Reading ADC data from MSP430 to Matlab via serial port

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Hiril Patel 2022-6-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1741405-reading-adc-data-from-msp430-to-matlab-via-serial-port

编辑： Walter Roberson 2024-7-17

My situation is

1. external ADC samples from one channel and transmit to Serial port Via Uart and then switches over to second channel to do same and then third.

2. I manage to view data in Hterm and it looked quite fine.

3. I want to plot it live in matlab- I know there are ways to do it but can someone here explain me a basic step by step to achieve my objective?

I have basic idea of what i should be doing

setup serial communication.
create array to store uart values
calculate voltage values
plot live values

It would be nice if someone points out me for where to look for point 2 and 4 specifically.

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Walter Roberson 2022-6-18

编辑：Walter Roberson 2024-7-17

You have binary, and it looks like you have a different number of bytes at times. You just might be sending a space after each / but that is not clear. If that is / space then it is generally followed by 8 bytes. But sometimes it is only 7 and sometimes it is 9.

You should switch to one of the following schemes:

Write numbers in character form, either decimal or hexadecimal, with non-number between the entries. Either put newline after each individual number or put newline at the end of a group of samples; or
Write numbers in binary using a fixed number of bytes per entry, so that you can ask to read a fixed number of bytes with no delimiter; or
At the beginning of each burst of numbers, write a byte (or two) which is the number of bytes that follow in that packet, with no end of line. The input side reads the size (fixed size) and uses the size to read that many bytes; or
use a variable length binary stream with a fixed termination byte, with the binary stream having been carefully adjusted so that it never accidentally includes the termination character. For example you might use newline, and everywhere that newline would have been sent as data send 255 0 and everything 255 would have been sent, send 255 255.

Walter Roberson 2022-6-23

在 MATLAB Online 中打开

Look at https://www.mathworks.com/matlabcentral/answers/uploaded_files/1036145/Capture.JPG in your display of the input data. That's the one that starts

ÿ ֋ù/

Those are binary not character.

You have two choices:

you can continue to send in binary, and do binary reads using fread() (for serial) or read() (for serialport). If you are not always sending the same number of bytes or if not everything is the same binary data type, then you may need to add some extra bytes to indicate how the following data is to be treated. If you use this fread() binary approach, you do not put any delimiters between values and you do not send newline; OR
you can switch to sending the numbers as text. If you send as text, put a space between the values and put newline at the end of the line. On the MATLAB end, fscanf() will read the entire line of values, returning a numeric vector.

You only need things like your /A/ or similar if you are sending the channels in inconsistent order. For example if you had a series of devices that generated interrupts when it was ready, and you wanted to send the data in the order received, then there might be reason to tag each value according to the channel it is associated with.

Hiril Patel 2022-6-30

在 MATLAB Online 中打开

Hello again Walter,

can you suggest me what to do with following case, as it is associated with the previous system:

i managed to get those values in matlab and working with calculation but here I am solving Mohr's circle formulas and thus I have three equation and three variables( i studied about syms and solve functions and feature but still have some error which I am not able to figure out). Perhaps I am not converting those variables to appropriate data type( I have little to no idea whats going on behind them, here is the script and a sample of data type :

ch0, ch1, ch2 are csv file i imported generated from python

clc;
clear;
% ADC and strain gauge settings
vref = 3300;                % ADC reference millivolts
ADC_resolution = 8388607;   % 2^23 24bit of resolution
A = 4;                      % if fsr = +/-2 
pga = 1;                    % ADS1220 amplifier gain setting
E = 3.3;                    % Bridge excitation voltage
K = 2.04;                   % Gauge factor
% Importing adc values
ch0 = readmatrix('ch0.csv');    
ch1 = readmatrix('ch1.csv');
ch2 = readmatrix('ch2.csv');
% Conversion to proportional millivoltage
n = vref/ADC_resolution;
Channel0 = n*ch0;
Channel1 = n*ch1;
Channel2 = n*ch2;
% Strain calculation
gauge0 = (4/2.04)*(Channel0/E);
gauge1 = (4/2.04)*(Channel1/E);
gauge2 = (4/2.04)*(Channel2/E);
% Calculation of unblanced bridge in nonstrained state:
% Vr = (bridge strained output - bridge unstrained output)/excitation voltage
% Measured strain to principle strain conversion
    % Maximum principal strain
    syms e_x e_y lamda_xy
    eq0 = (gauge0 - (e_x*((cos(0)).^2)) +(e_y*((sin(0)).^2)) + (lamda_xy*(sin(0))*(cos(0))));
    eq1 = (gauge1 - (e_x*((cos(60)).^2)) +(e_y*((sin(60)).^2)) + (lamda_xy*(sin(60))*(cos(60))));
    eq2 = (gauge2 - (e_x*((cos(120)).^2)) +(e_y*((sin(120)).^2)) + (lamda_xy*(sin(120))*(cos(120))));
    solve(eq0,eq1,eq2,e_x,e_y,lamda_xy);
    

