Help converting CAN Payload in String format to engineering unit

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Harpreet Singh 2024-7-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2134861-help-converting-can-payload-in-string-format-to-engineering-unit

评论： Harpreet Singh 2024-7-16

采纳的回答： Arjun

Hello,

I have the following valiable in Matlab which holds the CAN data from a recorder in the following format:

Hexadecimal

The output of Row 1047 Should be -1951 normally and -1.951 after factoring it by 0.001. This conversion is done using this website.This is basically a force value of a Dynamometer. How can I do this conversion in Matlab? Any known function?

The closest example I found is here, but does not actually solves my problem.

The DBC is as follows:

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Stephen23 2024-7-16

在 MATLAB Online 中打开

T = "61,F8,FF,FF";
N = double(typecast(uint8(sscanf(T,'%x,')),'int32'))*0.001
N = -1.9510

Harpreet Singh 2024-7-16

Thank you, pretty effecient code this.

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Answer 1

Arjun 2024-7-15

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https://ww2.mathworks.cn/matlabcentral/answers/2134861-help-converting-can-payload-in-string-format-to-engineering-unit#answer_1485258

在 MATLAB Online 中打开

As per my understanding you have a table of values and you are specifically interested in converting the payload from a comma separated hexadecimal string to a number in engineering unit and then scale it using the scaling factor of 0.001. One way to do so is as follows:

First parse the payload string and remove the comma using the split function to convert into 4x1 string array.
Convert the string so obtained to decimal from hexadecimal using hex2dec function.
Convert the data to bytes using the uint8 function.
Use the typecast function to convert the bytes data to signed 32-bit Integer.
Finally apply the scaling factor to get the desired result.

You can refer to the following code that corresponds to the above approach:

%String to be converted
payload_str = "61,F8,FF,FF";
%Conversion to bytes after removing comma and converting to decimal
payload_bytes = uint8(hex2dec(split(payload_str, ',')));
%Interpret as a 32-bit signed integer
raw_value = typecast(payload_bytes, 'int32');
scaling_factor = 0.001;
%apply the scaling factor
engineering_value = double(raw_value) * scaling_factor;
disp(engineering_value);

The code produced an output of –1.951 for the given inputs.

Please refer to the following documentation links for more information on the split, uint8, hex2dec and typecast functions respectively:

I hope this helps!

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Harpreet Singh 2024-7-15

Hello Arjun, thank you for your response. I also resolved this the same way, but I have two approaches as sometime you will have signals spread "partially" across 2 bytes as seen below.

For CAN signals spread partially the code section below will work well.

%% Exaple for partial signals

payload_str = "DF,5A,3F,19,00,B0,1F,05";

%Splitting payload_str

payload_split = split(payload_str,',');

%Reversing (Intel/Little Endian) and appending relevant bytes

payload_required = append(payload_split(7), payload_split(6));

%hexstring to binary

payload_binary = hexToBinaryVector(payload_required);

%Trimming to data bits per the photo above

payload_binary_trimmed = payload_binary(:,1:end-3);

%Trimmed binary to decimal

decimal = binaryVectorToDecimal(payload_binary_trimmed);

%Decimal to engineering values through scaling and offset

scale = 0.08;

offset= -40;

Eng_Value = (decimal*scale)+offset;

All the hard coded values to index the "payload_required" and trim "payload_binary_trimmed" can managed by refering to DBC directly using the "canDatabase" function.

Your method is approcal one when the signal counumes complete bytes.

Thank you once again.

Arjun 2024-7-16