Serial comm matlab

Serial Communication between Arduino and
MATLAB
By-
Aman Mangal
IIT Bombay
June 6, 2012
Aman Mangal, IIT Bombay Serial Communication between Arduino and MATLAB 1/36

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.

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 o, 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.

Buer
It is most important to understand the nature of buer to
avoid errors later while writing codes.
There exists a buer 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 buer.
One writes data into it and other reads it, may be with
dierent speeds.
Buer are of

nite length.

Buer...in detail
Initially the buer 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 buer, it starts at the
top of the list (oldest data).
Once you read a byte of data, it is no longer in the buer.
The data in the second position on the list moves up to the
top position
As soon as the buer 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.

Buer...example
We set up the Serial communication between arduino and PC
with a buer length of 5.
1
2
3
4
5

Buer...example
The value 10 and 6 are transferred respectively.
1 10
2 6
3
4
5

Buer...example
One value is read. The value 10 is the oldest. So it will be
read

rst.
1 6
2
3
4
5
Note that 10 no longer exists in the buer.

Buer...example
Now, assume that the buer 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 buer?

Buer...example
The buer 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 buer.

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

gure 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

nd 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

nd any!

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
buer 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.

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.

Setting up Serial Port Object
We

rst 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: o
Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 0

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.

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 dierent 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

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: o
Read/Write State
TransferStatus: idle
BytesAvailable: 0
ValuesReceived: 0
ValuesSent: 0
Note the new value of BaudRate shown.

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
exibility 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)

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,

rst check the Status property of the serial
port object. If it is closed then try to setup the connection.

Writing to the Serial Port in MATLAB
MATLAB can write any kind of data to the serial port binary,
string, int,
oat etc. with speci

ed precision.
We use fwrite or fprintf to write data.
Transfer an int/
oat array-
fwrite(s, vector array, 'precision');
The precision speci

es the datatype of the vector array. It can
be 'int8', 'int16', '
oat32', '
oat64', '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.

Reading from Serial Port in Arduino
You can follow these steps to read data in Arduino-
You can choose the kind of data you are expecting, otherwise
byte dataype can be used.

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.

Reading from Serial Port in MATLAB
fscanf is used to read the data-
data = fscanf(s);
This will read all the data until it

nds 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.

Reading from Serial Port in MATLAB
To avoid time out, you can

rst 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);

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.

Serial comm matlab

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