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Design of online interactive DAQ & control system for
embedded real time application.
This paper describes the design and implementation of a wireless sensor network for
greenhouse environment monitoring. The sensor network was deployed in a commercial
geoponic greenhouse that produces lettuces in a tropical environment. The sensor node was
developed using off-the-shelf components and consists of sensors, a micro-controller and a
low-powered Zigbee module. Real- time data enabled the operators to characterize the
operating parameters of the greenhouse and also to respond immediately to any changes in
the controlled- parameters. The sensor network achieved data transmission rates of more
than 70%.
Appropriate environmental conditions are necessary for optimum plant growth, improved
crop yields, and efficient use of water and other resources. Automating the data acquisition
process of the soil conditions and various climatic parameters that govern plant growth
allows information to be collected at high frequency with less labor requirements. The
existing systems employ PC or LCD systems for keeping the user continuously informed of
the conditions inside the greenhouse; but are unaffordable, bulky, difficult to maintain and
less accepted by the technologically unskilled workers.
The objective of this project is to design a simple, easy to install, microcontroller-based
circuit to monitor and record the values of temperature, sunlight of the natural environment
that are continuously modified and controlled in order to optimize them to achieve maximum
plant growth and yield. The controller used is a low power, cost efficient chip manufactured
by ATMEL of on-chip memory It communicates with the various sensor modules in real-timein order to control the light, aeration and drainage process efficiently inside a greenhouse by
actuating a cooler, fogger, dripper and lights respectively according to the necessary
condition of the crops. Here the data can be read through the wireless ZIGBEE. The sensor
network is developed by ZIGBEE. Also, the use of easily available components reduces the
manufacturing and maintenance costs. The design is quite flexible as the software can be
changed any time. It can thus be tailor-made to the specific requirements of the user. This
makes the proposed system to be an economical, portable and a low maintenance solution for
greenhouse applications, especially in rural areas and for small scale agriculturists.
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BLOCK DIAGRAM:
ZIGBEE
TRANSMITTER
ANALOG
TO
DIGITAL
CONVERTER
LDR
ZIGBEE
RECEIVER
LEVEL
CONVERTERPOWER
SUPPLY
PERSONAL
COMPUTER
MICRO
CONTROLLER
TEMPERATURE
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LIST OF CONTENTS
CHAPTER TITLE PAGE NO
CHAPTER 1 INTRODUCTION
1.0 WHAT IS DATA ACQUISITION
1.1 DIFFERENT TYPES OF DATA ACQUISITION
1.2 NETWORKING
1.3 AIM OF THE PROJECT
CHAPTER 2 WORKING PRINCIPLE
2.0 BLOCK DIAGRAM OF DATA ACQUISITION
2.1 CIRCUIT DESCRIPTION
CHAPTER 3 DESIGN PROCEDURE
3.0 POWER SUPPLY
3.1 INTRODUCTION TO MICROCONTROLLERS
3.2 I2C PROTOCOL
3.3 LIGHT DEPENDENT RESISTORS
3.4 EEPROM
3.5 TEMPERATURE SENSOR3.6 LCD
CHAPTER 4 SOURCE CODE OF THE PROJECT
CHAPTER 5 ADVANTAGES AND APPLICATIONS
5.0 ADVANTAGES OF USING A DATA
ACQUISITION FOR COLLECTING DATA
5.1 DATA LOGGING VERSUS DATA ACQUISITION
5.2 APPLICATIONS
CHAPTER 6 CONCLUSION AND FUTURE DIRECTIONS
APPENDIX
BIBLIOGRAPHY
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CHAPTER 1
INTRODUCTION
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INTRODUCTION TO DATA ACQUISITION:
WHAT IS A DATA ACQUISITION?
A Data Acquisition is an electronic instrument used to take measurements fromsensors and store those measurements for future use. Some common measurements include
temperature, pressure, current, velocity, strain, displacement, and other physical phenomena.
This includes many data acquisition devices such as plug-in boards or serial communication
systems which use a computer as a real time data recording system. However, most instrument
manufacturers consider a data Acquisition a stand alone device that can read various types of
electrical signals and store the data in internal memory for later download to a computer.
Data loggers vary between general purpose types for a range of measurement applications to
very specific devices for measuring in one environment only. It is common for general purpose types
to be programmable however many remains as static machines with only a limited number of
changeable parameters. Electronic data loggers have replaced chart records in many applications.
1.1 DIFFERENT TYPES OF DATA ACQUISITION:
The differences between various data loggers are based on the way that data is
recorded and stored. The basic difference between the two data logger types is that one type
allows the data to be stored in a memory, to be retrieved at a later time, while the other type
automatically records the data on paper, for immediate viewing and analysis. Many data
loggers combine these two functions, usually unequally, with the emphasis on either the
ability to transfer the data or to provide a printout of it.
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1.2 HOW CAN NETWORKING BE USED FOR EXTENSIVE
CQUISITION REQUIREMENTS?
For users who must acquire data over many locations, and wish to have a single
collection/recording point, networking is a truly viable solution. With a network, one central
location is responsible for data storage and recording; data is collected by remote units in
various locations, and then fed to this master unit for storage/recording. This is a great
convenience, in that an operator can retrieve the data from one location, rather than having to
go to each individual site for collection.
1.3 AIM OF PROJECT:
To capture the data (Temperature, Sunlight etc) by using sensors for maintaining the
process control systems automatically.
COMPONENTS REQUIRED:
HARDWARE:
oMicrocontroller (AT89S52)oEEPROM (24LC64)oTemperature Sensor (DS 1621)oMulti 10 PotoLimit switchoLCD
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CHAPTER 2
WORKING PRINCIPLE
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2.0 BLOCK DIAGRAM:
LIMIT
Fig 1: BLOCKDIAGRAM OF DATA ACQUISITION
DISPLAY
EMBEDDED CONTROLERLDR
TEMP.
TRANSDUCER
EPROM
KEY BOARD
POWER SUPPLY
MULTI TURN
POT
LIMIT SWITCH
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2.1 CIRCUIT DESCRIPTION:
A soft ware program written in Embedded C is loaded in the embedded controller,
using a suitable temperature transducer (DS1621 is a Digital Thermometer and Thermostat
which measures temperature with out any external components from -55C to +125C in
0.5C incrementsand Converts it to digital word in less than 1 second). temperature of the
plant (normally a boiler) is measured and it is given as input to the embedded controller, and
this value is compared with the set temperature value which is already kept in the controller if
it exceeds the set value the LDR will be activated and the date and time at which it occurs
will be stored in the EEPROM which is kept externally.
Similarly the output of the multi turn pot indicates the changes in pressure. This
analog signal is given as input to the micro controller which will be converted as digital
signal using the built in ADC peripheral of the embedded controller this value is compared
with the set temperature value which is already kept in the controller if it exceeds the set
value the LDR will be activated and the date and time at which it occurs will be stored in the
EEPROM. Simultaneously the system will give a siren as indication this will go off if
unattended, in this manner the system can store as many as 255 records in the memory as
and when the operator want this details can be accessed using a key board and it will bedisplayed in the LCD display. A regulated power supply of required voltage is provided to
power up the circuit.
The hardware is assembled and tested for proper functioning .the programming of
micro controller involves writing the program on a PC. This may be done in either C or
Assembly. The program if written in C is compiled to generate the Hex file. The Hex file
needs to be in the INTEL Hex format. If program is written in assembly, it is compiled to
produce the obj file. Subsequently a linker is used to generate the appropriate INTEL Hex
file. Then this is programmed in to the micro controller using a programmer. The
programmed micro controller is appropriately called the firmware for the data logger.
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CHAPTER 3
DESIGN PROCEDURE
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3.0 POWER SUPPLY
Fig: POWER SUPPLY
STEP DOWN TRANSFORMER:
The step down transformer is used to step down the main supply voltage from 230V AC to
lower value. This 230V AC voltage cannot be used directly, thus it is stepped down. The transformer
consists of primary and secondary coils. To reduce or step down the voltage the transformer is
designed to contain less number of turns in its secondary core. The output from the secondary coil is
also in AC form. Thus the conversion from AC to DC is essential. This conversion is achieved by
using the rectifier circuit.
RECTIFIER:The rectifier circuit is used to convert the AC voltage into its corresponding DC voltage.
There are half wave and full wave rectifiers available for this specific function. The most important
simple device used in rectifier circuit is the diode the simple function of the diode is to conduct when
forward biased and not to conduct in reverse bias. The efficient circuit used is the full wave bridge
rectifier circuit. The output voltage of the rectifier is in ripple form. The ripples from the obtained DC
voltages are removed by using the filter circuit.
