅=

(1)

where V

= 5 V and V

= 3.5 V. The processor

supports a connection of external memory to the

input/output ports P0 and P1. When no memory is

connected, these ports must be voltage-treated

properly.

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2.2 Connection of Sensors

Digital-output sensors are connected via an AD

converter – see Figure 4. The sensors are connected

to inputs marked as D0 to D6. Analogue output

sensors can be connected through an AD converter.

For the required applications, an 11-bit converter is

sufficient. A MCP3208 type has been selected. It is a

12-bit successive-approximation AD converter. The

converter has 8 inputs (programmable as 4 pseudo-

differential inputs or as 8 independent inputs). The

converter communicates through a four-wire serial

bus, compatible with the SPI protocol. Conversion

speed is up to 10

samples per second.

Figure 4: Connection of digital sensors to the processor

through a multiplexer.

2.3 Output Circuits and Power

Supply

The RS-232 interface is used for PC connection,

because RS-232 implementation is very simple

(having preference over USB). The interface is

connected to UART of the

Figure 5: Circuit connection of serial bus.

processor. The converter MAX232 is used for

change of logical levels – Figure 5. The switch

power supply is used in circuit powered – Figure 6.

The MC34063A is used (ON Semiconductor).

Figure 6: The circuit connection of power supply.

2.4 Used Sensors

The SMT160-30 sensor can be used for the

measurement of temperature (

SMARTEC). The

sensor is 3-pin integrated Si sensor. The output

signal has the form of mark-space ratio. The signal

can be connected to a multiplexer. The mark-space

ratio must be measured and converted using a

counter.

The SHT11T integrated sensor can be used for

the measurement of humidity or temperature

(

Sensirion). The output signal is in digital form. The

sensor is connected to a 2-wire digital bus (signal

clock SCK and a data bidirectional signal DATA).

The output signal as function of humidity is

nonlinear. The temperature compensation must be

applied.

The MPX4115A sensor is used for pressure

measurement (Freescale). A circuit is integrated one-

chip Si sensor of absolute pressure. The sensor has

signal processing on chip together with pressure

measurement and temperature compensation. The

output signal has analogue form in the range of 0.2

V to 4.8 V (range of pressure is from 15 kPa to 115

kPa). The sensitivity in the pressure range is

46mV/kPa. The pressure resolution is 0.045 kPa.

3 SOFTWARE OF

MEASUREMENT

INSTRUMENTATION

HARDWARE

The control program is divided to different

functions. Individual functions control behaviour of

the corresponding instrumentation parts. The

program for communication with AD converter is

simple implementation of the SPI protocol. Another

function performs data read-up and saving from/to

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the EEPROM inner memory of the processor.

Another function controls character LCD display. 8-

wire bus is used for data transfer. Further function

performs data transfer using serial bus and

communication with the SHT11 sensor.

3.1 Program Operation

After initialization the program runs in the infinity

loop. The PC instructions are loaded form the

computer in the loop. Individual functions might be

called from these instructions. All functions are

periodically running in the PC interruption.

a) Device

initialization. The program starts from the

processor memory after power supply switch on.

The output ports of the processor are set up to the

initial state. The timer parameters are set up for

interruption generation. The counter is set up to the

speed of 9600 baude per second. The Watchdog

circuit is triggered. The configuration information is

read from the EEPROM memory of the processor.

The configuration information contains:

• Number of connected sensors (1-8)

• Interval of data record to inner memory - when

data are not processed in the PC

• EEPROM dimension of processor

• Frequency of measurement (frequency is

determined by frequency of interruption calls)

• Configuration bytes of individual sensors

b) Interruption timer service. The interruption

service provides: reading the data, data processing,

data displayed and data transmission to the PC –

Figure 7.

The program uses three counters in that

interruption. The counters are saved in the global

variables. The global variables are saved during

individual calls of the interruptions. The counters

are:

• Counter with number of currently active sensor

• Counter for providing averaging number

• Counter for providing number of measured

characteristics to be saved in the memory

The program decides by the two latter counters to

ramify – Figure 7. Basic functions are displayed in

the flow diagram.

Reading data from sensors. The sensor counter

decides which sensor to use. The program reads data

from that sensor.

Value calculation. Value calculation is performed

after averaging cycle. Value output is periodical

after each calculation.

Value display. Values are displayed and sent to

the PC. The information contains sensor number,

sensor type, measured value and quantity.

Figure 7: Interruption service.

c) Instruction reception. The program reads the

instructions from the PC in the program loop. The

functions are called by these instructions. The

functions execute these instructions. The instructions

are represented only by a single character (for

simplicity).

d) Function callable from computer. The

configuration function is defined for the device

configuration. The function is very simple, it

overwrites fifty configuration bytes by new data.

Automatic processor restart is performed after

reading the new configuration.

4 DATA READING AND

TRANSFER SOFTWARE

The software performs data reading from the

measuring device. Then it performs data transfer via

internet to the web server– Figure 8. The software is

divided into two parts. The first part executes data

reading from the measuring device. That software

part is running always on the PC connected with the

measuring device. The second software part formats

data for the web pages. The software supporting the

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web pages is written in the PHP language (PHP:

Hypertext Preprocessor)..

Figure 8: Read up and transfer via internet software

4.1 Software Support of Measuring

Device Control

a) Configuration File.

