microcontroller based multims

7/31/2019 Microcontroller Based MultiMS

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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.

microcontroller based multims

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