How to fix this issue, I'm trying to run a temperature sensor in Arduino Uno

>> % Create Arduino object

a = arduino();

% Define pin numbers

lm35Pin = 'A0';

fanPin = 'D9';

% Threshold temperature values (manipulate values if necessary)

fanOnTemp = 30.0;

fanOffTemp = 35.0;

% Create figure and axes

figure;

ax = axes('Parent', gcf);

% Initialize variables

time = 0;

temperature = 0;

fanState = 0; % 0 = Fan off, 1 = Fan on

% Initialize arrays to store temperature and time data

maxDataPoints = 60; % Adjust the number of data points to display

timeData = zeros(1, maxDataPoints);

temperatureData = zeros(1, maxDataPoints);

% Plot the initial data

plot (ax, timeData, temperatureData, 'r', 'LineWidth', 2);

xlabel ('time (s)');

ylabel ('Temperature (°C)');

title ('Real-Time LM35 Temperature Plot');

grid on;

xlim ([0, maxDataPoints]);

ylim ([min(temperatureData)-1, max(temperatureData)+1]); % Initialize y-axis limits

% Main loop

while true

% Read voltage from LM35D2 sensor

sensorValue = readVoltage (a, lm35Pin);

% Convert sensor value to temperature in Celsius

voltage = sensorValue * (1 / 0.00488750);

temperature = voltage * 0.48828125;

% Print the temperature

fprintf ('Temperature: %.2f*C\n', temperature);

% Store the temperature and time data in arrays

timeData = [timeData (2:end), time];

temperatureData = [temperatureData(2:end), temperature];

% Update the plot

set (ax, Children, 'XData', timeData, 'YData', temperatureData);

% Adjust y-axis limits to fit the current temperature range

ylim ([min(temperatureData)-1, max(temperatureData)+1]);

% Check if temperature exceeds the threshold to turn on the fan

if temperature > fanOnTemp && ~fanState

% Turn on the fan

writeDigitalPin(a, fanPin, 1);

disp('Fan is ON');

fanState = 1;

elseif temperature < fanOffTemp && fanState

% Turn off the fan

writeDigitalPin(a, fanPin, 0);

disp('Fan is OFF');

fanState = 0;

end

% Delay between readings

pause(1);

% Update time

time = time + 1;

end

Error: The end operator must be used within an array index expression.

I highlighted the error in bold style.

Answer 1

[Manikanta Aditya]

Hi @Seer John Lucas

The error message you’re seeing is due to the use of end in the set function call. In MATLAB, end is used to refer to the last element of an array or matrix. However, it can only be used within an array index expression.

This code will fix the errors you encountered:

% Create Arduino object
a = arduino();
% Define pin numbers
lm35Pin = 'A0';
fanPin = 'D9';
% Threshold temperature values (manipulate values if necessary)
fanOnTemp = 30.0;
fanOffTemp = 35.0;
% Create figure and axes
figure;
ax = axes('Parent', gcf);
% Initialize variables
time = 0;
temperature = 0;
fanState = 0; % 0 = Fan off, 1 = Fan on
% Initialize arrays to store temperature and time data
maxDataPoints = 60; % Adjust the number of data points to display
timeData = zeros(1, maxDataPoints);
temperatureData = zeros(1, maxDataPoints);
% Plot the initial data
h = plot(ax, timeData, temperatureData, 'r', 'LineWidth', 2);
xlabel ('time (s)');
ylabel ('Temperature (°C)');
title ('Real-Time LM35 Temperature Plot');
grid on;
xlim ([0, maxDataPoints]);
ylim ([min(temperatureData)-1, max(temperatureData)+1]); % Initialize y-axis limits
% Main loop
while true
    % Read voltage from LM35D2 sensor
    sensorValue = readVoltage (a, lm35Pin);
    % Convert sensor value to temperature in Celsius
    voltage = sensorValue * (1 / 0.00488750);
    temperature = voltage * 0.48828125;
    % Print the temperature
    fprintf ('Temperature: %.2f*C\n', temperature);
    % Store the temperature and time data in arrays
    timeData = [timeData(2:end), time];
    temperatureData = [temperatureData(2:end), temperature];
    % Update the plot
    set(h, 'XData', timeData, 'YData', temperatureData);
    % Adjust y-axis limits to fit the current temperature range
    ylim ([min(temperatureData)-1, max(temperatureData)+1]);
    % Check if temperature exceeds the threshold to turn on the fan
    if temperature > fanOnTemp && ~fanState
        % Turn on the fan
        writeDigitalPin(a, fanPin, 1);
        disp('Fan is ON');
        fanState = 1;
    elseif temperature < fanOffTemp && fanState
        % Turn off the fan
        writeDigitalPin(a, fanPin, 0);
        disp('Fan is OFF');
        fanState = 0;
    end
    % Delay between readings
    pause(1);
    % Update time
    time = time + 1;
end

Hope it helps.