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INPUT FILTER:
Capacitors are used as filters. The ripples from the DC voltage are removed and pure DC
voltage is obtained. The primary action performed by capacitor is charging and discharging; it charges
in positive half cycle of the AC voltage and discharges during the negative half cycle. So it allows
only the AC voltage and does not allow DC voltage. This filter is fixed before the regulator thus the
output is free from ripples.
REGULATOR UNIT:
Regulator regulates the output voltage to be always constant. The output voltage is
maintained constant irrespective of the fluctuations in the input AC voltage. When the internal
resistance of the power supply is greater than 30ohms the output gets fluctuated. Thus this can be
successfully reduced here. The regulators are mainly classified for low voltage and for high voltage.
Positive regulatorregulates the positive voltage.
Negative regulatorregulates the negative voltage.
FIXED POSITIVE VOLTAGE REGULATORS:
Fig: VOLTAGE REGULATOR
The series 78XX regulators provide fixed regulated voltages from +5V to +24V. Figure
shows how one such IC, a 7805, is connected to provide voltage regulation with output from this unit
of +5V DC. An unregulated input voltage Vi is filtered by capacitor Ci and connected to the ICs IN
terminal. The ICs OUT terminal provides a regulated +5V, which is filtered by capacitor Co (mostly
for any high frequency noise). The third terminal of IC is connected to ground (GND). While the
input voltage may vary over some permissible voltage range and the output load may vary over some
acceptable range, the output voltage remains constant within specified voltage variation limits. These
limitations are spelled out in the manufacturers specification sheets.
A table of positive voltage regulated ICs is provided in the following table:
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POSITIVE VOLTAGE REGULATOR IN 7800 SERIES:
IC PART OUTPUT
VOLTAGE(V)
MINIMUM Vi(V)
7805 +5 7.3
7806 +6 8.3
7808 +8 10.5
7810 +10 12.5
7812 +12 14.6
7815 +15 17.7
7818 +18 21.0
7824 +24 27.1
OUTPUT FILTER:
The filter circuit is often fixed after the regulator circuit. Capacitor is most often used as filter.
The principle of the capacitor is to charge and discharge. It charges during the positive half cycle of
the AC voltage and discharges during the negative half cycle. So it allows only the AC voltage and
does not allow the DC voltage. This filter is fixed after the regulator circuit to filter any of the possibly
found ripples in the output received finally. The output at this stage is 5V and is given to the micro
controller PIC16F877.
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INTRODUCTION TO MICROCONTROLLER
Micro controller is a true computer on a chip the design incorporates all of the
features found in a microprocessor CPU: arithmetic and logic unit, stack pointer,
program counter and registers. It has also had added additional features like RAM,
ROM, serial I/O, counters and clock circuit.
Like the microprocessor, a microcontroller is a general purpose device, but
one that is meant to read data, perform limited calculations on that data and
control its environment based on those calculations. The prime use of a
microcontroller is to control the operation of a machine using a fixed programthat is stored in ROM and that does not change over the lifetime of the system.
The design approach of a microcontroller uses a more limited set of single
byte and double byte instructions that are used to move code and data from
internal memory to ALU. Many instructions are coupled with pins on the IC
package; the pins are capable of having several different functions depending on
the wishes of the programmer.
The microcontroller is concerned with getting the data from and on to its
own pins; the architecture and instruction set are optimized to handle data in bit
and byte size.
4.2 8051 Architecture
The generic 8051 architecture supports a Harvard architecture, which
contains two separate buses for both program and data. So, it has two distinctive
memory spaces of 64K X 8 size for both programmed and data.
It is based on an 8 bit central processing unit with an 8 bit Accumulator and
another 8 bit B register as main processing blocks. Other portions of the
architecture include few 8 bit and 16 bit registers and 8 bit memory locations.
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4.4 Block Diagram of 8051
Figure 4.1 - Block Diagram of the 8051 Core
So, very soon Intel introduced the 8051 devices with re-programmable type of
Program Memory using built-in EPROM of size 4K X 8. Like a regular EPROM,
this memory can be re-programmed many times. Later on Intel started
manufacturing these 8031 devices without any on chip Program Memory.
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4.5 Functional Blocks of 8051
4.6 Properties of Extra pins in 8051
ALE/PROG: Address Latch Enable output pulse for latching the low byte of
the address during accesses to external memory. ALE is emitted at a constant rate
of 1/6 of the oscillator frequency, for external timing or clocking purposes, even
when there are no accesses to external memory.
PSEN : Program Store Enable is the read strobe to external Program Memory.
When the device is executing out of external Program Memory, PSEN is activated
twice each machine cycle (except that two PSEN activations are skipped duringaccesses to external Data Memory). PSEN is not activated when the device is
executing out of internal Program Memory.
EA/VPP: When EA is held high the CPU executes out of internal Program
Memory (unless the Program Counter exceeds 0FFFH in the 80C51). Holding EA
low forces the CPU to execute out of external memory regardless of the Program
Counter value.
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In the 80C31, EA must be externally wired low. In the EPROM devices, this
pin also receives the programming supply voltage (VPP) during EPROM
programming.
XTAL1: Input to the inverting oscillator amplifier.
XTAL2: Output from the inverting oscillator amplifier.
4.7 Port Pin Alternate Function
P3.0- RxD (serial input port)
P3.1 -TxD (serial output port)
P3.2 -INT0 (external interrupt 0)
P3.3- INT1 (external interrupt 1)
P3.4 -T0 (timer 0 external input)
P3.5 -T1 (timer 1 external input)
P3.6 -WR (external data memory write strobe)
P3.7 -RD (external data memory read strobe)
VCC: -Supply voltage
VSS: -Circuit ground potential
All four ports in the 89C51 are bidirectional. Each consists of a latch (Special
Function Registers P0 through P3), an output driver, and an input buffer. The
output drivers of Ports 0 and 2, and the input buffers of Port 0, are used in accesses
to external memory. In this application, Port 0 outputs the low byte of the external
memory address, time-multiplexed with the byte being written or read. Port 2
outputs the high byte of the external memory address when the address is 16 bits
wide. Otherwise, the Port 2 pins continue to emit the P2 SFR content.
All the Port 3 pins are multifunctional. They are not only port pins, but also serve
the functions of various special features as listed below:
Port Pin Alternate Function
P3.0 RxD (serial input port)
P3.1 TxD (serial output port)
P3.2 INT0 (external interrupt)
P3.3 INT1 (external interrupt)
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P3.4 T0 (Timer/Counter 0 external input)
P3.5 T1 (Timer/Counter 1 external input)
P3.6 WR (external Data Memory write strobe)
P3.7 RD (external Data Memory read strobe)
4.8 Criteria for choosing a Microcontroller
1. The first and foremost criteria for choosing a microcontroller are that it must
meet task at hands efficiently and cost effectively. In analyzing the needs of a
microcontroller based project we must first see whether it is an 8-bit, 16-bit or 32-
bit microcontroller and how best it can handle the computing needs of the task
most effectively. The other considerations in this category are:
(a) Speed: The highest speed that the microcontroller supports.
(b) Packaging: Is it 40-pin DIP or QPF or some other Packaging format?
This is important in terms of space, assembling and Prototyping the end
product.
(c) Power Consumption: This is especially critical for battery powered products.
(d) The amount of RAM and ROM on chip.
(e) The number of I/O pins and timers on the chip.
(f) How easy it is to upgrade to higher performance or lower
power Consumption versions.(g) Cost per unit: This is important in terms of final product in
Which a microcontroller is used.
2. The second criteria in choosing a microcontroller are how easy it is to
develop products around it. Key considerations include the availability of an
assembler, debugger, a code efficient C language compiler, emulator, technical
support and both in house and outside expertise. In many cases third party vendor
support for chip is required.
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3. The third criteria in choosing a microcontroller is it readily available in
needed quantities both now and in future. For some designers this is even more
important than first two criterias. Currently, of leading 8bit microcontrollers, the
89C51 family has the largest number of diversified (multiple source) suppliers. By
suppliers meant a producer besides the originator of microcontroller in the case of
the 89C51, which was originated by Intel, several companies are also currently
producing the 89C51. Viz: INTEL, ATMEL, These companies include PHILIPS,
SIEMENS, and DALLAS-SEMICONDUCTOR. It should be noted that Motorola,
Zilog and Microchip Technologies have all dedicated massive resource as to
ensure wide and timely availability of their product since their product is stable,
mature and single sourced. In recent years they also have begun to sell the ASIC
library cell of the microcontroller.
5.1 Description of AT89C51
The Philips microcontrollers described in this data sheet are high-performance
static 80C51 designs. They are manufactured in an advanced CMOS process and
contain a non-volatile Flash program memory. They support both 12-clock and 6-
clock operation. The P89C51X2 and P89C52X2/54X2/58X2 contain 128 byte
RAM and 256 byte RAM respectively, 32 I/O lines, three 16-bit counter/timers, a
six-source, four-priority level nested interrupt structure, a serial I/O port for either
multi-processor communications, I/O expansion or full duplex UART, and on-chip
oscillator and clock circuits.
