Matlab cannot read data from MAX6675 through Arduino
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I tested a MAX6675 module using "max6675.h" library on Arduino IDE to measure temperature with type K thermocouple. It worked well.
Then I connected Arduino UNO with Arduino Support Package in Matlab to read data from the MAX6675 module.
a=arduino('com4','uno','Libraries','SPI');
And I set SPI object:
max6675=spidev(a,'D10')
This was what command window showed:
I tested the reading with these commands:
din=zeros(1,2);
dato=writeRead(max6675,din,'uint16')
And the result was:
It is not possible those values. Temperature in the room is tipically 19°C. The result must be [0 76] or something like that. I used a digital multimeter to test "CS" and "D10" pins and voltage remained in high state while "writeRead" function was executed. It should change from high to low level according to SPI protocol during reading operation on MAX6675.
What am I doing wrong?
回答（3 个）
Uwe Weltin
2023-1-23
2 个投票
% KTYPE.m This example is based on the reference manual of the MAX6675 amplifier
% LED Versuch
clear all, close all
ComPort=getAvailableComPort
a = arduino(ComPort{1},'Uno','Libraries','SPI')
tmax= 30;
fs = 8;
dt = 1/fs;
t = [dt:dt:tmax];
il = length(t);
T = zeros(il);
dummy = [uint8(0),uint8(0)];
for i=1:il
datOut = writeRead(MAX6675,dummy); % Read MAX6675
pause(0.5)
BINR = [dec2bin(datOut(1),8), dec2bin(datOut(2),8)]; % Show the bits of the read
DECR = bin2dec(BINR);
DECT = bitshift(DECR,-3); % Shift by 3 bits to the right
BINT = dec2bin(DECT); % Just to show the change
MP = 255/1023.75; % Reading 0 means 0°C,
% Reading 255 its hot as 1023.75°C
T(i) = MP*DECT; % Factor to get °C
disp(T(i))
end
Daniel Melendrez
2019-12-4
编辑：Daniel Melendrez
2019-12-4
0 个投票
Oscar
I am working at the moment on a big project that uses the MAX6675. Here are some pieces of advice based on my experience:
- I would delegate the full data conversion to the Arduino itself. Do not use Matlab to convert the data. Meaning that I would only use Matlab for reading the converted value and displaying it in the console or in a plot.
- Don't forget that each conversion time is about 250 ms (read the datasheet, page 2), therefore, you need to query Arduino if the conversion is ready after this time. In my application I implemented a serial query routine that "spits out" the temperature value once it's ready.
Hope this helps for now
Daniel
2 个评论
Yo
2021-3-31
Daniel,
I see this is an old question. Is it possible to read the thermocouple temperature from simulink?
Marco
Atta Wasay
2023-11-8
Here is the simulink model.
gdz
2022-12-13
0 个投票
I have done something the similar, dato give [4 4], the second run dato give [63491,63491], and the following run repeated with [4,4], [63491,63491], and [2052,2052]. Does anyone know what's happenning here?
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2019-9-18
2023-11-8
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