The configuration file sets up the PC. It defines

location for saving read values; it contains setup

information for connecting the device. Setup

information contains:

• Setup of serial port number connection

• Measuring frequency of the device

• Interval of data record in device

• Memory size of the device processor

• Setup of individual sensors

Individual sensors have in the setup items:

• Sensor data directory for saving

• Sensor type

• Specific sensor setup (input position)

• Corrective constants

b) Program operation.

Initialization. After start the script performs several

operations (setup of infinite time limit for script

running, setup of start up limit of one script

installation, PHP process identifier is saved to the

file). The next step is reading the configuration file.

Data reading. The script starts reading data from the

measuring device using serial bus.

Data processing and saving. Sensor data are sent

to the PC. Data are processed in the PC (more

precise calculation). The output values are corrected

by setup constants. Final values are checked (a

presence in the defined interval).

Virtual sensor. Special properties can be set up in

the program. It is possible to have a sensor that is

not in the measuring device in reality. The sensor

value is calculated as a mathematic operation.

4.2 Software Support of Data

Transfer via Internet

This part of software performs data saving to a

database. The data are acquired from the measuring

device. The transfer and saving of data is realized

using a PHP script. Since the script uses database

access, it is necessary to install support for the

MySQL database. Another extension is represented

by CURL that provides comfortable access to data

via internet.

Setup. The setup contains „data series“. Data of

individual sensors build up the data series.

Individual series are defined by the configuration

files.

Data copy. The source path, the target path, and

the filename are necessary information for creation

of a data copy. The data are saved in several files.

The interval of copying is set up to three minutes.

Database format. SQL database (Structured

Query Language) is suitable for data saving and

their use on the web pages. Using SQL queries

allows very simple reading of data according to the

requested parameters.

The database structure is very simple. Data series

corresponds to the measured sensor value with

assigned time value (the first column contains time,

the second column contains measured value). The

measured data are changing very slowly. The data

are saved to the database only in the case of change

(the result is acceleration of data operation). That

limits the calculation of various statistic

characteristics (data absence in time). Therefore

additional column is inserted to the structure. The

duration of a certain value is saved in this column.

The format „Unix Timestamp“ is used for saving

time information. Time values are represented by

32-bit number. PHP script converts that format.

Other two matrices have been designed (they save

time and space for data processing). The matrices

contain partially preprocessed data, namely average

values, minima, and maxima. The matrices serve for

using data from a longer time interval.

Data saving. Data are read from data series in the

files. Data are transformed to correct format and

saved to the database. Data are not saved as a single

series. One single SQL query is created. All new

data are saved in batch mode. Operation speed is

higher in that case.

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5 WEB PAGES AND RESULTS

The basic requirements have been defined for the

design of the web pages: Simple layout and well-

arranged design, text display of current measure

values, current measured characteristics within day,

measured characteristics and text outputs for

arbitrary data interval.

The page layout is shown in Figure 9. Very large

number of operation is necessary for display of one

web page. Individual files control different attributes

of the web page, for example: web page layout, data

preparation from database, access interface to

database records, conversion of common call

database function to concrete instruction, reading

concrete database record, reading web page setup,

probing extreme values.

Figure 9: Web page layout.

The main file controls a skeleton of the page.

Current values are displayed in current day.

Additional information of extreme values is added

to the pictures.

Page “history” allows to visualize the information

in different way, for example: One picture with

characteristics in the concrete time interval, table

with minimum, average, maximum values for

concrete days, months, years, table with minimum,

average, maximum value through current day.

Another file performs generation of all pictures.

Pictures can be saved to the database. Different

parameters of pictures can be set up: File name,

Displayed time interval, Picture dimensions, Picture

captions, Axis ranges.

6 CONCLUSIONS

Hardware and software of measuring device have

been realized. The basic system measures eight

physical quantities. In the paper, the system for

measurement of air temperature, pressure and

humidity is described. Measured data are transfered

via internet.

Measuring device. The system consists of 16

configurable inputs/outputs for sensor connection.

Five sensor types have been designed for the system.

Eight measuring devices can be used in the system.

Additional sensors can be used – the extension is

software supported. The RS-232 interface has been

used due to simplicity of connection. Ethernet

interface can be used for the converter.

Software equipment. Control software of the whole

system has been designed. Many program functions

constitute the whole software. Individual functions

perform individual operations of the system. The

design has been verified by a realized system

sample. All functions can be displayed on the web

pages. Common software equipment can be used for

viewing the web pages (PDA or mobile phone).

ACKNOWLEDGEMENTS

This research has been supported by the Czech

Science Foundation project No. 102/06/1624 “Micro

and Nano Sensor Structures and Systems with

Embedded Intelligence” and partially by the

research program No. MSM6840770015 "Research

of Methods and Systems for Measurement of

Physical Quantities and Measured Data Processing "

of the CTU in Prague.

REFERENCES

ON Semiconductor. MC34063A, MC33063A,

NCV33063A: 1.5 A, Step-Up/Down/ Inverting

Switching Regulators December, 2005.

www.onsemi.com

SMARTEC. SMT16030 DIGITAL TEMPERATURE

SENSOR, 2005.www.smartec.nl.

Sensirion. SHT1x / SHT7x Humidity & Temperature

Sensor 2005. www.sensirion.com.

Freescale Semiconductor. MPX4115A, MPXA4115A,

2006. www.freescale.com.

PHP: Hypertext Preprocessor. www.php.net.

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