data format error with serial communication

Hello everybody, i have realized a script who send some comands to a serial devide. The device is a Mitsubishi Rv-m1 robot and it communicates with matlab on RS232. Here is the script.

%%Inizializzazione 
clear all 
clc 
delete(instrfind)
cam = webcam('Trust Webcam');
s = serial('COM4');
s.StopBits = 2;
s.Parity = 'even';
s.DataBits = 7;
s.BaudRate = 9600;
fopen(s);
t2 = timer('TimerFcn', 'stat=false; disp(''Timer'')','StartDelay',2);
t5 = timer('TimerFcn', 'stat=false; disp(''Timer'')','StartDelay',5);
t8 = timer('TimerFcn', 'stat=false; disp(''Timer'')','StartDelay',8);
fprintf(s,'SP 5');
fprintf(s, 'NT');
pause

%%Definizione posizioni
% Posizione webcam
fprintf(s,'PD 1,+32.5,+250.3,+318.4,-93.8,+179.9');
start(t2)
waitfor(t2)
% Origine piano dei cilindri
fprintf(s,'PD 2,-122.4,+365.8,+33.8,-86.8,+179.9');
start(t2)
% Vettore contenente le coordinate dell'origine
origin = [-122.4 365.8 33.8 -86.8 179.9];
waitfor(t2)

%%Posizionamento per scattare la foto 
fprintf(s,'MO 1');

%%Snapshot - ridimensionamento - localizzazione posizioni
new_circle_recognition;

%%Posizionamento nell'origine
fprintf(s,'MO 2');

%%Movimento dall'origine alla posizione dell'oggetto 

% Vettore contenente le coordinate del centro del cilindro
% Ottenuto modificando il vettore origin con le coordinate dei centri. 
cylinder = [origin(1)+centrimm(1),origin(2)-centrimm(2),origin(3),origin(4),origin(5)];
% Conversione in formato char con 2 cifre decimali
movechar = sprintf('MP %0.1f,%0.1f,%0.1f,%0.1f,%0.1f',cylinder(1),cylinder(2),cylinder(3),cylinder(4),cylinder(5));
% Conversione in formato adatto per il comando seriale
% Esempio di comando : 'MP +28.1,311.9,40,-88.8,179.9'
movestr = cellstr(movechar);
% Movimento robot
fprintf(s,movestr);

In the first section i have setted all the correct parameters for the communication infact the firsts commands (fprintf(s,'SP 5'); fprintf(s, 'NT'); fprintf(s,'PD 1,+32.5,+250.3,+318.4,-93.8,+179.9');) work correctly. "new_circle_recognition" is a script who makes a snapshot of the webcam (matlab object cam) and returns a vector 1x2 named centrimm with the position in mm of the center of a cylindric object. I want to use the information inside centrimm for send a serial command to serial object "s" with fprintf. The string should be like this: 'MP +28,311,40,-88,179' so i have used sprintf for create a char variable with the number in float format without decimal digits.

If i use char variable "movechar" in fprintf

fprintf(s,'movechar')

the device returns an error sound instead using cell variable "movestr"

fprintf(s,movestr)

matlab returns "cmd must be a string".

At this time i don't have at home the robot. I believe the problem is in the wrong data format of the command sent with fprintf. I'm thinking to use something like this

fprintf(s,'%s',movestr)

or i can use fwrite instead fprintf. does someone have a suggestion? Thanks a lot guys.

Answer 1

[Walter Roberson]

fprintf(s, '%s\n', movestr{:});

[squall141]

Sorry for the incompetence, but why '%s\n'? In the first part i didn't need to use this and all work. Furthermore using movestr{:} i obtain again a char variable and in this format the device gives an error. Does '%s\n' do the conversion in the correct format?

Sorry for the annoyance

[Walter Roberson]

fprintf(s,'movechar') returns an error because you were literally sending the word movechar rather than the content of the variable movechar

fprintf(s,movestr) was giving you an error because you had taken the character vector you had created and you were using movestr = cellstr(movechar); for no obvious reason, which turned the single string into a cell array of strings, which fprintf() cannot deal with directly.

You used

movechar = sprintf('MP %0.1f,%0.1f,%0.1f,%0.1f,%0.1f',cylinder(1),cylinder(2),cylinder(3),cylinder(4),cylinder(5));

Notice that you do not end the line of text with \r or \n . It so happens that if you are using a serial device and you use

fprintf(s, 'some constant string')

then that is equivalent to

fprintf(s, '%s\n', 'some constant string')

which adds the configured end-of-line delimiter at the end of the string, which is why you might not have noticed the lack of newline before; see https://www.mathworks.com/help/matlab/ref/serial.fprintf.html

fprintf(obj,'cmd') writes the string cmd to the device connected to the serial port object, obj. The default format is %s\n

My suggested code

fprintf(s, '%s\n', movestr{:});

uses that format once for every string in the cell array of strings in movestr . It is equivalent to

fprintf(s, '%s\n', movestr{1}, movestr{2}, movestr{3}, ... movestr{end});

which in turn would be equivalent to

fprintf(s, '%s\n', movestr{1});
fprintf(s, '%s\n', movestr{2});
...
fprintf(s, '%s\n', movestr{end});

except for some details about when flushing occurs. The short form for that would be

fprintf(s, movestr{1});
fprintf(s, movestr{2});
...
fprintf(s, movestr{end});

I do not know why you used

movestr = cellstr(movechar);

so I speculated that you were showing a simplified form of the code where you might, in your real code, want to store multiple strings and send them all at once.

But for the code you show... the easiest repair is to just remove the line

movestr = cellstr(movechar);

and continue to use

fprintf(s, movestr);

[squall141]

I have used cellstr to obtain a value which includes character '. In this way I have 'my generic string' instead my generic string. If I remove

movestr = cellstr(movechar);

I have only movechar which is an 1xn char like this

movechar =

MP 12.5,52.7,256.3,659.4,179.5

Furthermore in your answer you say to use

fprintf(s, '%s\n', movestr{:});

on movestr 1x1 cell obtained with cellstr (that you suggest to remove). Anyway i can't use movestr{2}, movestr{3} etc because it's only 1x1 cell. Only movestr{1} and movestr{:} works obviously.

[Walter Roberson]

The inclusion of the ' is only for display purposes in cell strings; it is not stored along with the string. If you need to actually transfer ' (which I doubt) then you should

fprintf(s, '''%s''\n', movestr)

where movestr is not a cellstr

movestr{2} would be beyond movestr{end} in the case of a 1 x 1 cellstr. I am illustrating what cell array expansion means.