In addition, the devices are static designs which offer a wide range of operating
frequencies down to zero. Two software selectable modes of power reduction
idle mode and power-down modeare available. The idle mode freezes the CPU
while allowing the RAM, timers, serial port, and interrupt system to continue
functioning.
The power-down mode saves the RAM contents but freezes the oscillator,
causing all other chip functions to be in operative. Since the design is static, the
clock can be stopped without loss of user data. Then the execution can be resumed
from the point the clock was stopped.
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5.2 Features of AT89C51
AT89C51 Central Processing Unit4 Kbytes Flash (P89C51X2)
8 Kbytes Flash (P89C52X2)
16 Kbytes Flash (P89C54X2)
32 Kbytes Flash (P89C58X2)
128 byte RAM (P89C51X2)
256 byte RAM (P89C52/54X2/58X2)
Boolean processor Fully static operation
12-clock operation with selectable 6-clock operation (via software or viaparallel programmer).
Memory addressing capability Up to 64 Kbytes ROM and 64 Kbytes RAM
Power control modes: Clock can be stopped and resumed Idle mode Power-down mode
Two speed ranges
0 to 20 MHz with 6-clock operation
0 to 33 MHz with 12-clock operation
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LQFP, PLCC or DIP package Extended temperature ranges Dual Data Pointers Three security bits Four interrupt priority levels Six interrupt sources Four 8-bit I/O ports Full-duplex enhanced UART
Framing error detection
Automatic address recognition Three 16-bit timers/counters T0, T1 (standard 80C51) and additional T2
(capture and compare)
Programmable clock-out pin
Asynchronous port reset
Low EMI (inhibit ALE, slew rate controlled outputs, and 6-
Clock mode)
Wake-up from Power Down by an external interrupt
5.3 Block Diagram of AT89C51
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5.4 General Description of AT89C51
The P89C51X2/P89C52X2/P89C54X2/P89C58X2 FLASH reliably stores
memory contents even after 10,000 erase and program cycles. The cell is designed
to optimize the erase and programming mechanisms. In addition, the combination
of advanced tunnel oxide processing and low internal electric fields for erase and
programming operations produces reliable cycling.
Features
FLASH EPROM internal program memory with Chip Erase
Up to 64 byte external program memory if the internal program memory is
disabled (EA = 0)
Programmable security bits
10,000 minimum erase/program cycles for each byte
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10 year minimum data retention
Programming support available from many popular vendors
Oscillator characteristics
Using the oscillator, XTAL1 and XTAL2 are the input and output, respectively,
of an inverting amplifier. The pins can be configured for use as an on-chip
oscillator, as shown in the logic symbol. To drive the device from an external
clock source, XTAL1 should be driven while XTAL2 is left unconnected.
However, minimum and maximum high and low times specified in the data sheet
must be observed.
Clock Control Register (CKCON)
This device provides control of the 6-clock/12-clock mode by both an SFR
bit (bit X2 in register CKCON) and a Flash bit (bit FX2, located in the Security
Block). When X2 is 0, 12-clock mode is activated. By setting this bit to 1, the
system is switching to 6-clock mode. Having this option implemented as SFR bit,
it can be accessed anytime and changed to either value. Changing X2 from 0 to 1
will result in executing user code at twice the speed, since all system time intervals
will be divided by 2. Changing back from 6-clock to 12-clock mode will slow
down running code by a factor of 2.
The Flash clock control bit (FX2) activates the 6-clock mode when
programmed using a parallel programmer, super coding the X2 bit (CKCON.0).
Please also see Table 2 below.
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A 50% duty cycle clock can be programmed to be output on P1.0. This pin,
besides being a regular I/O pin, has two alternate functions. It can be programmed:
1. To input the external clock for Timer/Counter 2, or
2. To output a 50% duty cycle clock ranging from 61 Hz to 4 MHz at a 16 MHz
operating frequency in 12-clock mode (122 Hz to 8 MHz in 6-clock mode).
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (in T2CON)
must be cleared and bit T20E in T2MOD must be set. Bit TR2 (T2CON.2) also
must be set to start the timer. The Clock-Out frequency depends on the
oscillator frequency and the reload value of Timer 2 capture registers (RCAP2H,
RCAP2L) as shown in this equation: Oscillator Frequency
n_ (65536RCAP2H, RCAP2L)
Where:
n = 2 in 6-clock mode, 4 in 12-clock mode.
(RCAP2H, RCAP2L) = the content of RCAP2H and RCAP2L
Taken as a 16-bit unsigned integer.
In the Clock-Out mode Timer 2 roll-overs will not generate an interrupt. This is
similar to when it is used as a baud-rate generator. It is possible to use Timer 2 as a
baud-rate generator and a clock generator simultaneously.
RESET
A reset is accomplished by holding the RST pin HIGH for at least two machine
cycles (24 oscillator periods in 12-clock and 12 oscillator periods in 6-clock
mode), while the oscillator is running. To insure a reliable power-up reset, the RST
pin must be high long enough to allow the oscillator time to start up (normally a
few milliseconds) plus two machine cycles, unless it has been set to 6-clock
operation using a parallel programmer.
5.5 Timer 0 and Timer 1 Operation
The Timer or Counter function is selected by control bits C/T in the
Special Function Register TMOD. These two Timer/Counters have four operating
modes, which are selected by bit-pairs (M1, M0) in TMOD. Modes 0, 1, and 2 are
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the same for both Timers/Counters. Mode 3 is different. The four operating modes
are described in the following text.
Mode 0
Putting either Timer into Mode 0 makes it look like an 8048 Timer, which is
an 8-bit Counter with a divide-by-32 prescaler. Figure 2 shows the Mode 0
operation. In this mode, the Timer register is configured as a 13-bit register.
As the count rolls over from all 1s to all 0s, it sets the Timer interrupt flag
TFn. The counted input is enabled to the Timer when TRn = 1 and either GATE =
0 or INTn = 1. (Setting GATE = 1 allows the Timer to be controlled by external
input INTn, to facilitate pulse width measurements). TRn is a control bit in the
Special Function Register TCON (Figure 3).
The 13-bit register consists of all 8 bits of THn and the lower 5 bits of TLn.
The upper 3 bits of TLn are indeterminate and should be ignored. Setting the run
flag (TRn) does not clear the registers. Mode 0 operation is the same for Timer 0
as for Timer 1. There are two different GATE bits, one for Timer 1 (TMOD.7) and
one for Timer 0 (TMOD.3).
Mode 1
Mode 1 is the same as Mode 0, except that the Timer register is being run
with all 16 bits.
Mode 2
Mode 2 configures the Timer register as an 8-bit Counter (TLn) with
automatic reloads, as shown in Figure 4. Overflow from TLn not only sets TFn,
but also reloads TLn with the contents of THn, which is preset by software. The
reload leaves THn unchanged. Mode 2 operation is the same for Timer 0 as for
Timer 1.
Mode 3
Timer 1 in Mode 3 simply holds its count. The effect is the same as setting
TR1 = 0. Timer 0 in Mode 3 establishes TL0 and TH0 as two separate counters.
The logic for Mode 3 on Timer 0 is shown in Figure 5. TL0 uses the Timer 0
control bits: C/T, GATE, TR0, and TF0 as well as pin INT0. TH0 is locked into a
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timer function (counting machine cycles) and takes over the use of TR1 and TF1
from Timer 1. Thus, TH0 now controls the Timer 1 interrupt.
Mode 3 is provided for applications requiring an extra 8-bit timer on the
counter. With Timer 0 in Mode 3, an 80C51 can look like it has three
Timer/Counters. When Timer 0 is in Mode 3, Timer 1 can be turned on and off by
switching it out of and into its own Mode 3, or can still be used by the serial port
as a baud rate generator, or in fact, in any application not requiring an interrupt.
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TIMER 2 OPERATION
Timer 2
Timer 2 is a 16-bit Timer/Counter which can operate as either an event timer or
an event counter, as selected by C/T2 in the special function register T2CON (see
Figure 6). Timer 2 has three operating modes: Capture, Auto-reload (up or down
counting), and Baud Rate Generator, which are selected by bits in the T2CON as
shown in Table 4.
Capture Mode
In the capture mode there are two options which are selected by bit EXEN2 in
T2CON. If EXEN2=0, then timer 2 is a 16-bit timer or counter (as selected by
C/T2 in T2CON) which, upon overflowing, sets bit TF2, the timer 2 overflow bit.
This bit can be used to generate an interrupt (by enabling the Timer 2 interrupt bit
in the IE register).
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If EXEN2=1, Timer 2 operates as described above, but with the added feature
that a 1-to-0 transition at external input T2EX causes the current value in the
Timer 2 registers, TL2 and TH2, to be captured into registers RCAP2L and
RCAP2H, respectively.
