آموزش نحوه ارتباط سریال برد Arduinoبا نرم افزار Matlab و ارسال داده همراه با کد برنامه

Serial Communication between Arduino and
MATLAB

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Serial Communication between Arduino and
MATLAB

ByAman Mangal
IIT Bombay
June 6, 2012

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Prerequisite

Serial data transfer in Arduino. Follow the link to learn more-1 http://arduino.cc/en/Reference/serial
2 http://www.ladyada.net/learn/arduino/lesson4.html
MATLAB programming. To learn more, go to-1 http://users.ece.gatech.edu/bonnie/book/TUTORIAL/
tut_1.html
2 http://www.mathworks.in/help/techdoc/matlab_
product_page.html

You should be familiar with MATLAB structures, MATLAB
objects etc.
Basic programming concepts
.
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Serial Communication

Serial means ”One after another”.
Serial communication is when we transfer data one bit at a
time, one right after the other.
Information is passed back & forth between the computer and
Arduino by, essentially, setting a pin high or low.
Just like we turn an LED on and off, we can also send data.
One side sets the pin and the other reads it.
MATLAB can read/send the data from/to the serial port of
the computer and process it.
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Buffer
It is most important to understand the nature of buffer to
avoid errors later while writing codes.
There exists a buffer between the two events of sending and
reading the data.
Say a sensor is streaming back data to your program, more
frequently than your program reads it.
Then the data is stored to a list which we call a buffer.
One writes data into it and other reads it, may be with
different speeds.
Buffer are of finite length.
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Buffer...in detail
Initially the buffer is empty.
As new data values come in they get added to the bottom of
the list (most recent data).
If your program reads a value from the buffer, it starts at the
top of the list (oldest data).
Once you read a byte of data, it is no longer in the buffer.
The data in the second position on the list moves up to the
top position
As soon as the buffer is full and more data is sent, the oldest
data gets discarded to make space for new data.
You have to be smart enough not to loose data.
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Buffer...example
We set up the Serial communication between arduino and PC
with a buffer length of 5.
1
2
3
4
5
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Buffer...example
The value 10 and 6 are transferred respectively.
1 10
2 6
3
4
5
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Buffer...example
One value is read. The value 10 is the oldest. So it will be
read first.
1 6
2
3
4
5
Note that 10 no longer exists in the buffer.
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Buffer...example
Now, assume that the buffer is full.
1 6
2 4
3 5
4 9
5 3
What will happen if we write one more data value, say 12, to
the buffer?
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Buffer...example
The buffer will look like as follows-1 4
2 5
3 9
4 3
5 12
Note that the oldest data ”6” is discarded.
All the data is shifted up and new value is added as the last
entry to the buffer.
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Before we continue...
We have to connect the Arduino board to the PC.
Each serial port on the PC is labeled COM1, COM2 etc.
The Arduino will be given a COM Port Number. You should
figure it out by following these steps-1 Right click on ”My Computer icon” and select Manage.
2 Select Device Manager in the tree view you will see on the
left side in the new window opened.
3 Find and select Ports(COM& LPT) in the center panel.
4 There, you will find lists of all the ports attached to your
computer.
5
Figure out the one you are concerned with. Refresh the
window if you don’t find any!
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Almost ready...
Now we are ready for the MATLAB and Arduino serial
communication.
We will only focus upon the MATLAB. We will study how can
we set up serial port objects, send and read data from the
buffer in MATLAB.
I assume the you already know how to send/read data in
Arduino.
Follow the link given in the beginning of the tutorial if you
wish to learn Serial Communication in Arduino.
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Styles used throughout the tutorial
All the MATLAB commands are written in italics and
preceded by >>
The MATLAB output is written in blue color everywhere.
Use
>> help ’command’
>> doc ’help text’
to get help in MATLAB for any command used in the tutorial.
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Setting up Serial Port Object
We first need to create a serial port object.
Serial port object is just a name given to that serial port so
that we can use it in later commands.
>> s = serial (’COM1’);
Serial Port Object : Serial-COM1
Communication Settings
Port: COM1
BaudRate: 9600
Terminator: ’LF’
Communication State
Status: closed
RecordStatus: off
Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 0
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Setting up Serial Port Object
