How to sending data from matlab to arduino?

I tried to learned some basic a sending data from matlab to arduino with a LED. i tried to turn on and off the LED if i changed some value in matlab. but the result that the LED is gived was always same. please help me to correct. my MATLAB code is

arduino=serial('COM3','BaudRate',9600); % create serial communication object on port COM3 
fopen(arduino); % initiate arduino communication
answer = 0.2
fprintf(arduino,%f%,answer); % send answer to arduino
fclose(arduino); % end communication with arduino

and my arduino code is

 int ledPin=13;
    int matlabdata;

    void setup()
    {
    pinMode(ledPin,OUTPUT);
    Serial.begin(9600);
    }

    void loop()
    {
    if(Serial.available()>0) // if there is data to read
    {
    matlabdata=Serial.read(); // read data
    if(matlabdata<0.2)
    digitalWrite(ledPin,HIGH); // turn light on
    else if(matlabdata>0.2)
    digitalWrite(ledPin,LOW); // turn light off
    }
    }

[Yusof Zainol Abidin]

did you manage to get the answer?? im having the same problem.. please help me..

Answer 1

[Thang Pham]

I think the answer for your problem is: Serial.read() reads a 1-byte char-type data from the serial communication, while your sent data from MATLAB is a float-type data.

To solve this problem:

either change your sent data to char type (use fprintf(arduino, '%s', char(2)))

or change your sent data to string type and change your receive method in Arduino so that your program can read a string "0.2" and then convert it to respective float number. See: https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/tofloat/ for converting string to float and https://www.arduino.cc/reference/en/language/functions/communication/serial/readstring/ for string reading.

Hope it could help you.

[Walter Roberson]

fprintf(arduino,'%f\n',answer); % send answer to arduino

would send convert the numeric value in answer to character representation and send it, followed by newneline. Serial.ParseFloat() can then read the number; https://www.arduino.cc/reference/en/language/functions/communication/serial/parsefloat/