In addition, the transition at T2EX causes bit EXF2 in T2CON to be set, and
EXF2 (like TF2) can generate an interrupt (which vectors to the same location as
Timer 2 overflow interrupt. The Timer 2 interrupt service routine can interrogate
TF2 and EXF2 to determine which event caused the interrupt). The capture mode
is illustrated in Figure 7 (There is no reload value for TL2 and TH2 in this mode.
Even when a capture event occurs from T2EX, the counter keeps on counting
T2EX pin transitions or osc/12 (12-clock Mode) or osc/6 (6-clock Mode) pulses).
Baud Rate Generator Mode
Bits TCLK and/or RCLK in T2CON (Table 4) allow the serial port transmit and
receive baud rates to be derived from either Timer 1 or Timer 2. When TCLK= 0,
Timer 1 is used as the serial port transmit baud rate generator. When TCLK= 1,
Timer 2 is used as the serial port transmit baud rate generator.
RCLK has the same effect for the serial port receive baud rate. With these
two bits, the serial port can have different receive and transmit baud rates one
generated by Timer 1, the other by Timer 2. Figure 11 shows the Timer 2 in baud
rate generation mode. The baud rate generation mode is like the auto-reload mode,
in that a rollover in TH2 causes the Timer 2 registers to be reloaded with the 16-bit
value in registers RCAP2H and RCAP2L, which are preset by software. The baud
rates in modes 1 and 3 are determined by Timer 2s overflow rate given below:
Modes 1 and 3 Baud Rates _ Timer 2 Overflow Rate 16 The timer can be
configured for either timer or counter operation. In many applications, it is
configured for timer operation (C/T2=0). Timer operation is different for Timer
2 when it is being used as a baud rate generator.
Usually, as a timer it would increment every machine cycle (i.e., 1/6 the
oscillator frequency in 6-clock mode or 1/12 the oscillator frequency in 12-clock
mode). As a baud rate generator, it increments at the oscillator frequency in 6-
clock mode or at 1/2 the oscillator frequency in 12-clock mode.
Thus the baud rate formula is as follows:
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Where:
n = 16 in 6-clock mode, 32 in 12-clock mode.
(RCAP2H, RCAP2L)= The content of RCAP2H and RCAP2L taken as a 16-bit
unsigned integer.
The Timer 2 as a baud rate generator mode shown in Figure 11 is valid only if
RCLK and/or TCLK = 1 in T2CON register. Note that a rollover in TH2 does not
set TF2, and will not generate an interrupt.
Thus, the Timer 2 interrupt does not have to be disabled when Timer 2 is in the
baud rate generator mode. Also if the EXEN2 (T2 external enable flag) is set, a 1-
to-0 transition in T2EX (Timer/counter 2 trigger input) will set EXF2 (T2 external
flag) but will not cause a reload from (RCAP2H, RCAP2L) to (TH2, TL2).
Therefore when Timer 2 is in use as a baud rate generator, T2EX can be used as an
additional external interrupt, if needed. When Timer 2 is in the baud rate generator
mode, one should not try to read or write TH2 and TL2. As a baud rate generator,
Timer 2 is incremented every state time (osc/2) or asynchronously from pin T2;
under these conditions, a read or write of TH2 or TL2 may not be accurate. The
RCAP2 registers may be read, but should not be written to; because a write might
overlap a reload and cause write and/or reload errors. The timer should be turned
off (clear TR2) before accessing the Timer 2 or RCAP2 registers. Table 5 shows
commonly used baud rates and how they can be obtained from Timer 2.
.
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Summary of Baud Rate Equations
Timer 2 is in baud rate generating mode. If Timer 2 is being clocked through pin
T2 (P1.0) the baud rate is:
If Timer 2 is being clocked internally, the baud rate is:
Where:
n = 16 in 6-clock mode, 32 in 12-clock mode.
fOSC= Oscillator Frequency
To obtain the reload value for RCAP2H and RCAP2L, the above
Equation can be rewritten as:
Timer/Counter 2 Set-up
Except for the baud rate generator mode, the values given for
T2CON do not include the setting of the TR2 bit. Therefore, bit TR2 must be set,
separately, to turn the timer on. See Table 6 for set-up of Timer 2 as a timer.
Also see Table 7 for set-up of Timer 2 as a counter
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NOTES:
1. Capture/reload occurs only on timer/counter overflow.
2. Capture/reload occurs on timer/counter overflow and a 1-to-0 transition on
T2EX (P1.1) pin except when Timer 2 is used in the baud rate generator mode.
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3.2I2C PROTOCOL
HISTORY OF THE I2C BUS
The I2C bus was developed in the early 1980's by Philips Semiconductors. Its original
purpose was to provide an easy way to connect a CPU to peripheral chips in a TV-set. IC is a
multi-master serial computer bus used to attach low-speed peripherals to a motherboard,
embedded system, or cell phone. The name stands for Inter-Integrated Circuit and is
pronounced I-squared-C and also, I-two-C.
THE I2C BUS PROTOCOL
The I2C bus physically consists of 2 active wires and a ground connection. The active
wires, called SDA and SCL, are both bi-directional. SDA is the Serial data line, and SCL is
the Serial clock line.
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Every device hooked up to the bus has its own unique address, no matter whether it is
an MCU, LCD driver, memory, or ASIC. Each of these chips can act as a receiver and/or
transmitter, depending on the functionality. Obviously, an LCD driver is only a receiver,
while a memory or I/O chip can be both transmitter and receiver.The I2C bus is a multi-
master bus. This means that more than one IC capable of initiating a data transfer can be
connected to it. The I2C protocol specification states that the IC that initiates a data transfer
on the bus is considered the Bus Master. Consequently, at that time, all the other ICs are
regarded to be Bus Slaves As bus masters are generally microcontrollers, let's take a look at
a general 'inter-IC chat' on the bus. Lets consider the following setup and assume the MCU
wants send data to one of its slaves.
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OPERATION:
First, the MCU will issue a START condition. This acts as an 'Attention' signal to all
of the connected devices. All ICs on the bus will listen to the bus for incoming data.
Then the MCU sends the ADDRESS of the device it wants to access, along with an
indication whether the access is a Read or Write operation (Write in our example). Having
received the address, all IC's will compare it with their own address. If it doesn't match, they
simply wait until the bus is released by the stop condition (see below). If the address matches,
however, the chip will produce a response called the ACKNOWLEDGEMENT signal.
Once the MCU receives the acknowledge, it can start transmitting or receiving
DATA. In our case, the MCU will transmit data. When all is done, the MCU will issue the
STOP condition. This is a signal that the bus has been released and that the connected ICs
may expect another transmission to start any moment.
We have had several states on the bus in our example: START, ADDRSS,
ACKNOWLEDGEMENT, DATA and STOP. These are all unique conditions on the bus.
Before we take a closer look at these bus conditions we need to understand a bit about the
physical structure and hardware of the bus.
THE I2C BUS HARDWARE STRUCTURE
As explained earlier, the bus physically consists of 2 active wires called SDA (data)
and SCL (clock), and a ground connection.
Both SDA and SCL are initially bi-directional. This means that in a particular device,
these lines can be driven by the IC itself or from an external device. In order to achieve this
functionality, these signals use open collector or open drain outputs (depending on the
technology).
The bus interface is built around an input buffer and an open drain or open collector
transistor. When the bus is IDLE, the bus lines are in the logic HIGH state (note that external
pull-up resistors are necessary for this which is easily forgotten). To put a signal on the bus,
the chip drives its output transistor, thus pulling the bus to a LOW level. The "pull-up
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resistor" in the devices as seen in the figure is actually a small current source or even non-
existent.
I2C Bus Events: The START and STOP conditions:
Prior to any transaction on the bus, a START condition needs to be issued on the bus.
The start condition acts as a signal to all connected IC's that something is about to be
transmitted on the bus. As a result, all connected chips will listen to the bus.
After a message has been completed, a STOP condition is sent. This is the signal for
all devices on the bus that the bus is available again (idle). If a chip was accessed and has
received data during the last transaction, it will now process this information (if not already
processed during the reception of the message).
START: The chip issuing the Start condition first pulls the SDA (data) line low, and next
pulls the SCL (clock) line low.
STOP: The Bus Master first releases the SCL and then the SDA line.
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A single message can contain multiple Start conditions. The use of this so- called"repeated start" is common in I2C.
A Stop condition always denotes the END of a transmission. Even if it is issued inthe middle of a transaction or in the middle of a byte. It is "good behavior" for a
chip that, in this case, it disregards the information sent and resumes the "listening
state", waiting for a new start condition.
I2C BUS EVENTS: TRANSMITTING A BYTE TO A SLAVE:
Once the start condition has been sent, a byte can be transmitted by the MASTER to
the SLAVE.