This line of command only constructs the object. It does not
check/setup/initialize the communication.
This command will still work even if the serial port is not
connected to any device.
Many objects can be created for a serial port but only one can
be connected at a time.(we will see later)
This shows all the property of the constructed serial port
object.
In MATLAB, s is a structure which has all the above
properties. We can access/modify them using dot(.) operator.
Note that the Status is closed. It implies that the serial port
is not connected.
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BaudRate
It is the rate of transfer of the data in bits/sec.
We can change the BaudRate using the set method as
follows->> set(s, ’BaudRate’, 4800);
>> s.BaudRate = 4800 ;
You can also setup different BaudRate while making the serial
port object as follows->> s = serial(’COM1’,’BaudRate’, 4800);
You can verify the change using get method->> get(s, ’BaudRate’)
ans = 4800
The following will also show the similar result->> s.BaudRate
ans = 4800
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BaudRate
You can also do the following to verify the change->> s
Serial Port Object : Serial-COM1
Communication Settings
Port: COM1
BaudRate: 4800
Terminator: ’LF’
Communication State
Status: closed
RecordStatus: off
Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 0
Note the new value of BaudRate shown.
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Properties of Serial port object
As we have already stated that s is of MATLAB datatype
called structure(similar to structures in C++).
There are lots of flexibility MATLAB provides to change the
properties of the serial port object.
The commands are similar to what we have used for
BaudRate.
Use following command to list down all these properties and
their current value->> get(s)
To see the possible values of all these properties, use->> set(s)
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Setup the connection
Before you actually write the data to the serial port, you must
connect to device.
This is like a JAVA lock. Only one entity can acquire the lock
at a time.
Use fopen to acquire the lock and setup the connection.
>> fopen(s)
Notice the status property of the serial port object->> s.Status
ans = open
If the lock is already acquired, fopen will give an error.
To avoid error, first check the Status property of the serial
port object. If it is closed then try to setup the connection.
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Writing to the Serial Port in MATLAB
MATLAB can write any kind of data to the serial port binary,
string, int, float etc. with specified precision.
We use fwrite or fprintf to write data.
Transfer an int/float array->> fwrite(s, vector array, ’precision’);
The precision specifies the datatype of the vector array. It can
be ’int8’, ’int16’, ’float32’, ’float64’, ’uint8’, ’char’ etc.
String->> fwrite(s, ’string’);
You can use fprintf for strings as well->> fprintf(s, ’string’);
You can specify the format in fprintf for a string.
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Reading from Serial Port in Arduino
You can follow these steps to read data in ArduinoYou can choose the kind of data you are expecting, otherwise
byte dataype can be used.
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Writing to Serial Port in Arduino
Use following function to write data in Arduino to the Serial
Port.
Note the use of println not print.
This will be helpful when we will read the data in MATLAB.
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Reading from Serial Port in MATLAB
fscanf is used to read the data->> data = fscanf(s);
This will read all the data until it finds a new line/Terminator.
That is why we used println instead of print.
By following this procedure you will be reading all the data
sent in one command of Serial.println at a time.
In this case, MATLAB automatically converts data into the
correct format and stores into the MATLAB variable.
If there is no data to read, a time out will occur.
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Reading from Serial Port in MATLAB
To avoid time out, you can first check the BytesAvailable
property of serial port object just like we did in Arduino->> if s.BytesAvailable > 0
data = fscanf(s);
end
You can specify the size of the data you want to read in case
you use Serial.print.
You have to specify the format of data together with the size
of the data.
>> fscanf(s, ’format’, size);
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fread in MATLAB
You can also use fread instead of fscanf to read the data
from serial port.
fread reads until the Terminator is seen.
>> data = fread(s)
fread doesn’t convert the data in the correct format until you
specify it.
It is better to specify size while using fread.
You also have to specify precision in fread if you want to
specify size.
>> data = fread(s, size, ’precision’)
Try using fwrite & fscanf for writing and reading the data.
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Format
Format is basically C conversion specification language.
The following formats can be usedAman Mangal, IIT Bombay Serial Communication between Arduino and MATLAB 26/36


