Post on 05-Apr-2018
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MICROCONTROLLER
BASED MULTIPOINT
MONITORING SYSTEM
ByNikhil U. Bodhankar
Hrishikesh S. Salvekar
Piyush H. Patil
Modern Education Societys College of
Engineering, Pune University , India.
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Introduction
The problem:
Less number of Air conditioning units could be
monitored by a single PC.
Large Number of controllers introduce overloading.
Limited distance prohibits connection of devices with
long distance.
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Specifications:
Serial communication using RS 485 with distance up
to 1.1Km. Monitoring up to 64 units.
The 64 units are divided into 4 groups of 16 each.
Connectivity with PC using RS-232 serial port. Microcontroller used: ATMEL 89C52.
Memory: 62C256 CMOS static RAM for
intermediate data storage.
Flexible Scanning even for small number of
connected units to save time.
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RS 485
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AC Controller Unit
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Visual indication of values using 16X2 alphanumeric
type LCD with Backlight.
Required power supply is +5V.
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Block Diagram
PC
system
RS-232MICROCONTROLLER
89C52
MEMORY
BUFFER RS485
BUFFER RS485
BUFFER RS485
BUFFER RS485LCD
DECODER
TX
RX
E
CPU card
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Block Diagram Description:
Instead of using a dedicated PC for controlling and
monitoring large no. of application units, we haveimplemented a single unit named as a CPU card/Dataunit which will reside between the computer and theapplications.
Main functions to be carried out by the CPU card:- Selection of particular unit through decoder.
- Scanning I/Ps and storing data into memory.
- To Send the data stored in memory to the computerafter scan cycle.
- Display the data on LCD.
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Microcontroller 89C52 scans 64 units andcommunicates with the PC. this is achieved by serialcommunication.
RS-485 can support up to 32 nodes maximum.considering safety factors and after several tests wefound that max 20 nodes can be driven satisfactorily.
Thus we have divided the 64 units into 4 groups, each
having 16 nodes. Each control unit to be monitored is provided with a
Unique unit ID.
This ID can be changed from the AC controller unit.
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Information of each unit is stored in a file of size 122
byte.
Microcontroller receives the information from eachunit and stores it into RAM IC62256.
Once all the 64 units are scanned the total file of size
122 X 64 is sent to the PC on RS-232 port.
The decoder (IC74138) is used to select the group of
control units like 0-15,16-31,32-44,45-63. It gives
signal to buffer for selection of group.
Since it is a decoder only one line will be selected at atime which will not be the case if port pin of 89C52
were used directly.
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Buffer(IC74244) serves purpose of isolation and
selection of particular group.
The received data will show various parameters likeblower, heater and compressor run hours and Faults if
present. These parameters are displayed on
alphanumeric LCD display.
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Microcontroller 89C52
The major functions of microcontroller are
- Serial communication with the application devices.
- Storing the collected data into RAM.
- Displaying the data on LCD. Features:
- 8-bit microcontroller.
- 8 Kb of In-system Reprogrammable Flash memory.
- Endurance: 1000 Write/Erase Cycles.
- Fully Static operation: 0Hz to 24 MHz.
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- Three-level program memory clock.
- 256 x 8 bit internal RAM.
- 32 Programmable I/O lines.
- Three 16 bit Timers/counters.
- 8 Interrupt Sources.
- Programmable serial channel.- Low Power Idle and power down modes.
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Communication standards
RS 485- Supports 32 drivers and
32 receivers
- Can be connected in a 2wire or 4 wire mode
- Typical use is a singlePC connected to severaladdressable devices that
share the same cable
RS 232- supports one driver and
one receiver
- Signals are representedby voltage levels withrespect to systemcommon ground
- Typical use for point to
point communication atlow data transmissionrates.
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Components
Optocouplers: MCT6,MCT2E
MAX-232
RS-485
RAM 62256
Decoder 74138
Buffer 74244
Latch 74373
Bidirectional Transcreceiver 75176
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Flow Charts
Send data
Start
Initialize serial port settings
Transfer data
End
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START
Initialize serial port settings
Send request to receive data
Start receiving the data
If data is received
i.e. if unit is
present
Receive=true
If received
bytes==122
&&
Received = true
Display the data
End
Incrementing
timer count
If timer
count is
timeout
End
NO
NO
NO
YES
YES
YES
Receive data
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Future Enhancements
Development of software on PC side, i.e. it
will give various details of parameters which
have been monitored, directly on the screen of
PC.
The software for controlling the parameters
through PC.
User interface of CPU card through SMS,
email after a fixed time interval.