This first byte after a start condition will identify the slave on the bus (address) and
will select the mode of operation. The meaning of all following bytes depends on the slave.
As the I2C bus gained popularity, it was soon discovered that the number of available
addresses was too small. Therefore, one of the reserved addresses has been allocated to a new
task to switch to 10-bit addressing mode. If a standard slave (not able to resolve extended
addressing) receives this address, it won't do anything (since it's not its address).
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If there are slaves on the bus that can operate in the extended 10-bit addressing mode,
they will ALL respond to the ACK cycle issued by the master. The second byte that gets
transmitted by the master will then be taken in and evaluated against their address.
I2C BUS EVENTS: RECEIVING A BYTE FROM A SLAVE:
Once the slave has been addressed and the slave has acknowledged this, a byte can
be received from the slave if the R/W bit in the address was set to READ (set to '1').
The protocol syntax is the same as in transmitting a byte to a slave, except that now
the master is not allowed to touch the SDA line. Prior to sending the 8 clock pulses needed to
clock in a byte on the SCL line, the master releases the SDA line. The slave will now takecontrol of this line. The line will then go high if it wants to transmit a '1' or, if the slave wants
to send a '0', remain low.
All the master has to do is generate a rising edge on the SCL line (2), read the level on
SDA (3) and generate a falling edge on the SCL line (4). The slave will not change the data
during the time that SCL is high. (Otherwise a Start or Stop condition might inadvertently
be generated.)
During (1) and (5), the slave may change the state of the SDA line.
In total, this sequence has to be performed 8 times to complete the data byte. Bytes
are always transmitted MSB first
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The meaning of all bytes being read depends on the slave. There is no such thing as a
"universal status register". You need to consult the data sheet of the slave being addressed to
know the meaning of each bit in any byte transmitted.
I2C BUS EVENTS: GETTING ACKNOWLEDGE FROM A SLAVE:
When an address or data byte has been transmitted onto the bus then this must be
acknowledged by the slave(s). In case of an address: If the address matches its own then that
slave and only that slave will respond to the address with an ACK. In case of a byte
transmitted to an already addressed slave then that slave will respond with an ACK as well.
The slave that is going to give an ACK pulls the SDA line low immediately after
reception of the 8th bit transmitted, or, in case of an address byte, immediately after
evaluation of its address. In practical applications this will not be noticeable.
This means that as soon as the master pulls SCL low to complete the transmission of
the bit (1), SDA will be pulled low by the slave (2).
The master now issues a clock pulse on the SCL line (3). The slave will release the
SDA line upon completion of this clock pulse (4).
The bus is now available again for the master to continue sending data or to generate a
stop condition.
In case ofdata being written to a slave, this cycle must be completed before a stop
condition can be generated. The slave will be blocking the bus (SDA kept low by slave) until
the master has generated a clock pulse on the SCL line.
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I2C BUS EVENTS: GIVING ACKNOWLEDGE TO A SLAVE:
Upon reception of a byte from a slave, the master must acknowledge this to the
slave device.
The master is in full control of the SDA and the SCL line.
After transmission of the last bit to the master (1) the slave will release the SDA line.
The SDA line should then go high (2). The Master will now pull the SDA line low (3) .
Next, the master will put a clock pulse on the SCL line (4). After completion of this
clock pulse, the master will again release the SDA line (5).The slave will now regain control
of the SDA line (6).
If the master wants to stop receiving data from the slave, it must be able to send a
stop condition.
Since the slave regains control of the SDA line after the ACK cycle issued by the
master, this could lead to problems.
Let's assume the next bit ready to be sent to the master is a 0. The SDA line would be
pulled low by the slave immediately after the master takes the SCL line low. The master now
attempts to generate a Stop condition on the bus. It releases the SCL line first and then tries to
release the SDA line - which is held low by the slave. Conclusion: No Stop condition has
been generated on the bus.
This condition is called a NACK: Not acknowledge.
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I2C BUS EVENTS: NO ACKNOWLEDGE (FROM SLAVE TO
MASTER):
This is not exactly a condition. It is merely a state in the data flow between master and
slave.
If, after transmission of the 8th bit from the master to the slave the slave does not pull
the SDA line low, then this is considered a No ACK condition.
This means that either:
The slave is not there (in case of an address) The slave missed a pulse and got out of sync with the SCL line of the master. The bus is "stuck". One of the lines could be held low permanently.
In any case the master should abort by attempting to send a stop condition on the bus.
APPLICATIONS
IC is appropriate for peripherals where simplicity and low manufacturing cost are more
important than speed. Common applications of the IC bus are:
Reading configuration data from SPD EEPROMs on SDRAM, DDR SDRAM, DDR2SDRAM memory sticks (DIMM) and other stacked PC boards
Supporting systems management for PCI cards, through a SMBus 2.0 connection. Accessing NVRAM chips that keep user settings. Accessing low speed DACs. Accessing low speed ADCs. Changing contrast, hue, and color balance settings in monitors (Display Data
Channel).
Changing sound volume in intelligent speakers. Controlling OLED/LCD displays, like in a cell phone. Reading hardware monitors and diagnostic sensors, like a CPU thermostat and fan
speed.
Reading real time clocks.
http://en.wikipedia.org/wiki/Serial_Presence_Detecthttp://en.wikipedia.org/wiki/SDRAMhttp://en.wikipedia.org/wiki/DDR_SDRAMhttp://en.wikipedia.org/wiki/DDR2_SDRAMhttp://en.wikipedia.org/wiki/DDR2_SDRAMhttp://en.wikipedia.org/wiki/DIMMhttp://en.wikipedia.org/wiki/NVRAMhttp://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/Analog-to-digital_converterhttp://en.wikipedia.org/wiki/Display_Data_Channelhttp://en.wikipedia.org/wiki/Display_Data_Channelhttp://en.wikipedia.org/wiki/Organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Real-time_clockhttp://en.wikipedia.org/wiki/Real-time_clockhttp://en.wikipedia.org/wiki/Liquid_crystal_displayhttp://en.wikipedia.org/wiki/Organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Display_Data_Channelhttp://en.wikipedia.org/wiki/Display_Data_Channelhttp://en.wikipedia.org/wiki/Analog-to-digital_converterhttp://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/NVRAMhttp://en.wikipedia.org/wiki/DIMMhttp://en.wikipedia.org/wiki/DDR2_SDRAMhttp://en.wikipedia.org/wiki/DDR2_SDRAMhttp://en.wikipedia.org/wiki/DDR_SDRAMhttp://en.wikipedia.org/wiki/SDRAMhttp://en.wikipedia.org/wiki/Serial_Presence_Detect -
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Turning on and turning off the power supply of system components.A particular strength of IC is that a microcontroller can control a network of device chips
with just two general-purpose I/O pins and software.
Peripherals can also be added to or removed from the IC bus while the system is running,
which makes it ideal for applications that require hot swapping of components.
http://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Hot_swappinghttp://en.wikipedia.org/wiki/Hot_swappinghttp://en.wikipedia.org/wiki/Microcontroller -
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3.3 LIGHT DEPENDENT RESISTOR
INTRODUCTION:
An LDR (Light dependent resistor), as its name suggests, offers resistance in response to the
ambient light. The resistance decreases as the intensity of incident light increases, and vice
versa. In the absence of light, LDR exhibits a resistance of the order of mega-ohms which
decreases to few hundred ohms in the presence of light. It can act as a sensor, since a varying
voltage drop can be obtained in accordance with the varying light. It is made up of cadmium
sulphide (CdS).
An LDR has a zigzag cadmium sulphide track. It is a bilateral device, i.e., conducts in both
directions in same fashion.
A Light Dependent Resistor (aka LDR, photoconductor, or photocell) is a device which has
a resistance which varies according to the amount of light falling on its surface.
A typical light dependent resistor is pictured above together with (on the right hand side) its
circuit diagram symbol. Different LDR's have different specifications, however theLDR's we
sell in the REUK Shop are fairly standard and have a resistance in total darkness of 1 MOhm,
and a resistance of a couple of kOhm in bright light (10-20kOhm @ 10 lux, 2-4kOhm @ 100.
`
http://www.reuk.co.uk/buy-MINI-LDR.htmhttp://www.reuk.co.uk/buy-MINI-LDR.htmhttp://www.reuk.co.uk/buy-MINI-LDR.htmhttp://www.reuk.co.uk/buy-MINI-LDR.htmhttp://www.reuk.co.uk/REUK-Products-For-Sale.htmhttp://www.reuk.co.uk/REUK-Products-For-Sale.htmhttp://www.reuk.co.uk/buy-MINI-LDR.htmhttp://www.reuk.co.uk/buy-MINI-LDR.htm -
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Uses for Light Dependent Resistors
Light dependent resistors are a vital component in any electric circuit which is to be turned on
and off automatically according to the level of ambient light - for example, solar powered
garden lights, and night security lighting.