Walter Roberson 2022-6-30

在 MATLAB Online 中打开

@Hiril Patel

ch0 = readmatrix('ch0.csv');

Those ch0, ch1, ch2 are probably not scalars.

Channel0 = n*ch0;

so the Channel* variables are probably not scalars.

gauge0 = (4/2.04)*(Channel0/E);

and that makes the gauge* variables not scalars.

    eq0 = (gauge0 - (e_x*((cos(0)).^2)) +(e_y*((sin(0)).^2)) + (lamda_xy*(sin(0))*(cos(0))));

So the eq* variables are individually probably not scalars, since they are in terms of the gauge variables that are (probably) not scalars.

solve(eq0,eq1,eq2,e_x,e_y,lamda_xy);

You are asking to solve those arrays of equations that are in terms of 3 scalar variables e_x ,e_y, lamda_xy and you are asking for a single e_x and e_y and lamda_xy that solves those arrays simultaneously.

For example if ch0 is 10 x 1 then eq0 would be 10 x 1, and your call to solve would be solve(10x1, 10x1, 10x1, scalar, scalar, scalar).

solve() is the simultaneous equation solver. When you pass it more than one equation, it has to find the values of the free variables that make all of the equations true at the same time.

What you can do is arrayfun():

  sols = arrayfun(@(E0,E1,E2)) solve(E0,E1,E2,e_x,e_y,lamda_xy), eq0, eq1, eq2, 'uniform', 0);
  

I used uniform, 0 because there might be no solutions in some cases, or there might be multiple solutions perhaps.

Hiril Patel 2022-9-18

Hello again,

I had to change the formula since this one didn't yielded true results. But right now I don't know how to ask this query on internet so I had to ask it here.

the new formula contains serveral condition in order to get correct resutls. I want to know how to apply those condtion on each cell. Here is the query:

I have three equal size csv file. I have to take one value from each file from same row of those three file and compute it to get a value. I was able to do that, it is simple. But now what I need its that those computed value needs to be passed from certain condtion in order to apply next formula in order to get true value. Can you tell me how should i take those computed value(all the computed values satishfy a certain condition on which their formula changes).

I hope I have explained it in understandable way.

for more information, I am using these base CSV value to get principle strain value and principle strain direction.( I am able to find principle strain value but the direction has some condition in order to get it calculated).

this is hte reference document:( on page 197 and 198)

https://d1wqtxts1xzle7.cloudfront.net/44775005/An_Introduction_to_Measurements_using_Strain_Gages-with-cover-page-v2.pdf?Expires=1663533520&Signature=M9JIjnPDt-s9E~EJgEmtKS9Upn5PQtALRdkohL9O7~L-LnVKwFcJ9Y56s-VZSs9K8JDP5jsjbTfuZxel03mLz550OnCJBDOQ5XKWtDaKMmOAKn7w6QyDaONjm~9gV3i3TxlN~SqVzO9npY4En0-CWwzdMbdkFAhrurOV7iROWhDbNKtIQa5JIrvBQC7pvEMFniuL3hybZTY3oEgb7HYSpbifde9x0IOEvJZgKpRsPUOdoSu-uQQ2DE6DNVlpXi4c3V7utGwaBqSSbieLhiEQTHcA-IJtYI3bmwhz120Us1wDqF8jXtFqdMPlM5o9~y2RF3tK9xlOhEMMUcdhfHOLAA__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA

thank you

Hiril Patel 2022-9-18