Size
There are 2 waysThe filling in the matrix takes place columnwise. The first
column is filled, then 2
nd
column and so on.
This will keep reading until the vector/matrix of the given size
is created.
Time out will occur if the available data is not enough to fill
the whole vector/matrix.
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BufferSize
It is very important not to loose the data while the data gets
transferred.
As mentioned before, the data gets discarded if the Buffer is
full to accommodate new data.
To avoid loosing data, specify almost equal Baudrates in both
the sytem MATLAB & Arduino.
We have already seen how we can control the BaudRate.
We can specify the BufferSize in MATLAB according to the
need of program using following methodsset(s, ’BufferSize’, 1024) %in bytes
s.BufferSize = 1024; %in bytes
(Similar to BaudRate)
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Read/Write State
Each time you transfer the data, it is either receive or sent by
MALTAB.
The ValuesSent & ValuesReceived properties of serial port
object shows these values.
You can always check these values to ensure the correct
amount to data transferred.
You can also optimize your program to use the least possible
size datatype for the data to be transferred.
We have already seen the BytesAvailable property.
TransferStatus shows whether the data transfer is complete.
fprintf blocks the command line to execute other commands
while the data is getting transferred while fwrite doesn’t.
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End the Connection
This is very important step while Serial Communication.
Make sure the execution of this step even in case the data is
not transferred.
Use fclose to end the connection->> fclose(s)
Delete the serial port object if you are done with
communication.
>> delete(s)
>> clear s
So if fopen is executed then fclose must be executed anyhow
otherwise it will create problem when you use it next time.
You should use try-catch statement to ensure that the serial
port is closed before the program ends execution.
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To remember
You cannot simultaneously view the data in MATLAB and
Arduino serial port because the data can only be read once.
The data is removed as soon as it is read first time.
The synchronisation of data transfer is very important while
communication.
Always check for the property before setting its new value.
For example before you use fopen, check whether the serial
port is already used.
Check the BytesAvailable property before you read the data
in MATLAB.
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To remember
Be selective while you choose the datatype of the data. It will
affect the time taken in communication.
Choose an optimum BufferSize.
Always close the connection in the end so that we can use the
port next time.
Close the connection in MATLAB before you upload your
code to Arduino.
Whenever you setup a new connection, it flushes all the data
sent/received earlier.
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INSTRFIND
The function instrfind finds all the possible, existing serial
port objects.
It returns an array of serial port object.
>> h = instrfind
Instrument Object Array
Index: Type: Status: Name:
1 serial closed Serial-COM8
2 serial closed Serial-COM8
3 serial closed Serial-COM1
You can access any of the object using index like h(2)
>> s = h(2);
Now s is similar serial port object which we created in the
beginning of the tutorial.
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INSTRFIND....advanced
You can specify the properties of the serial port object you
want to search for->> out1 = instrfind(’Port’,’COM1’);
>> out2 = instrfind(’Port’,’BaudRate’,’COM2’,4800);
Note that instrfind returns array/vector of serial port object.
It is used when you want to retrieve a deleted serial port
object.
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More to come
We have learnt all the basics of Serial Communication in
MATLAB.
We can extend this knowledge to make a real time serial
communication system.
You can make a system which reads the data from a digital pin
of Arduino and transfers all the data to MATLAB in real time.
Plot the received data on the graph in MATLAB.
The pin number may be specified by the user in MATLAB.
I will present the solution of the problem after a week.
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Thank you
Thanks for your patience while reading the tutorial.
I hope you find it useful.
Use MATLAB help to know more about anything we have
learnt here.
Contact me for any query: [e-mail]
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