An LDR can even be used in a simple remote control circuit using the backlight of a mobile
phone to turn on a device - call the mobile from anywhere in the world, it lights up the LDR,
and lighting (or a garden sprinkler) can be turned on remotely!
Light Dependent Resistor Circuits
There are two basic circuits using light dependent resistors - the first is activated by
darkness, the second is activated by light. The two circuits are very similar and just require
an LDR, some standard resistors, a variable resistor (aka potentiometer), and any small
signal transistor
In the circuit diagram above, theLED lights up whenever the LDR is in darkness. The 10K
variable resistor is used to fine-tune the level of darkness required before the LED lights up.
The 10K standard resistor can be changed as required to achieve the desired effect, although
any replacement must be at least 1K to protect the transistor from being damaged by
excessive current.
http://www.reuk.co.uk/electric-circuit.htmhttp://www.reuk.co.uk/Solar-Powered-Irrigation.htmhttp://www.reuk.co.uk/Resistor-Colour-Codes.htmhttp://www.reuk.co.uk/buy-VARIABLE-RESISTORS.htmhttp://www.reuk.co.uk/What-is-a-Transistor.htmhttp://www.reuk.co.uk/buy-5MM-RED-LED.htmhttp://www.reuk.co.uk/buy-5MM-RED-LED.htmhttp://www.reuk.co.uk/buy-5MM-RED-LED.htmhttp://www.reuk.co.uk/What-is-a-Transistor.htmhttp://www.reuk.co.uk/buy-VARIABLE-RESISTORS.htmhttp://www.reuk.co.uk/Resistor-Colour-Codes.htmhttp://www.reuk.co.uk/Solar-Powered-Irrigation.htmhttp://www.reuk.co.uk/electric-circuit.htm -
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By swapping the LDR over with the 10K and 10K variable resistors (as shown above), the
circuit will be activated instead by light. Whenever sufficient light falls on the LDR
(manually fine-tuned using the 10K variable resistor), the LED will light up.
Using an LDR in the Real World
The circuits shown above are not practically useful. In a real world circuit, the LED (and
resistor) between the positive voltage input (Vin) and the collector (C) of the transistor would
be replaced with the device to be powered.
Typically arelayis used - particularly when the low voltage light detecting circuit is used to
switch on (or off) a 240V mains powered device. A diagram of that part of the circuit is
shown above. When darkness falls (if the LDR circuit is configured that way around),
the relay is triggered and the 240V device - for example a security light - switches on.
http://www.reuk.co.uk/Relays-and-Renewable-Energy.htmhttp://www.reuk.co.uk/Relays-and-Renewable-Energy.htmhttp://www.reuk.co.uk/Relays-and-Renewable-Energy.htmhttp://www.reuk.co.uk/Relays-and-Renewable-Energy.htm -
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3.5 TEMPERATURE TRANSDUCER
DS-1621
TRANSDUCER : A transducer is a device, usually electrical, electronic, electro-
mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energyor
physical attribute to another for various purposes including measurement or information
transfer (for example,pressure sensors).
TYPES OF TRANSDUCERS:
ELECTROMAGNETIC: Antenna- converts electromagnetic waves into electric current and vice versa. Cathode ray tube (CRT) - converts electrical signals into visual form Fluorescent lamp, light bulb - converts electrical power into visible light Magnetic cartridge- converts motion into electrical form PhotodetectororPhotoresistor(LDR) - converts changes in light levels into resistance
changes
ELECTROCHEMICAL: PH probes Electro-galvanic fuel cell
ELECTROMECHANICAL: Electro active polymers Galvanometer MEMS Rotary motor, linear motor Vibration powered generator Potentiometer when used for measuring position Load cell converts force to mV/V electrical signal using strain gauge
http://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electro-mechanicalhttp://en.wikipedia.org/wiki/Electro-mechanicalhttp://en.wikipedia.org/wiki/Electro-mechanicalhttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Photonichttp://en.wikipedia.org/wiki/Photonichttp://en.wikipedia.org/wiki/Photovoltaichttp://en.wikipedia.org/wiki/Photovoltaichttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Pressure_sensorhttp://en.wikipedia.org/wiki/Pressure_sensorhttp://en.wikipedia.org/wiki/Pressure_sensorhttp://en.wikipedia.org/wiki/Antenna_%28radio%29http://en.wikipedia.org/wiki/Antenna_%28radio%29http://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Light_bulbhttp://en.wikipedia.org/wiki/Magnetic_cartridgehttp://en.wikipedia.org/wiki/Magnetic_cartridgehttp://en.wikipedia.org/wiki/Photodetectorhttp://en.wikipedia.org/wiki/Photodetectorhttp://en.wikipedia.org/wiki/Photoresistorhttp://en.wikipedia.org/wiki/Photoresistorhttp://en.wikipedia.org/wiki/Photoresistorhttp://en.wikipedia.org/wiki/Photoresistorhttp://en.wikipedia.org/wiki/Photodetectorhttp://en.wikipedia.org/wiki/Magnetic_cartridgehttp://en.wikipedia.org/wiki/Light_bulbhttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Antenna_%28radio%29http://en.wikipedia.org/wiki/Pressure_sensorhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Photovoltaichttp://en.wikipedia.org/wiki/Photonichttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Electro-mechanicalhttp://en.wikipedia.org/wiki/Electro-mechanicalhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electricity -
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ELECTROACOUSTIC: Geophone - convert a ground movement (displacement) into voltage Gramophone pick-up Hydrophone - converts changes in water pressure into an electrical form Loudspeaker, earphone - converts changes in electrical signals into acoustic form Microphone - converts changes in air pressure into an electrical signal Piezoelectric crystal - converts pressure changes into electrical form Tactile transducer
ELECTROSTATIC: Electrometer
THERMOELECTRIC: RTD Resistance Temperature Detector Thermocouple Peltier cooler Thermistor (includes PTC resistor and NTC resistor)
RADIO ACOUSTIC: Receiver (radio) Eiger-Mller tube used for measuring radioactivity.
TEMPERATURE TRANSDUCER USED:
DS 1621 Digital Thermometer and Thermostat.
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WHY DS1621??
DS1621 is a Digital Thermometer and Thermostat which measures temperature with
out any external components from -55C to +125C in 0.5C incrementsand Converts it to
digital word in less than 1 second. Temperature is read as a 9-bit value (2-byte transfer). It
also providesa wide power supply range of 2.7V to 5.5V.It is available in 8-pin DIP or SO
package (150mil and 208mil) with a price of 200-300. DS1621 well supports I2c
communication protocol.
Because of all the available features and considering its low cost we can say it best
suits the application of DATA LOGGER.
PIN ASSIGNMENT
PIN DESCRIPTION
SDA - 2-Wire Serial Data Input/Output A0 - Chip Address Input
SCL - 2-Wire Serial Clock A1 - Chip Address InputGNDGround A2 - Chip Address Input
TOUT - Thermostat Output Signal VDD - Power Supply Voltage
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DESCRIPTION:
The DS1621 Digital Thermometer and Thermostat provides 9-bit temperature
readings, which indicate the temperature of the device. The thermal alarm output, TOUT, isactive when the temperature of the device exceeds a user-defined temperature TH. The output
remains active until the temperature drops below user defined temperature TL, allowing for
any hysteresis necessary.
User-defined temperature settings are stored in nonvolatile memory so parts may be
programmed prior to insertion in a system. Temperature settings and temperature readings are
all communicated to/from the DS1621 over a simple 2-wire serial interface.
DETAILED PIN DESCRIPTION :
OPERATION:
MEASURING TEMPERATURE:-
A block diagram of the DS1621 is shown in Figure 1.The DS1621 measures
temperature using a band gap-based temperature sensor. A delta-sigma analog-to digital
converter (ADC) converts the measured temperature to a digital value that is calibrated in C;for F applications, a lookup table or conversion routine must be used.
The temperature reading is provided in a 9-bit, twos complement reading by issuing
the READ TEMPERATURE command. The data is transmitted through the 2-wire serial
interface, MSB first. The DS1621 can measure temperature over the range of -55_C to
+125_C in 0.5_C increments.
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Figure 1. DS1621 FUNCTIONAL BLOCK DIAGRAM
Table 2. TEMPERATURE/DATA RELATIONSHIPS
Since data is transmitted over the 2-wire bus MSB first, temperature data may be
written to/read from the DS1621 as either a single byte (with temperature resolution of 1_C)
or as two bytes. The second byte would contain the value of the least significant (0.5_C) bit
of the temperature reading as shown in Table 1.Note that the remaining 7 bits of this byte
are set to all "0"s
.
