How can I read multiple sensors through the serial?

I want to read 3 thermocouple sensor from my Arduino which is connected through serial port. I have succecssfully read the 3 temperature but the result is combine in only 1 graph. So how to make it display in 3 graph for each the sensor.

Matlab Code:

clear all
s = serial('COM4');
fopen(s);

i=1;
while(1)
    
    data(i) = str2double(fscanf(s));
    plot(data);
    pause(0.1);
    i=i+1;
    
end

Arduino Code:

#include "max6675.h" // max6675.h file is part of the library

//thermocouple 1
int so1Pin = 4;// SO1 = Serial Out
int cs1Pin = 5;// CS1 = chip select CS pin
int sck1Pin = 6;// SCK1 = Serial Clock pin

//thermocouple 2
int so2Pin = 8;// SO1 = Serial Out
int cs2Pin = 9;// CS1 = chip select CS pin
int sck2Pin = 10;// SCK1 = Serial Clock pin

//thermocouple 3
int so3Pin = 11;// SO1 = Serial Out
int cs3Pin = 12;// CS1 = chip select CS pin
int sck3Pin = 13;// SCK1 = Serial Clock pin

MAX6675 temp1 (sck1Pin, cs1Pin, so1Pin);// create instance object of MAX6675
MAX6675 temp2 (sck2Pin, cs2Pin, so2Pin);// create instance object of MAX6675
MAX6675 temp3 (sck3Pin, cs3Pin, so3Pin);// create instance object of MAX6675

void setup() {

          
  Serial.begin(9600);// initialize serial monitor with 9600 baud
  //Serial.println("MAX6675"); 

}

void loop() {
  // basic readout test, just print the current temp
  // MAX6675 Temperature reading on Serial monitor
   Serial.print(""); 
   Serial.println(temp1.readCelsius());// Read temperature in Degree Celcius unit    
   delay(100);// Update interval is 1 sec

   Serial.print(""); 
   Serial.println(temp2.readCelsius());// Read temperature in Degree Celcius unit    
   delay(100);// Update interval is 1 sec

   Serial.print(""); 
   Serial.println(temp3.readCelsius());// Read temperature in Degree Celcius unit    
   delay(100);// Update interval is 1 sec
}

Answer 1

[Walter Roberson]

clear all
s = serial('COM4');
fopen(s);

ah(1) = animatedLine('Color','k');
ah(2) = animatedLine('Color','b');
ah(3) = animatedLine('Color','g');

starttime = tic;
while true
    
    data = fscanf(s, '%f%f%f');
    if length(data) < 3
      fprintf('Data shortage, stopping\n');
      break;
    end
    
    curtime = toc(starttime);
    addpoint(ah(1), curtime, data(1));
    addpoint(ah(2), curtime, data(2));
    addpoint(ah(30, curtime, data(3));
    pause(0.1);
end

with

#include "max6675.h" // max6675.h file is part of the library

//thermocouple 1
int so1Pin = 4;// SO1 = Serial Out
int cs1Pin = 5;// CS1 = chip select CS pin
int sck1Pin = 6;// SCK1 = Serial Clock pin

//thermocouple 2
int so2Pin = 8;// SO1 = Serial Out
int cs2Pin = 9;// CS1 = chip select CS pin
int sck2Pin = 10;// SCK1 = Serial Clock pin

//thermocouple 3
int so3Pin = 11;// SO1 = Serial Out
int cs3Pin = 12;// CS1 = chip select CS pin
int sck3Pin = 13;// SCK1 = Serial Clock pin

MAX6675 temp1 (sck1Pin, cs1Pin, so1Pin);// create instance object of MAX6675
MAX6675 temp2 (sck2Pin, cs2Pin, so2Pin);// create instance object of MAX6675
MAX6675 temp3 (sck3Pin, cs3Pin, so3Pin);// create instance object of MAX6675

void setup() {

          
  Serial.begin(9600);// initialize serial monitor with 9600 baud
  //Serial.println("MAX6675"); 

}

void loop() {
  // basic readout test, just print the current temp
  // MAX6675 Temperature reading on Serial monitor 
   Serial.print(temp1.readCelsius());// Read temperature in Degree Celcius unit    

   Serial.print(" "); 

   Serial.print(temp2.readCelsius());// Read temperature in Degree Celcius unit    

   Serial.print(" "); 

   Serial.println(temp3.readCelsius());// Read temperature in Degree Celcius unit
   
   delay(100);// Update interval is 1 sec
}

Notice that you (probably) only need one delay of 100 for all three sensors together

The timing I do for the X axis could be improved: you could have the arduino keep track of its timing and send that information along with the temperatures, so that what you were plotting was the time of collection rather than the time MATLAB collected the data.

I would even say that you should change the

    pause(0.1);

to just

   drawnow();

and let MATLAB just sit at the fscanf() until it got data from the arduino -- less risk of the delays on the two sides getting badly ouf of synchronization.

[Nazmi Rosly]

Im getting this error:

Error using tic

Too many input arguments.

Error in splitoooo (line 16)

curtime = tic(starttime);

[Walter Roberson]

Yes, sorry, that should be a call to toc() instead of tic()

[Nazmi Rosly]

okay I got it. Thank you very much

[Nazmi Rosly]

Can I use this code to send the data to thingspeak? I have tried using this command :

thingSpeakWrite(1477635,{data(1),data(2),data(3)},'WriteKey','FG0W2NDFPSS8CEP0')

the error:

Warning: Unsuccessful read: A timeout occurred before the Terminator was reached.

'serial' unable to read any data. For more information on possible reasons, see Serial Read Warnings.

Data shortage, stopping

[Walter Roberson]

Unfortunately I have not used ThingSpeak .

Are you getting that serial error even when you do not attempt to write to ThingSpeak ?

[Nazmi Rosly]

your code is working well, but there is a little bit typo for animatedLine which should be animatedline and addpoint should be addpoints. btw thank you.

[Walter Roberson]

You are right. And the strange thing is that I checked both of those names when I was posting, and managed to post the wrong way for both of them.

[Nazmi Rosly]

It's okay since all the error can be fixed just by google the error. One more thing that I want to ask is can we save all the data in the workspace?

[Walter Roberson]

You can store the values as they are received; the difficulty is in storing them efficiently . It is not advisable to fwrite() each set of points as it is received, and it is not advisable to extend arrays as each set of points is received.

animatedline() deals with the situation internally by having fixed-length buffers (5000 points by default) and keeping track of the position within the current buffer; when a buffer fills, then it adds on a new buffer -- but it only has to move pointers to do that, rather than copying data each time.

It is possible to get all of the point locations after the loop is terminated (which happens in the code I posted when a data read fails.) Using ah(1), ah(2), ah(3) as the handles to the animatedlines, then

ah(1).SegmentContainer.Children

is an object array that you can treat as a struct array. The fields to look at are XData, YData, ZData.

ah(1).NumPointsAdded

is the total over all segments (buffers). Remember that the last segment will probably not be full, so use

mod(ah(1).NumPointsAdded-1, ah(1).SegmentSize) + 1

to calculate the number of points actually used in the last segment.