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Temperature is represented in the DS1621 in terms of a _C LSB, yielding the
following
9-bit format:
TEMPERATURE, TH, and TL FORMAT FOR T= -25_C
OPERATION AND CONTROL
The DS1621 must have temperature settings resident in the TH and TL registers for
thermostatic operation. A configuration/status register also determines the method of
operation that the DS1621 will use in a particular application, as well as indicating the status
of the temperature conversion operation.
The configuration register is defined as follows:
Where
DONE = Conversion done bit. 1 = Conversion complete, 0 = Conversion inprogress.
THF = Temperature High Flag. This bit will be set to 1 when the temperature isgreater than or equal to the value of TH. It will remain 1 until reset by writing 0
into this location or removing power from the device. This feature provides a method
of determining if the DS1621 has ever been subjected to temperatures above TH
while power has been applied.
TLF = Temperature Low Flag. This bit will be set to 1 when the temperature is lessthan or equal to the value of TL. It will remain 1 until reset by writing 0 into this
location or removing power from the device. This feature provides a method of
determining if the DS1621 has ever been subjected to temperatures below TL while
power has been applied.
NVB = Nonvolatile Memory Busy flag. 1 = Write to an E2 memory cell in progress,0 =nonvolatile memory is not busy. A copy to E2 may take up to 10 ms.
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POL = Output Polarity Bit. 1 = active high, 0 = active low. This bit isnonvolatile.
1SHOT = One Shot Mode. If 1SHOT is 1, the DS1621 will perform onetemperature conversion upon receipt of the Start Convert T protocol. If 1SHOT is 0,
the DS1621 will continuously perform temperature conversions. This bit is
nonvolatile.
X = Reserved.2-WIRE SERIAL DATA BUS
The DS1621 supports a bi-directional 2-wire bus and data transmission protocol. A
device that sends data onto the bus is defined as a transmitter, and a device receiving data as a
receiver. The device that controls the message is called a master." The devices that are
controlled by the master are slaves." The bus must be controlled by a master device, which
generates the serial clock (SCL), controls the bus access, and generates the START and
STOP conditions. The DS1621 operates as a slave on the 2-wire bus.
Connections to the bus are made via the open-drain I/O lines SDA and SCL.
The following bus protocol has been defined (See Figure 4):
Data transfer may be initiated only when the bus is not busy. During data transfer, the data line must remain stable whenever the clock line is
HIGH. Changes in the data line while the clock line is high will be interpreted as
control signals.
Accordingly, the following bus conditions have been defined:
Bus not busy: Both data and clock lines remain HIGH. Start data transfer: A change in the state of the data line, from HIGH to LOW,
while the clock is HIGH, defines a START condition.
Stop data transfer: A change in the state of the data line, from LOW to HIGH, whilethe clock line is HIGH, defines the STOP condition.
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Data valid: The state of the data line represents valid data when, after a STARTcondition, the data line is stable for the duration of the HIGH period of the clock
signal. The data on the line must be changed during the LOW period of the clock
signal. There is one clock pulse per bit of data.
Within the bus specifications a regular mode (100 kHz clock rate) and a fast mode (400 kHz
clock rate) are defined. The DS1621 works in both modes.
Acknowledge: Each receiving device, when addressed, is obliged to generate anacknowledge after the reception of each byte. The master device must generate an
extra clock pulse which is associated with this acknowledge bit.
A device that acknowledges must pull down the SDA line during the acknowledge
clock pulse in such a way that the SDA line is stable LOW during the HIGH period of
the acknowledge related clock pulse. Of course, setup and hold times must be taken
into account. A master must signal an end of data to the slave by not generating an
acknowledge bit on the last byte that has been clocked out of the slave. In this case,
the slave must leave the data line HIGH to enable the master to generate the STOP
condition.
Figure 4. DATA TRANSFER ON 2-WIRE SERIAL BUS
Figure 4 details how data transfer is accomplished on the 2-wire bus. Depending upon
the state of the R/W bit, two types of data transfer are possible:
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1. Data transfer from a master transmitter to a slave receiver. The first bytetransmitted by the master is the slave address. Next follows a number of data bytes.
The slave returns an acknowledge bit after each received byte.
2. Data transfer from a slave transmitter to a master receiver. The master transmitsthe first byte, the slave address. The slave then returns an acknowledge bit. Next
follows a number of data bytes transmitted by the slave to the master. The master
returns an acknowledge bit after all received bytes other than the last byte. At the end
of the last received byte, a not acknowledge is returned.
The master device generates all of the serial clock pulses and the START and STOP
conditions. A transfer is ended with a STOP condition or with a repeated START condition.
Since a repeated START condition is also the beginning of the next serial transfer, the bus
will not be released
COMMAND SET
Data and control information is read from and written to the DS1621 in the format
shown in Figure 5. To write to the DS1621, the master will issue the slave address of theDS1621 and the R/Wbit will be set to 0. After receiving an acknowledge, the bus master
provides a command protocol. After receiving this protocol, the DS1621 will issue an
acknowledge and then the master may send data to the DS1621. If the DS1621 is to be read,
the master must send the command protocol as before and then issue a repeated START
condition and the control byte again, this time with the R/W bit set to 1 to allow reading of
the data from the DS1621. The command set for the DS1621 as shown in Table 3 is as
follows:
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ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground -0.5V to +6.0V
Operating Temperature Range -55_C to +125_C
Storage Temperature Range -55_C to +125_C
Soldering Temperature See IPC/JEDEC J-STD-020A specification
Supply voltage range 2.7V to 5.5V
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DC ELECTRICAL CHARACTERISTICS (-55C to +125C; VDD = 2.7V
to 5.5V)
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TIMING DIAGRAM:
RECOMMENDED DC OPERATING CONDITIONS
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AC ELECTRICAL CHARACTERISTICS (-55C to +125C; VDD = 2.7V to 5.5V)
* Refer Note 3 In Appendix-C
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3.6 LCD LIQUID CRYSTAL DISPLAY
INTRODUCTION:
A liquidcrystal display (LCD) is a thin, flat display device made up of any number of
color or monochrome pixels arrayed in front of a light source or reflector. It is often utilized
in battery-powered electronic devices because it uses very small amounts of electric power.
OVERVIEW:
Each pixelof an LCD typically consists of a layer of molecules aligned between two
transparentelectrodes, and two polarizing filters, the axes of transmission of which are (in
most of the cases) perpendicular to each other. With no liquid crystal between the polarizing
filters, light passing through the first filter would be blocked by the second (crossed)
polarizer.
The surfaces of the electrodes that are in contact with the liquid crystal material are
treated so as to align the liquid crystal molecules in a particular direction. This treatment
typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a
cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing.
Electrodes are made of a transparent conductor called "ITO" or Indium Tin Oxide.
Before applying an electric field, the orientation of the liquid crystal molecules is
determined by the alignment at the surfaces. In a twisted nematic device (still the most
common liquid crystal device), the surface alignment directions at the two electrodes are
perpendicular to each other, and so the molecules arrange themselves in a helical structure, or
twist. Because the liquid crystal material is birefringent, light passing through one polarizing
filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer,
allowing it to pass through the second polarized filter. Half of the incident light is absorbed
by the first polarizing filter, but otherwise the entire assembly is transparent.
When a voltage is applied across the electrodes, a torque acts to align the liquid
crystal molecules parallel to the electric field, distorting the helical structure (this is resisted
by elastic forces since the molecules are constrained at the surfaces). This reduces the
rotation of the polarization of the incident light, and the device appears gray. If the applied
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voltage is large enough, the liquid crystal molecules in the center of the layer are almost
completely untwisted and the polarization of the incident light is not rotated as it passes
through the liquid crystal layer. This light will then be mainly polarized perpendicular to the
second filter, and thus be blocked and the pixel will appear black. By controlling the voltage
applied across the liquid crystal layer in each pixel, light can be allowed to pass through in
varying amounts thus constituting different levels of gray.
LCD USED:
In this project we are making use of 20 character X 40 line LCD module with LED
backlight DMC20481
BLOCK DIAGRAM
FIG: BLOCK DIAGRAM OF LCD MODULE
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FEATURES:
Interface with 8-bit or 4-bit MPU is available. 192 kinds of alphabets, numerals, symbols and special characters can be displayed by
built-in character generator (ROM).
Other preferred characters can be displayed by character generator (RAM). Various functions of instruction are available by programming: Clear display cursor at home on/off cursor blink character Shift display shift cursor Read/write display data. Etc. Compact and light weight design which can be easily assembled in devices. Single power supply +5V drive (except for extended temp. type) Low power consumption.
PIN ASSIGNMENT:
Pin No. Symbol Level Function
1 Vss -
Power Supply
0V(GND)
2 Vcc - +5V
3 VEE - For LCD Drive
4 RS H/L
Register Select Signal
Register H : Data InputSelect L : Instruction Input
5 R/W H/L
H : Data Read (Module-MPU)
L : Data Write (Module-MPU)6 E H,H-L Enable Signal (No Pull-Up Resistor)
7 DB0 H/L
Data Bus Line
8 DB1 H/L
9 DB2 H/L
10 DB3 H/L
11 DB4 H/L
12 DB5 H/L
13 DB6 H/L
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TIMING CHART:
Item Standard Value Unit
Min. Typ. Max.
Enable Cycle Time 1000 - ns
Enable Pulse Width, High Level 450 - ns
Enable Rise and Decay Time - - 25 ns
Address Setup Time, RS, R/W-E 140 - ns
Data Delay Time - - 320 nsData Setup Time 195 - ns
Data Hold Time(Write Operation) 10 - ns
Data Hold Time(Read Operation) 20 - ns
Address Hold Time 10 - ns
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CHAPTER 4.
SOURCE CODE OF THE PROJECT
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#include
#include
#include
#include
#include
#define d P1#define EOC_c() while(intr==1)
sbit DQ=P2^0;
sbit rd=P3^3;
sbit wr=P3^4;
sbit intr=P3^5;
sbit Light=P3^6;
sbit fan=P3^7;
unsigned char Read_Temperature (void);
void LCD_integer(unsigned char n);unsigned char adc();
void h2a(unsigned char n);
void main(void)
{
unsigned char p,s=0;
unsigned char b;
InitSerial();
LCD_init();
d=0xff;
intr=1;
LCD_cmd(0x0c);
while(1)
{
b=adc();
LCD_cmd(0x01);
LCD_str("lgt intesity:");
serial_trans_str("lgt intnsty:");
LCD_cmd(0x8d);
h2a(b);
p=owTouchReset();if(p)
{
LCD_cmd(0xc0);
LCD_str("no sensor");
}
else
{
s=Read_Temperature();
s=s-3;
LCD_cmd(0xc0);LCD_str("TEMP:");
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serial_trans_str("TEMP:");
LCD_cmd(0xc5);
LCD_integer(s);
LCD_dis('c');
}
if(s>35){
LCD_cmd(0xc0);
LCD_str("Fan is on:");
fan=1;
}
else
{
LCD_cmd(0xc0);
LCD_str("Fan is off:");
fan=0;
}if(b>4)|(THV
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return TZ;
}
void LCD_integer(unsigned char n)
{
unsigned char z;unsigned char num[8];
unsigned char l;
l=0;
while(n>0)
{
z=n%10;
num[l++]=z;
n=n/10;
}
while(l-->0)
{LCD_dis(num[l]+48);
serial_trans(num[l]+48);
}
}
void delay( unsigned int z)
{
unsigned int i,j;
for(i=0;i
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t=t%10;
n=n%10;
LCD_dis(temp+48);
serial_trans(temp+48);
LCD_dis(t+48);
serial_trans(t+48);LCD_dis(n+48);
serial_trans(n+48);
}
}
unsigned char adc()
{
unsigned char a;
rd=1;
wr=0;delay(1);
wr=1;
while(intr==1);
rd=0;
a=d;
delay(1);
intr=1;
return a;
}
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CHAPTER 5
ADVANTAGES & APPLICATIONS
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5.0 ADVANTAGES OF USING A DATA ACQUISITION FOR
COLLECTING DATA:
A data acquisition is an attractive alternative to either a recorder or data acquisition
system in many applications. When compared to a recorder, data loggers have the ability to
accept a greater number of input channels, with better resolution and accuracy. Also, data
loggers usually have some form of on-board intelligence, which provides the user with
diverse capabilities. For example, raw data can be analyzed to give flow rates, differential
temperatures, and other interpreted data that otherwise would require manual analysis by the
operator.
The major difference between a data acquisition and a recorder, however, is the way
the data itself is stored, analyzed and recorded. A common recorder accepts an input, and
compares it to a full scale value. The pen arm is then deflected across the recording width, to
produce the appropriate ratio of the actual input to the full scale input.
For example, using a recorder with a 1 Volt full scale, an input of 0.5 Volts would
move the pen 0.5/1 or 50% of the distance across the recording width. In comparison, a data
logger accepts an input which is fed into an analog-to-digital converter prior to analysis and
storage. This method has advantages in accuracy and resolution, while only a recorder can
provide a truly continuous trend recording.
5.1 DATA LOGGING VERSUS DATA ACQUISITION:
The terms data logging and data acquisition are often used interchangeably. However,
in a historical context they are quite different. A data logger is a data acquisition
system, but a data acquisition system is not necessarily a data logger.
Data loggers typically have slower sample rates. A maximum sample rate of 1 Hz may beconsidered to be very fast for a data logger, yet very slow for a typical data acquisition
system.
Data loggers are implicitly stand-alone devices, while typical data acquisition system mustremain tethered to a computer to acquire data. This stand-alone aspect of data loggers implies
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on-board memory that is used to store acquired data. Sometimes this memory is very large to
accommodate many days, or even months, of unattended recording. This memory may be
battery-backed static random access memory, flash memory or EEPROM. Earlier data
loggers used magnetic tape punched paper tape, or directly viewable records such as strip
chart recorders.
Given the extended recording times of data loggers, they typically feature a time-and date-stamping mechanism to ensure that each recorded data value is associated with a date and
time of acquisition. As such, data loggers typically employ built-in real-time clocks whose
published drift can be an important consideration when choosing between data loggers.
Data logger range from simple single-channel input to complex multi-channel instruments.Typically, the simpler the device the less programming flexibility. Some more sophisticated
instruments allow for cross-channel computations and alarms based on predetermined
conditions. The newest of data loggers can serve web pages, allowing numerous people to
monitor a system remotely.
The unattended and remote nature of many data logger applications implies the need in someapplications to operate from a DC power source, such as battery. Solar power may be used to
supplement these power sources. These constraints have generally led the data logger industry
to ensure that the devices they market are extremely power efficient relative to computers. In
many cases they are required to operate in harsh environmental conditions where computers
will not function reliably.
This unattended nature also dictates that the data loggers must be extremely reliable. Sincethey may operate for long periods nonstop with little or no human supervision, and may be
installed in harsh or remote locations, it is imperative that so long as they have power, they
will not fail to log data for any reason. Manufacturers go to great length to ensure that the
devices can be depended on in these applications. As such data loggers are almost completely
immune to the problems that might affect a general-purpose computer in the same
application, such as program crashes and the instability of some operating systems.
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5.2 APPLICATIONS OF DATA ACQUISITION:
Unattended weather station recording (such as wind speed / direction, temperature, relativehumidity, solar radiation)
Unattended hydrographic recording (such as water level, water depth, water flow, water PH,water conductivity).
Unattended soil moisture level recording. Unattended gas pressure recording. Road traffic counting. Measure temperatures (humidity etc) of perishables during shipments.
Process monitoring for maintenance and troubleshooting applications Wild life research. Measure vibration handling (drop height) environment of distribution packaging. Tank level monitoring. Deformation monitoring of any object with geodetic or geotechnical sensors controlled by an
automatic deformation monitoring system.
Environmental monitoring.
Vehicle testing Monitoring of relay status in railway signaling. For science education enabling measurement, scientific investigation and an appreciation
of change.
Record trend data at regular intervals in veterinary vital signs monitoring
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CHAPTER 6.
CONCLUSION &
FUTURE DIRECTIONS
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CONCLUSION:
Data Acquisition is not limited for any particular application, it can be used any where
in a process industries with little modifications in software coding according to the
requirements. This concept not only ensures that our work will be usable in the future but
also provides the flexibility to adapt and extend, as needs change.
Basically, Data Acquisition is a stand alone device but we can even connect it to a PC
by using RS232.We can also use Agilent VEE Pro software which is a graphical
programming environment optimized for use with electronic instruments for providing the
lab view of the parameters measured using Data Acquisition
FUTURE DIRECTIONS:
Data Acquisition are changing more rapidly now than ever before. The original model
of a stand alone data logger is changing to one of a device that collects data but also has
access to wireless communications for alarming of events, automatic reporting of data and
remote control. Data Acquisition are beginning to serve web pages for current readings e-
mail their alarms and FTP their daily results into databases or direct to the users.
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BIBLIOGRAPHY
TEXT BOOKS REFERED:
1. AVR Microcontroller and Embedded Systems by ALI MAZIDI
2. ATMEL AVR microcontroller primer: programming and interfacing
3. AVR CONTROLLER Data sheets
4. Hand book for Digital ICs from Analogic Devices
WEBSITES VIEWED:
www.atmel.com www.beyondlogic.org www.dallassemiconductors.com www.maxim-ic.com www.alldatasheets.com www.howstuffworks.com www.digi.com www.wikipedia.com